掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

A Rayleigh-type surface acoustic wave (SAW) is used in various fields as classical and quantum information carriers because of its surface localization, high electrical controllability, and low propagation loss. Coupling and hybridization between the SAW and other physical systems such as magnetization, electron charge, and electron spin are the recent focuses in phononics and spintronics. A precise measurement of the surface wave amplitude is often necessary to discuss the coupling strengths. However, there are only a few such measurement techniques and they generally require a rather complex analysis. Here we develop and demonstrate a straightforward measurement technique that can quantitatively characterize the SAW. The technique optically detects the surface waving due to the coherently driven SAW by the optical path modulation. Furthermore, when the measurement system operates in the shot-noise-limited regime, the surface slope and displacement at the optical spot can be deduced from the optical path modulation signal. Our demonstrated technique will be an important tool for SAW-related research.

DOI： 10.1103/PHYSREVB.107.165416

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

The ability to drive a spin system to state far from the equilibrium is indispensable for investigating spin structures of antiferromagnets and their functional nonlinearities for spintronics. While optical methods have been considered for spin excitation, terahertz (THz) pulses appear to be a more convenient means of direct spin excitation without requiring coupling between spins and orbitals or phonons. However, room-temperature responses are usually limited to small deviations from the equilibrium state because of the relatively weak THz magnetic fields in common approaches. Here, we studied the magnetization dynamics in a HoFeO3 crystal at room temperature. A custom-made spiral-shaped microstructure was used to locally generate a strong multicycle THz magnetic near field perpendicular to the crystal surface; the maximum magnetic field amplitude of about 2 T was achieved. The observed time-resolved change in the Faraday ellipticity clearly showed second- and third-order harmonics of the magnetization oscillation and an asymmetric oscillation behaviour. Not only the ferromagnetic vector M but also the antiferromagnetic vector L plays an important role in the nonlinear dynamics of spin systems far from equilibrium.

DOI： 10.1038/s41467-023-37473-1

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その他リンク： https://www.nature.com/articles/s41467-023-37473-1

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Spin-orbit torque (SOT) switching in chiral antiferromagnets, such as D019-Mn3Sn, has opened prospects in antiferromagnetic spintronics. In this paper, we investigated the critical switching voltage as a function of the voltage pulse width in order to explore the thermal stability factor Δ in the D019-Mn3Sn. Although the critical switching voltage is found to decrease with increasing the voltage pulse width as expected by the thermally activated switching process with Δ of 131.1 at 300 K, our detailed examinations reveal that the Joule heating due to the voltage pulse could induce the magnetic phase transition in the D019-Mn3Sn, which significantly alters the energy landscape relevant to the SOT switching. This assisting mechanism for the SOT switching inhibits an accurate determination of Δ but could deliver a smaller Δ than the actual. Our study provides cautionary note in estimating the thermal stability of the chiral antiferromagnets.

DOI： 10.1063/5.0144602

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Applied  

Terahertz (THz) magnetization dynamics is a key property of antiferromagnets and ferrimagnets that could harness the THz forefront and spintronics. While most of the present THz measurement techniques are for bulk materials, the sensitivities of which rely on the volume of material, measurement techniques suitable for thin films are quite limited. In this study, we explore and demonstrate the electrical detection of the antiferromagnetic dynamics in ferrimagnetic Gd-Co thin films by using a 154-GHz gyrotron, which is a high-power electromagnetic wave source. Captured resonant modes allow us to characterize the peculiar magnetization dynamics of Gd-Co around the net angular momentum compensation. As the gyrotron frequency is scalable up to THz, our demonstration is a milestone toward THz measurements for antiferro- and ferrimagnetic thin films.

DOI： 10.1103/physrevapplied.19.l031003

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevApplied.19.L031003/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本磁気学会  

The superconducting diode effect in which electrical resistance is zero in only one direction has recently been reported in superconductors without inversion symmetry. Previous studies investigated the nonreciprocity of the critical current, but little has been known about the rectification effect when AC currents are applied. Herein, we examined the rectification characteristics of a non-centrosymmetric Nb/V/Ta artificial superlattice under AC currents. The rectification strength can be modulated by an applied magnetic field, and its polarity can be tuned by the magnetic field. Furthermore, we find that the magnetic field dependence of the rectification is different from that of the nonreciprocal critical current.

DOI： 10.3379/msjmag.2309r001

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CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Recently, an ultimate diode effect, a superconducting diode where an electric current shows the superconducting state in one direction and the normal state in the other direction, has been discovered in a noncentrosymmetric Nb/V/Ta superlattice. Here, we report that the polarity of the superconducting diode shows a sign reversal as a magnetic field is increased. Such a nonlinear behavior of the diode effect is beyond the phenomenology based on the Ginzburg-Landau theory. Based on a recent microscopic study, we propose the crossover and phase transitions of the finite-momentum pairing states as a possible origin of the sign reversals.

DOI： 10.35848/1882-0786/AC99B9

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

We demonstrate that magnetic crystal anisotropy ( Ku ) and spectroscopic g-factor can be modulated simultaneously by gate voltage in a Pt/Co/MgO ultrathin film with our ferromagnetic resonance (FMR) measurement based on the rectification effect. The g-factor reflects on orbital magnetic moment, indicating that the electric field induced-modulations of magnetic anisotropy in cobalt originate from the change of the anisotropy of orbital moments ( ΔmL ). The quantitative estimation reveals that ΔmL to Ku correlation when the electric field is applied significantly differs from the one inherent at the Pt/Co/MgO interfaces. This means that the correlation itself is also modulated by the electric field. Our results show that the FMR technique is very useful for probing the electric field effect on Ku.

DOI： 10.35848/1347-4065/AC9025

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The magnetic damping constant is a proportionality constant for energy dissipation upon the precession of the magnetic moment, and it characterizes magnetization dynamics. In this study, ferrimagnetic Gd3Fe5O12 (111) epitaxial films are grown using pulsed laser deposition, and the temperature dependence of the ferrimagnetic resonance and damping constant (αFiM) is investigated. The results reveal that αFiM is approximately an order of magnitude smaller than those of other ferrimagnetic metals reported to date. Our results emphasize the potential of Gd3Fe5O12 films in ultralow-power spintronic applications.

DOI： 10.1063/5.0099618

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Chiral antiferromagnets are regarded as a new class of antiferromagnets owing to its intriguing spin transport properties such as a sizable anomalous Hall effect (AHE). In this work, we fabricated chiral antiferromagnetic L12-Mn3Ir (111)-oriented films and investigated the anomalous Hall conductivity with respect to the chemical order parameter S. It is found that the anomalous Hall conductivity in (111)-oriented films is much more pronounced compared to (001)-oriented films, which is consistent with the theoretical prediction. We also found that the anomalous Hall conductivity strongly depends on the longitudinal conductivity, which could suggest an extrinsic contribution to the AHE in L12-Mn3Ir.

DOI： 10.35848/1347-4065/ac7625

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その他リンク： https://iopscience.iop.org/article/10.35848/1347-4065/ac7625/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Nanotechnology  

The diode effect is fundamental to electronic devices and is widely used in rectifiers and a.c.–d.c. converters. At low temperatures, however, conventional semiconductor diodes possess a high resistivity, which yields energy loss and heating during operation. The superconducting diode effect (SDE)1–8, which relies on broken inversion symmetry in a superconductor, may mitigate this obstacle: in one direction, a zero-resistance supercurrent can flow through the diode, but for the opposite direction of current flow, the device enters the normal state with ohmic resistance. The application of a magnetic field can induce SDE in Nb/V/Ta superlattices with a polar structure1,2, in superconducting devices with asymmetric patterning of pinning centres9 or in superconductor/ferromagnet hybrid devices with induced vortices10,11. The need for an external magnetic field limits their practical application. Recently, a field-free SDE was observed in a NbSe2/Nb3Br8/NbSe2 junction; it originates from asymmetric Josephson tunnelling that is induced by the Nb3Br8 barrier and the associated NbSe2/Nb3Br8 interfaces12. Here, we present another implementation of zero-field SDE using noncentrosymmetric [Nb/V/Co/V/Ta]20 multilayers. The magnetic layers provide the necessary symmetry breaking, and we can tune the SDE by adjusting the structural parameters, such as the constituent elements, film thickness, stacking order and number of repetitions. We control the polarity of the SDE through the magnetization direction of the ferromagnetic layers. Artificially stacked structures13–18, such as the one used in this work, are of particular interest as they are compatible with microfabrication techniques and can be integrated with devices such as Josephson junctions19–22. Energy-loss-free SDEs as presented in this work may therefore enable novel non-volatile memories and logic circuits with ultralow power consumption.

DOI： 10.1038/s41565-022-01159-4

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その他リンク： https://www.nature.com/articles/s41565-022-01159-4

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We grew epitaxial thin films of hematite (α-Fe2O3) on (0 0 0 1) Al2O3 substrates by pulsed laser deposition and investigated their magnetic properties. α-Fe2O3 films grown at lower temperatures are found to undergo the Morin transition at higher temperatures, implying that lowering the growth temperature and managing lattice defects associated with strain relaxation are key to realizing Morin transition. We also characterized films' magnetic properties by spin Hall magnetoresistance (SMR). We show that tri-axial magnetic anisotropy can be detected as SMR features having a 60° period with respect to in-plane magnetic field rotations. Furthermore, a large change in SMR ratio associated with Néel vector re-orientation due to Morin transition is seen. Details of SMR properties for α-Fe2O3 films and their analysis results, including the influence of the fabrication process on SMR behaviors, are discussed.

DOI： 10.1063/5.0087643

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The development of spintronics applications using the spin-orbit torque from the spin Hall effect is expected to advance the low-power consumption of various information devices. However, the dependence of the spin Hall effect on the crystal symmetry of the material has not been studied in detail. In this work, we investigate the dependence of the spin Hall angle on crystal orientation for epitaxial Pt in Pt/FeNi systems by using multiple ferromagnetic resonance techniques. Our estimation of the spin Hall angle indicates that the efficiency of spin current generation via the spin Hall effect can vary depending on the direction in which the spin current flows out, while the direction of the charge current has less impact on this efficiency.

DOI： 10.1063/5.0078688

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Magnetism and Magnetic Materials  

In this work, we examine the temperature dependence of magnetic domain wall (DW) creep motion in ferrimagnetic Tb/CoFeB/MgO microwires by using a real-time DW detection method. By measuring the field-dependent DW velocity at various temperatures, the creep-scaling constant and the characteristic velocity were evaluated from the creep-scaling analysis. We found that the DW velocity changed significantly with temperature and was mainly attributed to the variation in the creep-scaling constant than that in the characteristic velocity. Possible mechanisms for the temperature dependence of each parameter are discussed.

DOI： 10.1016/j.jmmm.2022.169251

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Applied  

Unlike ferromagnets, collinear antiferromagnets have two precession modes exhibiting opposite chirality, which enables the use of the polarization degree of freedom of magnons. In this study, we experimentally measure the polarization-selective spectra of magnetic resonance in perpendicularly magnetized synthetic antiferromagnets using a wideband crossed microstrip circuit. The magnetic resonances with right-handed and left-handed precession modes are directly detected, and theoretical analysis and numerical simulations explain the measurement results by considering the difference in the perpendicular magnetic anisotropy and damping constant between the top and bottom ferromagnetic layers. We also show that magnetic excitations with different polarization types can be excited under degeneracy between the two precession modes. Our work suggests that perpendicularly magnetized synthetic antiferromagnet structures provide an attractive platform for manipulating the polarization degree of freedom of magnons.

DOI： 10.1103/PHYSREVAPPLIED.18.014032

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Magnetism and Magnetic Materials  

We investigated the Bi composition, film thickness, and annealing temperature (Ta) dependence of the magnitude of the longitudinal spin Seebeck effect (LSSE) voltage in BixY3-x Fe5O12 (0 ≤ x ≤ 1.2) (Bi-YIG) films on a Si substrate, prepared using sol–gel solution and spin-coating methods. The Bi-YIG garnet films exhibited a polycrystalline structure, and the thickness of the film formed by the agglomeration of nanoparticles was approximately 50 nm. The LSSE coefficient (S) of the Bi-YIG/Pt (5 nm) films tends to increase with increasing Bi composition (0 ≤ x ≤ 0.8), and the value of the S at x = 0.8 is 1.7 times larger than that at x = 0. When the Bi composition is 0 ≤ x ≤ 0.8, the values of the saturation magnetization and resistivity are almost constant regardless of x, and the value of the Gilbert damping constant increases with increasing x, while the values of the spin mixing conductance and maximum Kerr rotation angle are tended to increase with increasing x. This result indicates that the increasing tendency of the S occurs because of the induced of effective spin current conversion in the Pt layer thorough Bi-YIG due to the enhancement of interface effect between the Pt and Bi-YIG by Bi substitution. In addition, a large S is obtained in Bi-YIG films annealed at Ta = 973 K because the films contained few cracks and smooth surface conditions.

DOI： 10.1016/j.jmmm.2022.169416

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Spin current transmission in antiferromagnets is one of the most interesting focuses in antiferromagnetic spintronics. Its study may provide access to spin superfluid physics, which gives rise to metastable spin supercurrents. In this work, we investigate the spin current transmission in a single-crystalline NiO (111) and NiO (001) of the NiO/Fe20Ni80 and Pt/NiO/Fe20Ni80 epitaxial films by the spin-pumping enhanced damping of FeNi. The spin transmission length is estimated to be λNiO(111) = 50 ± 4 nm and λNiO(001) >> 100 nm for NiO (111) and NiO (001), respectively. The results are succinctly discussed in the framework of the spin superfluidity mechanism.

DOI： 10.35848/1882-0786/ac3575

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Magnetic properties of the Pt/Py microstrip were investigated using the simultaneous electrical and optical detection of spin-torque ferromagnetic resonance. From the measured optical signal using the heterodyne-magneto-optical Kerr effect (MOKE), we found that the inhomogeneous broadening and Gilbert damping constant were modified along the transverse direction of the microstrip. In addition, a difference in the precession phase was also observed owing to the non-uniform out-of-plane microwave field. Our study shows that the ferromagnetic resonance measurement based on the heterodyne-MOKE technique is a powerful tool for characterizing the static and dynamic magnetic properties of magnetic thin films with sub-micrometer spatial resolution.

DOI： 10.1063/5.0070012

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Magnetism and Magnetic Materials  

The changes of longitudinal spin Seebeck (LSSE) voltage with annealing temperature Ta and time in Y3Fe5O12 (YIG) films formed by densely packed nanocrystals on a Si substrate have been investigate. The value of thermoelectric performance (TP) decreases monotonically with increasing Ta from 1073 K to 1273 K, and it decreases by up to 24% (64%) in the YIG films with Pt = 5 nm (10 nm). The decreased TP is also observed with increasing annealing time. These results indicate that the microstructural changes in the YIG films by annealing temperature and time are caused the decreased TP, which are corresponded with a reduced coherence of the magnons in the YIG films.

DOI： 10.1016/j.jmmm.2021.168093

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The interlayer exchange coupling (Jex) in a perpendicularly magnetized synthetic antiferromagnet (p-SAF) is an important factor in the properties of domain wall (DW) motion driven by spin-orbit torque (SOT). In this study, we investigate experimentally and numerically how Jex affects the critical current density (Jc) of DW motion in an SOT-driven p-SAF. We also study how Jex affects the DW deflection angle (θDW), which is defined as the relative angle between the initial magnetization direction in the DW and the final one upon the injection of spin current. Positive correlation is found between Jex and Jc, which can be attributed to the suppression of θDW. Our results reveal how Jex affects the driving current of DW motion in an SOT-driven p-SAF.

DOI： 10.1063/5.0056056

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Antiferromagnets are one of the few candidate materials that can work at THz frequency and are, therefore, a potential material for THz technology recently attracting interest from high-speed communication and sensing applications. In this work, we investigate an antiferromagnetic resonant frequency (ωr) tunability for cation doped α-Fe2O3. It is found that, with various cation dopants (Al, Ru, Rh, and In), the resonant frequency can be tuned in a range between a millimeter-wave band and a THz band. We also complementally discuss the mechanism of the Morin temperature (TM) shift upon cation doping by the temperature and dopant dependence of ωr. A good frequency tunability shown in this work suggests that cation doped α-Fe2O3 is a useful material for millimeter-wave and THz applications.

DOI： 10.1063/5.0053586

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We report that the superconducting critical magnetic field can be nonreciprocal under a bias of an electric current in a superconducting [Nb/V/Ta] n superlattice without a center of inversion. The critical magnetic field showed a clear difference between positive and negative magnetic fields. Furthermore, the magnitude relation between the positive and negative critical magnetic fields is reversed when the direction of the electric current is reversed. Our findings indicate that the superconducting gap can be anisotropic by the application of an electric current.

DOI： 10.35848/1882-0786/ac03c0

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Magnetics Society of Japan  

Chiral antiferromagnets have recently been drawing attention due to their unique magnetic transport properties such as the giant anomalous Hall effect. We previously reported an experimental demonstration of the giant anomalous Hall effect in the chiral antiferromagnet Mn3Ir thin films with quite blunt hysteresis curves suggesting a large distribution of magnetic properties associated with magnetic domains. In this work, we measured the anomalous Hall effect and its hysteresis curve in the Mn3Ir of various device sizes. By comparing the experimental data with our developed statistical model, we characterize a distribution of the magnetic domain size in our Mn3Ir films.

DOI： 10.3379/msjmag.2107l002

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Artificially engineered superlattice offers highly flexible control of the quantized electronic state by manipulating its lattice structure. We fabricated artificially engineered superlattices [Nb/V/Ta]n as a new class of superconducting superlattices and investigated the upper critical field Hc2 in terms of the structural difference. It is found that the out-of-plane upper critical field Hc2⊥ significantly increases compared with that of a Nb single layer film as the thickness of the constituent Nb, V, and Ta layers becomes thin. In the case of the superlattice [Nb/V/Ta]n, the Hc2⊥ is basically governed by the orbital pair-breaking effect rather than Pauli pair-breaking effect and increases only when the crystalline size of the superlattice decreases by the insertion of V layers. Thus, we conclude that the shortening of the coherence length of Cooper pairs due to the crystalline disorder predominantly contributes to the increase of the Hc2⊥ in the superlattice [Nb/V/Ta]n.

DOI： 10.35848/1347-4065/abfdc1

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その他リンク： https://iopscience.iop.org/article/10.35848/1347-4065/abfdc1/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics Condensed Matter  

Magnonics is a budding research field in nanomagnetism and nanoscience that addresses the use of spin waves (magnons) to transmit, store, and process information. The rapid advancements of this field during last one decade in terms of upsurge in research papers, review articles, citations, proposals of devices as well as introduction of new sub-topics prompted us to present the first roadmap on magnonics. This is a collection of 22 sections written by leading experts in this field who review and discuss the current status besides presenting their vision of future perspectives. Today, the principal challenges in applied magnonics are the excitation of sub-100 nm wavelength magnons, their manipulation on the nanoscale and the creation of sub-micrometre devices using low-Gilbert damping magnetic materials and its interconnections to standard electronics. To this end, magnonics offers lower energy consumption, easier integrability and compatibility with CMOS structure, reprogrammability, shorter wavelength, smaller device features, anisotropic properties, negative group velocity, non-reciprocity and efficient tunability by various external stimuli to name a few. Hence, despite being a young research field, magnonics has come a long way since its early inception. This roadmap asserts a milestone for future emerging research directions in magnonics, and hopefully, it will inspire a series of exciting new articles on the same topic in the coming years.

DOI： 10.1088/1361-648x/abec1a

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/abec1a/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Magnetics Society of Japan  

We report antiferromagnetic spin wave resonance in perpendicularly magnetized synthetic antiferromagnets consisting of Co/Ni multilayers and a thin Ru spacer layer. Two resonance modes were observed in the finite range of the out-of-plane bias magnetic field, where two magnetic moments separated by the Ru layer were antiferromagnetically aligned. These two modes show an opposite dependence on the bias magnetic field and correspond to right- and left-handed polarized spin waves. We also theoretically derive the spin wave dispersion for the perpendicularly magnetized synthetic antiferromagnets on the basis of an equation of motion. Our experimental results show good agreement with the theoretical analysis.

DOI： 10.3379/msjmag.2103r004

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

To enhance thermal stability while keeping low driven current is difficult in traditional domain wall (DW) motion devices. The increasing of energy barrier for thermal stability inevitably results in the enhancement of driven current. We numerically investigate depinning field (Hdepin) and critical current density (Jc) for DW motion as a function of uniaxial magnetic anisotropy (Ku) in vertical DW motion memory with artificial ferromagnet. It is found that Hdepin and Jc show different Ku dependence. The results indicate that it is promising to simultaneously achieve high thermal stability and low driven current in artificial ferromagnet based DW motion devices.

DOI： 10.35848/1882-0786/abd86a

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その他リンク： https://iopscience.iop.org/article/10.35848/1882-0786/abd86a/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

We studied field-driven domain wall (DW) creep motion in ferrimagnetic Tb/CoFeB/MgO with respect to CoFeB thickness by using a real-time DW detection method. The DW velocity for Tb(5 nm)/CoFeB(1.0 ∼ 1.8 nm)/MgO microwires was measured at room temperature. The DW velocity increases with increasing the CoFeB thickness, which is contrary to a general trend in the ferromagnetic wire. From the creep-scaling analysis, the characteristic velocity at which the DW moves when the energy barrier vanishes is found to be a dominant contribution to the DW velocity. Our results clarify the ferrimagnetic DW dynamics in the creep regime.

DOI： 10.35848/1347-4065/abd67d

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その他リンク： https://iopscience.iop.org/article/10.35848/1347-4065/abd67d/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Magnetics Society of Japan  

We propose a new structure of vertical domain wall (DW) motion memory with artificial ferromagnet to achieve high DW controllability. The artificial ferromagnet is composed of periodically stacked ferromagnetic bilayers with relatively large and small exchange stiffness constants (Aex), which refer to as strong coupling layers and weak coupling layers. By optimizing Aex and the magnetic anisotropy of the weak coupling layers, DW width and position can be easily controlled. Furthermore, micromagnetic analysis shows that low critical current density for DW motion down to 2 ×1010 A/m2 can be achieved as we increase the Aex of weak coupling layers to larger than 2 pJ/m.

DOI： 10.3379/msjmag.2011r002

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Magnetics Society of Japan  

The angular momentum compensation temperature, TA, in transition metal rare earth (TM-RE) ferrimagnetic materials is a crucial property for utilizing antiferromagnetic spin dynamics, which is much faster than its ferromagnetic counterpart. However, reports on the estimation of TA in ferrimagnets are limited. In this study, we measured the temperature dependence of the spin magnetization and orbital magnetization of GdFe amorphous perpendicular magnetization film by using magnetic Compton scattering. Then, we estimated TA experimentally.

DOI： 10.3379/msjmag.2101l002

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1097/ALN.0000000000004016

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

The propagation of coherent spin waves in permalloy microstrips was investigated using a heterodyne-magneto-optical Kerr effect technique. The two-dimensional imaging reveals the mode interference with a high-order spin-wave mode along the microstrip width. The spin-wave dispersion relations across the microstrip width were deduced from fast Fourier transformations on the complex spin-wave amplitude of the one-dimensional scan, and multiple spin-wave modes were observed at the edges of the microstrips. These experimental results provide direct evidence for the quantization of spin-wave dispersion due to the finite width of the microstrips and enables us to evaluate the attenuation length for each quantized spin-wave mode.

DOI： 10.1103/PhysRevB.102.214440

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The antiferromagnetic order can mediate a transmission of the spin angular momentum flow, or the spin current, in the form of propagating magnons. In this work, we perform laser stimulated THz emission measurements on Pt/CoO/FeCoB multilayers to investigate the spin current transmission through CoO, an antiferromagnetic insulator, on a picosecond timescale. The results reveal a spin current transmission through CoO with the diffusion length of 3.0 nm. In addition, rotation of the polarization of the emitted THz radiation was observed, suggesting an interaction between the propagating THz magnons and the Néel vector in CoO. Our results not only demonstrate the picosecond magnon spin current transmission but also the picosecond interaction of the THz magnons with the Néel vector in the antiferromagnet.

DOI： 10.1063/5.0020020

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Magnetics Society of Japan  

We numerically investigated the refraction property of spin waves (SWs) at thickness step in films with out-of-plane magnetization, in which the SWs propagate isotropically in the film plane. It was confirmed the isotropic SWs were refracted at a thickness step by following the Snell's law. We also found that the refraction angle of SWs of the dipole-exchange mode depends on the resonant frequency, indicating that the chromatic aberration effect should be taken into account in designing magnonic devices.

DOI： 10.3379/msjmag.2011l003

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Magnetism and Magnetic Materials  

This paper reports on dependence of the Gilbert damping constant α on the microstructure in nanocrystalline Y3Fe5O12 (YIG) coatings fabricated on a Si substrate by a sequence of co-precipitation, spin-coating, and annealing processes. When the annealing temperature Ta increases from 1023 K to 1323 K, the average particle size of the YIG crystals estimated by scanning electron microscopy increases from 64 nm to 217 nm, and the value of α also increases from 2.7 × 10−2 to 1.2 × 10−1. The observed increase of α is attributed to the microstructural evolution in the nanocrystalline YIG coatings upon annealing.

DOI： 10.1016/j.jmmm.2020.167253

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature  

Nonlinear optical and electrical effects associated with a lack of spatial inversion symmetry allow direction-selective propagation and transport of quantum particles, such as photons1 and electrons2–9. The most common example of such nonreciprocal phenomena is a semiconductor diode with a p–n junction, with a low resistance in one direction and a high resistance in the other. Although the diode effect forms the basis of numerous electronic components, such as rectifiers, alternating–direct-current converters and photodetectors, it introduces an inevitable energy loss due to the finite resistance. Therefore, a worthwhile goal is to realize a superconducting diode that has zero resistance in only one direction. Here we demonstrate a magnetically controllable superconducting diode in an artificial superlattice [Nb/V/Ta]n without a centre of inversion. The nonreciprocal resistance versus current curve at the superconducting-to-normal transition was clearly observed by a direct-current measurement, and the difference of the critical current is considered to be related to the magnetochiral anisotropy caused by breaking of the spatial-inversion and time-reversal symmetries10–13. Owing to the nonreciprocal critical current, the [Nb/V/Ta]n superlattice exhibits zero resistance in only one direction. This superconducting diode effect enables phase-coherent and direction-selective charge transport, paving the way for the construction of non-dissipative electronic circuits.

DOI： 10.1038/s41586-020-2590-4

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その他リンク： http://www.nature.com/articles/s41586-020-2590-4

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Spin-orbit torques (SOTs) acting in a Py/Pt/Co tri-layer, where the Py and Co layers are in-plane and perpendicularly magnetized, respectively, are investigated via the ferromagnetic resonance method. The resonance linewidth of the Py layer is clearly modulated by the DC bias current due to the damping-like SOT originated from the spin Hall effect in the Pt. In addition to this, the linewidth modulation efficiency is found to depend on the magnetization polarity of the perpendicularly magnetized Co layer. We conclude that this behavior comes from an additional damping-like SOT originating from the spin-orbit precession effect at the Pt/Co interface.

DOI： 10.35848/1882-0786/aba0dc

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その他リンク： https://iopscience.iop.org/article/10.35848/1882-0786/aba0dc/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

This paper introduces the concept of spin-orbit-torque-magnetic random access memory (SOT-MRAM) based physical unclonable function (PUF). The secret of the PUF is stored into a random state of a matrix of perpendicular SOT-MRAMs. Here, we show experimentally and with micromagnetic simulations that this random state is driven by the intrinsic nonlinear dynamics of the free layer of the memory excited by the SOT. In detail, a large enough current drives the magnetization along an in-plane direction. Once the current is removed, the in-plane magnetic state becomes unstable evolving toward one of the two perpendicular stable configurations randomly. In addition, we propose a hybrid CMOS/spintronics model to simulate a PUF realized by an array of 16 × 16 SOT-MRAM cells and evaluate the electrical characteristics. Hardware authentication based on this PUF scheme has several characteristics, such as CMOS-compatibility, non-volatility (no power consumption in standby mode), reconfigurability (the secret can be reprogrammed), and scalability, which can move a step forward the design of spintronic devices for application in security.

DOI： 10.1063/5.0013408

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Materials  

Antiferromagnets generally have a quite high magnetic resonance, as known as the antiferromagnetic resonance, whose frequency goes up to the THz range. They are one of the few materials that can magnetically couple to THz electromagnetic waves and are therefore important materials for THz technologies. In this work, we demonstrate that the THz resonance properties, such as resonant frequency and the Q factor, of antiferromagnetic NiO can be controlled over a wide range by substituting the Ni2+ cation with various different cations. Our discussion extends to the trends of how different substitute cations Mn2+, Li+, and Mg2+ impact the resonant properties, which suggests a guideline for designing antiferromagnetic THz materials.

DOI： 10.1103/PhysRevMaterials.4.074402

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevMaterials.4.074402/fulltext

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

We report an experimental observation of magnon-magnon coupling in interlayer exchange coupled synthetic antiferromagnets of FeCoB/Ru/FeCoB layers. An anticrossing gap of spin-wave resonance between acoustic and optic modes appears when the external magnetic field points to the direction tilted from the spin-wave propagation. The magnitude of the gap (i.e., coupling strength) can be controlled by changing the direction of the in-plane magnetic field and also enhanced by increasing the wave number of excited spin waves. We find that the coupling strength under the specified conditions is larger than the dissipation rates of both the resonance modes, indicating that a strong coupling regime is satisfied. A theoretical analysis based on the Landau-Lifshitz equation shows quantitative agreement with the experiments and indicates that the anticrossing gap appears when the exchange symmetry of two magnetizations is broken by the spin-wave excitation.

DOI： 10.1103/PhysRevLett.125.017203

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.125.017203/fulltext

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Electron and spin transport in chiral antiferromagnets are of great interest in both fundamental and application point of views. In this letter, we explore and compare spin transport properties of a chiral antiferromagnetic L12-ordered Mn3Ir and a disordered Mn3Ir by the spin pumping experiments. Larger Gilbert damping enhancement of the Fe20Ni80 was found in L12-ordered Mn3Ir/Fe20Ni80 and L12-ordered Mn3Ir/Ti/Fe20Ni80 multilayers comparing to those with disordered ones. Our results suggest that the chiral spin structure causes larger spin dissipation than disordered spin structure.

DOI： 10.35848/1882-0786/ab9876

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

In this study, we theoretically investigated properties of magnetostatic spin waves in rare-earth and transition-metal ferrimagnets with various angular momentum. The resonant frequency of high-(low-) frequency mode has the lowest (highest) value at angular momentum compensation temperature (T A). It was found that both resonance modes show a maximum group velocity at T A. Furthermore, the low-frequency mode shows higher group velocity than the high-frequency mode at any temperature. Our findings are the key to advance both the physics and the technology to develop research field of magnonics based on the antiferromagnetic spin waves.

DOI： 10.35848/1882-0786/ab916d

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We investigated caustic-like spin wave beams radiated from a narrow waveguide to a continuous film using a Permalloy. For this purpose, we developed a spatially resolved optical heterodyne detection of propagating spin waves by using the polar Kerr effect, which allows the measurement of the intensity and the phase information of the spin waves. We characterized magnetostatic surface spin wave modes in one-dimensional (1D) propagation and caustic-like spin wave beams in two-dimensional (2D) propagation as a function of excitation frequency. The fast Fourier transformations of the real space images reconstruct 1D and 2D spin wave dispersion, which agree with the theoretical calculations.

DOI： 10.1063/5.0010410

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Magnetic-field-induced domain reversal mechanisms of antiferromagnetic (AF) NiO thin films are investigated by spin Hall magnetoresistance (SMR) measurements. The field strength dependence of SMR amplitudes is measured in epitaxial and polycrystalline NiO films. From the field-dependent behavior of SMR amplitude, two distinct domain reversal mechanisms are found for those NiO films. In the epitaxial films, the conventional monodomain formation against the destressing field due to the magneto-elastic coupling is observed. On the other hand, the thermally assisted domain reversal is dominant in the polycrystalline films. Based on our thermal assisted model, the effective values of domain pinning potential and the number of spins contributing to domain reversal in polycrystalline films are determined. These values are quite important to design AF spin memory devices. This study contributes to building a method to determine the key parameters in AF spintronics with polycrystalline thin films, which are free from the lattice mismatching problem.

DOI： 10.1063/1.5142495

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Science Advances  

The nonreciprocity of propagating spin waves, i.e., the difference in amplitude and/or frequency depending on the propagation direction, is essential for the realization of spin wave-based logic circuits. However, the nonreciprocal frequency shifts demonstrated so far are not large enough for applications because they originate from interfacial effects. In addition, switching of the spin wave nonreciprocity in the electrical way remains a challenging issue. Here, we show a switchable giant nonreciprocal frequency shift of propagating spin waves in interlayer exchange-coupled synthetic antiferromagnets. The observed frequency shift is attributed to large asymmetric spin wave dispersion caused by a mutual dipolar interaction between two magnetic layers. Furthermore, we find that the sign of the frequency shift depends on relative configuration of two magnetizations, based on which we demonstrate an electrical switching of the nonreciprocity. Our findings provide a route for switchable and highly nonreciprocal spin wave-based applications.

DOI： 10.1126/sciadv.aaz6931

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Applied  

The interface between a magnetic material and a heavy metal that has a large spin-orbit interaction is at the root of various spin-related phenomena. In this paper, we address the peculiar spin-dependent transport at a Pt/Cr2O3 interface by exploring the origin of the nonlinear anomalous Hall effect (AHE) in Pt/Cr2O3 bilayers. X-ray magnetic circular dichroism (XMCD) measurements show no appreciable magnetic moment at the interface originating from Cr 3d and Pt 5d orbitals, which could be associated with the AHE response. A possible interfacial magnetic moment M at the Pt/Cr2O3 interface, assumed from the detection limit of the XMCD measurements, yields an anomalous Hall conductivity (σAHE) per unit net magnetic moment (M),-σAHE/M, of 0.57 V-1, which is extraordinary large compared with that for general magnetic materials. Together with first-principles calculations, the results suggest the possibility of an intrinsic AHE in the Pt/Cr2O3 interface that does not rely on the net magnetic moment.

DOI： 10.1103/PhysRevApplied.13.034052

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

In this paper, we investigate the enhancement of the antiferromagnetic damping in the sintered NiO-HM (where HM is heavy metal) granular systems having NiO/HM interfaces, where HM=Pt or Pd. Under the assumption of the spin pumping model, we derive the effective interfacial damping conductance geff, the parameter which characterizes the upper-bound estimate of the spin pumping effect, to be 12±1nm-2 and 5±1nm-2 for the NiO/Pt and the NiO/Pd interfaces, respectively, at room temperature. geff experimentally derived in this study are an important milestone in antiferromagnetic spintronics, giving a guideline for various spin current transfer and spin interaction phenomena with antiferromagnets where the spin mixing conductance is involved.

DOI： 10.1103/PhysRevB.101.060402

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

We investigated the field-sweep-rate and time dependence of the transverse resistivity anomalies in ultrathin SrRuO3 epitaxial thin films the behaviors of which resemble what has been claimed to be the topological Hall effect. We find that the magnitudes of the anomalies are independent of the field sweep rate, while the magnetic field at which the anomalies appear (Hhump) and the coercive field (Hc) exhibit identical sweep-rate dependence. We also show that the transverse resistivity under a fixed external magnetic field exhibits transient behavior, eventually (≈5000 s) approximating the value of the anomalous Hall resistivity that is obtained after the magnetization reversal processes are completed. These results indicate that Hc is inhomogeneous within the films and activation energies of the magnetization reversal at Hhump and Hc are identical. The observed field-sweep-rate and time dependence of the transverse resistivity anomalies can be understood in the framework of conventional magnetic switching dynamics, and topological interpretation would not be necessarily taken into account. Our results are in line with a model in which inhomogeneity of Hc and anomalous Hall resistivity are responsible for the transverse resistivity anomalies in SrRuO3.

DOI： 10.1103/PhysRevB.101.014448

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Antiferromagnets having negligible net magnetization but a topologically nontrivial spin structure are a good testbed for investigating the intrinsic anomalous Hall effect (AHE). In this Letter, we explore L12-ordered Mn3Ir thin films, which are one of the noncollinear antiferromagnets predicted to exhibit the intrinsic AHE due to their topologically nontrivial spin structure. The anomalous Hall conductivity as large as σAHE = 40 ω-1 cm-1 was observed at R.T. This value can be translated to the anomalous Hall conductivity per net magnetization M as |σAHE/M| = 0.6 V-1, which is much larger compared to those for general ferromagnetic materials. We also show that σAHE depends on the crystallinity of Mn3Ir as well as the chemical order parameter S characterizing a content of the L12 phase. Our results experimentally verify that L12-ordered Mn3Ir thin films exhibit the topologically originated AHE.

DOI： 10.1063/1.5128241

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Tungsten thin films are used for various applications and sometimes exhibit an A15 structure (β-W). They have some superior properties in comparison to the bcc structure (α-W), such as a higher superconducting transition temperature and larger spin Hall angle. However, elastic constants of β-W are unclear, which restricts mechanical applications and reliable density-functional-theory calculations. In this study, we synthesized α-W, β-W, and mixed-phase W films and determined their elastic constants by picosecond ultrasonics. We also calculated the elastic constants based on density functional theory and reveal that β-W has a larger elastic anisotropy and smaller shear modulus. Our calculation further indicates a stable stacking faulted β-W, which leads to a monoclinic structure.

DOI： 10.1063/1.5131768

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Magnetics Society of Japan  

We developed ferrimagnetic [Co(0.5)/Gd(1)/Pt(1)]N (unit: nm) multilayers with structural inversion symmetry breaking and investigated the dependence of magnetic properties and magnetic domain structures on the repetition number (N = 1 – 50). The magnetization compensation temperature increases as N increases, and saturates at around 210 K for N ≥ 20. All films with various repetition number possess the out-of-plane magnetic easy axis, and multi domain structure at the remanence state was observed in the film with N = 50. These results show that the magnetic properties of the ferrimagnetic Co/Gd/Pt multilayers can be tuned by the repetition number.

DOI： 10.3379/msjmag.2001R002

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出版者・発行元：Japan Society of Applied Physics  

Spin Hall magnetoresistance has been used to probe magnetic moments in magnetic insulator/heavy metal thin films. Here we explore the magnetic field-dependent magnetoresistance and the temperature-dependent magnetoresistance in a Pt/CoO/Pt trilayer near the Neél temperature of CoO. The obtained magnetoresistance in an antiferromagnetic phase can be interpreted as SMR whereas the results in a paramagnetic one suggest the additional mechanism other than the conventional SMR.

DOI： 10.7567/1347-4065/ab6505

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review X  

As electrical control of Neél order opens the door to reliable antiferromagnetic spintronic devices, understanding the microscopic mechanisms of antiferromagnetic switching is crucial. Spatially resolved studies are necessary to distinguish multiple nonuniform switching mechanisms; however, progress has been hindered by the lack of tabletop techniques to image the Neél order. We demonstrate spin Seebeck microscopy as a sensitive tabletop method for imaging antiferromagnetism in thin films and apply this technique to study spin-torque switching in Pt/NiO and Pt/NiO/Pt heterostructures. We establish the interfacial antiferromagnetic spin Seebeck effect in NiO as a probe of surface Neél order. By imaging before and after applying current-induced spin torque, we resolve spin domain rotation and domain wall motion. We correlate the changes in spin Seebeck images with electrical measurements of the average Neél orientation through the spin Hall magnetoresistance, confirming that we image antiferromagnetic order.

DOI： 10.1103/physrevx.9.041016

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We provide a macroscopic theory and experimental results for magnetic resonances of antiferromagnetically-coupled ferrimagnets. Our theory, which interpolates the dynamics of antiferromagnets and ferromagnets smoothly, can describe ferrimagnetic resonances across the angular momentum compensation point. We also present experimental results for spin-torque induced ferrimagnetic resonance at several temperatures. The spectral analysis based on our theory reveals that the Gilbert damping parameter, which has been considered to be strongly temperature dependent, is insensitive to temperature. We envision that our work will facilitate further investigation of ferrimagnetic dynamics by providing a theoretical framework suitable for a broad range of temperatures.

DOI： 10.7567/1882-0786/ab33d5

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Electronics  

Antiferromagnetic materials offer ultrafast spin dynamics and could be used to build devices that are orders of magnitude faster than those based on ferromagnetic materials. Spin-transfer torque is key to the electrical control of spins and has been demonstrated in ferromagnetic spintronics. However, experimental exploration of spin-transfer torque in antiferromagnets remains limited, despite a number of theoretical studies. Here, we report an experimental examination of the effects of spin-transfer torque on the motion of domain walls in antiferromagnetically coupled ferrimagnets. Using a ferrimagnetic gadolinium–iron–cobalt (GdFeCo) alloy in which Gd and FeCo moments are coupled antiferromagnetically, we find that non-adiabatic spin-transfer torque acts like a staggered magnetic field, providing efficient control of the domain walls. We also show that the non-adiabaticity parameter of the spin-transfer torque is significantly larger than the Gilbert damping parameter, in contrast to the case of non-adiabatic spin-transfer torque in ferromagnets.

DOI： 10.1038/s41928-019-0303-5

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Recent advances in antiferromagnetic spin dynamics using rare-earth (RE) and transition-metal (TM) ferrimagnets have attracted much interest for spintronic devices with a high speed and density. In this study, the spin wave properties in the magnetostatic backward volume mode and surface mode in RE-TM ferrimagnetic Gd x Co1-x films with various composition x are investigated using spin wave spectroscopy. The obtained group velocity and attenuation length are well explained by the ferromagnet-based spin wave theory when the composition of Gd x Co1-x is far from the compensation point.

DOI： 10.7567/1347-4065/ab2f98

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We studied perpendicular magnetic anisotropy (PMA) and magnetization compensation temperature (T M) in Tb/CoFeB/MgO films. Interlayer antiferromagnetic coupling between Tb and CoFeB layers enables useful antiferromagnetic properties containing a CoFeB/MgO junctions, which are important for the practical applications to obtain giant tunnel magnetoresistance and voltage-control of magnetic anisotropy. While the PMA is mainly attributed to the interface at CoFeB/MgO, T M can be controlled by the thickness ratio of Tb and CoFeB layers as the magnetic moments of them are antiferromagnetically coupled. Our results provide many possibilities to add exciting new functions to ferrimagnetic spintronics.

DOI： 10.7567/1882-0786/ab2c23

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Materials  

Symmetry breaking is a fundamental concept that prevails in many branches of physics1–5. In magnetic materials, broken inversion symmetry induces the Dzyaloshinskii–Moriya interaction (DMI), which results in fascinating physical behaviours6–14 with the potential for application in future spintronic devices15–17. Here, we report the observation of a bulk DMI in GdFeCo amorphous ferrimagnets. The DMI is found to increase linearly with an increasing thickness of the ferrimagnetic layer, which is a clear signature of the bulk nature of DMI. We also found that the DMI is independent of the interface between the heavy metal and ferrimagnetic layer. This bulk DMI is attributed to an asymmetric distribution of the elemental content in the GdFeCo layer, with spatial inversion symmetry broken throughout the layer. We expect that our experimental identification of a bulk DMI will open up additional possibilities to exploit this interaction in a wide range of materials.

DOI： 10.1038/s41563-019-0380-x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

We systematically investigate the perpendicular magnetocrystalline anisotropy (MCA) in Co-Pt/Pd-based multilayers. Our magnetic measurement data show that the asymmetric Co/Pd/Pt multilayer has a significantly larger perpendicular magnetic anisotropy (PMA) energy compared to the symmetric Co/Pt and Co/Pd multilayer samples. We further support this experiment by first-principles calculations on CoPt2, CoPd2, and CoPtPd, which are composite bulk materials that consist of three atomic layers in a unit cell, Pt/Co/Pt, Pd/Co/Pd, and Pt/Co/Pd, respectively. By estimating the contribution of bulk spin-momentum coupling to the MCA energy, we show that the CoPtPd multilayer with symmetry breaking has a significantly larger PMA energy than the other multilayers that are otherwise similar but lack symmetry breaking. This observation thus provides evidence of the PMA enhancement due to the structural inversion symmetry breaking and highlights the asymmetric CoPtPd as an artificial magnetic material with bulk spin-momentum coupling, which opens a pathway toward the design of materials with strong PMA.

DOI： 10.1103/PhysRevB.99.180410

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Materials  

In antiferromagnetic spintronics where manipulation of the antiferromagnetic spins is a central technological challenge, it is important to understand the dynamic properties, especially their THz spin dynamics and the magnetic damping. Here, we investigate thoroughly the antiferromagnetic spin dynamics in NiO by broadband THz spectroscopy and find the remarkable difference in the damping constants α=5.0±0.4×10-4 and 7.4±0.4×10-4, respectively, for mono- and polycrystalline NiO, indicating the existence of strong extrinsic contributions to the damping, such as two-magnon scattering. Our results shed light on the mechanism of the antiferromagnetic dissipative dynamics and give important insights for developing antiferromagnetic and THz spintronics devices.

DOI： 10.1103/PhysRevMaterials.3.051402

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

We investigate the Gilbert damping parameter α for rare earth (RE)-transition metal (TM) ferrimagnets over a wide temperature range. Extracted from the field-driven magnetic domain-wall mobility, α was as low as the order of 10-3 and was almost constant across the angular momentum compensation temperature TA, starkly contrasting previous predictions that α should diverge at TA due to a vanishing total angular momentum. Thus, magnetic damping of RE-TM ferrimagnets is not related to the total angular momentum but is dominated by electron scattering at the Fermi level where the TM has a dominant damping role. This low value of the Gilbert damping parameter suggests that ferrimagnets can serve as versatile platforms for low-dissipation high-speed magnetic devices.

DOI： 10.1103/PhysRevLett.122.127203

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Nanotechnology  

In the presence of a magnetic field, the flow of charged particles in a conductor is deflected from the direction of the applied force, which gives rise to the ordinary Hall effect. Analogously, moving skyrmions with non-zero topological charges and finite fictitious magnetic fields exhibit the skyrmion Hall effect, which is detrimental for applications such as skyrmion racetrack memory. It was predicted that the skyrmion Hall effect vanishes for antiferromagnetic skyrmions because their fictitious magnetic field, proportional to net spin density, is zero. Here we investigate the current-driven transverse elongation of pinned ferrimagnetic bubbles. We estimate the skyrmion Hall effect from the angle between the current and the bubble elongation directions. The angle and, hence, the skyrmion Hall effect vanishes at the angular momentum compensation temperature where the net spin density vanishes. Furthermore, our study establishes a direct connection between the fictitious magnetic field and the spin density.

DOI： 10.1038/s41565-018-0345-2

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掲載種別：研究論文（学術雑誌）  

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Although bulk magnetic properties of various antiferromagnets have been vigorously studied since long ago, their properties in the form of thin films, which are more relevant to antiferromagnetic spintronic devices, have not been investigated as much. In this work, we characterized the Néel temperature of Cr 2 O 3 thin films by investigating the temperature dependence of the spin Hall magnetoresistance in Cr 2 O 3 /Pt bilayers. A precise determination of the Néel temperature was made possible by carefully designing the direction of the magnetic anisotropy in Cr 2 O 3 . The results provide a reliable way to determine the Néel temperature of antiferromagnetic thin films.

DOI： 10.1063/1.5082220

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Applied  

We investigate the temperature dependence of the magnetic damping in exchange-biased Pt/Fe50Mn50/Fe20Ni80/SiOx multilayers. In samples having a strong exchange bias, we observed a drastic decrease of the magnetic damping of Fe-Ni with increasing temperature up to the blocking temperature. The results essentially indicate that the nonlocal enhancement of the magnetic damping can be choked by the adjacent antiferromagnet and its temperature-dependent exchange bias. We also point out that such a strong temperature-dependent damping may be very beneficial for spintronic applications.

DOI： 10.1103/PhysRevApplied.11.011001

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We investigate temperature, temporal and magnetic-field dependence of unidirectional magnetoresistance (UMR) in metallic bilayers. The UMR is found to decrease rapidly with reducing temperature and converges to a finite value at low-temperature limit. The temporal dependence shows that the UMR emerges in a nanosecond time scale, which depends on the current amplitude. The magnetic-field dependence shows that the UMR is almost constant up to 5 T. These experimental results imply that the high-energy magnons, which are not considered in existing theory, can be involved in the observed UMR. Our results therefore suggest that a more extended theory is required for the complete understanding of UMR.

DOI： 10.7567/1882-0786/ab1b54

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出版者・発行元：Journal of the Magnetics Society of Japan  

Nb, V, and Ta are all well-known superconducting elements in a simple substance. We report the superconductivity of Nb/V/Ta superlattices sputtered onto MgO(100) substrates, in which global inversion symmetry was broken along the stacking direction. It was found that the superlattices had long-range crystalline coherence with the well-defined periodicity of the constituent layers, and they exhibited superconducting transition despite the thicknesses of the layers.

DOI： 10.3379/msjmag.1903L001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

There is a need to control magnetic properties at a desired location in a magnetic film towards a realization of fundamental devices, such as domain wall logic or magnonic applications. Here, we demonstrate the formation of a magnetic domain structure at a desired location in a Pt/Co film, using electrical gating with a meshed gate electrode and sweeping the applied magnetic field. As the magnetic properties can be changed by modulating the electron density at the surface of the Co layer, this method in principle provides higher speed and power-efficient operation in inducing a nanoscale domain structure or in configuring a volatile magnonic crystal.

DOI： 10.1063/1.5078553

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

We clarify the physical origin of anomalies in transverse resistivity often observed in exotic materials, such as SrRuO3, in which the Berry curvature is manifested in the transport properties. The previously attributed mechanism for the anomalies, the topological Hall effect (THE) [e.g., J. Matsuno et al., Sci. Adv. 2, e160030 (2016)10.1126/sciadv.1600304], is refuted by our thorough investigations as well as formulation of a model considering inhomogeneous magnetoelectric properties in the material. Our analyses fully explain every feature of the anomalies without resorting to the THE. The present results establish a fundamental understanding, which was previously overlooked, of magnetotransport properties in such exotic materials.

DOI： 10.1103/physrevb.98.180408

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.98.180408/fulltext

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Magnetics Society of Japan  

We report on magnetoresistance measurements in a heavy metal/ Mn3Ir multilayers. After a post annealing process, we observed the magnetoresistance associated with the ordered crystalline structure of the Mn3Ir. The resistance change as a function of the strength as well as the direction of the applied field suggests that the magnetoresistance is partially related to a modification of the Néel order by the magnetic field. Our further detailed investigation revealed that there is an additional component of the resistance change, perhaps due to the non-collinear magnetic structure associated with the L12-ordered Mn3Ir, which cannot be accounted for by any conventional magnetoresistance effects.

DOI： 10.3379/msjmag.1901R001

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

In this Letter, we show the demonstration of a sequential antiferromagnetic memory operation with a spin-orbit-torque write, by the spin Hall effect, and a resistive read in the CoGd synthetic antiferromagnetic bits, in which we reveal the distinct differences in the spin-orbit-torque and field-induced switching mechanisms of the antiferromagnetic moment, or the Néel vector. In addition to the comprehensive spin torque memory operation, our thorough investigations also highlight the high immunity to a field disturbance as well as a memristive behavior of the antiferromagnetic bits.

DOI： 10.1103/PhysRevLett.121.167202

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その他リンク： http://orcid.org/0000-0001-7071-0823

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Spin current transmission in antiferromagnetic materials is one of the important and intriguing problems in the recently emerged field of antiferromagnetic spintronics. We investigate the spin current transmission in polycrystalline NiO by referencing the effective Gilbert damping constant in NiO/FeNi bilayers. The results are discussed with reference to the spin pumping theory assuming that the NiO layer is spin diffusive. We extracted the spin diffusion length of >22 nm for the NiO and the mixing conductance of >6 nm%2 at the NiO/FeNi interface. The obtained spin diffusion length and the mixing conductance are within reasonable ranges compared with previous reports.

DOI： 10.7567/APEX.11.073003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

The Curie temperature TC is one of the most fundamental physical properties of ferromagnetic materials and can be described by the Weiss molecular field theory with the exchange interaction of neighboring atoms. Here, we demonstrate the electrical control of exchange coupling in cobalt films through direct magnetization measurements. We find that the reduction in magnetization with temperature, which is caused by thermal spin wave excitation and scales with Bloch’s law, clearly depends on the applied electric field. Furthermore, we confirm that the correlation between the electric-field-induced modulation of TC and that of exchange coupling follows the Weiss molecular field theory.

DOI： 10.7567/APEX.11.073002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

The domain-wall (DW) motion of ferrimagnets is investigated with respect to the angular-momentum-compensation temperature TA for a wide range of magnetic fields μ0Hz, ranging from the depinning to flow regimes. While the DW velocity v exhibits a maximum at TA in the flow regime regardless of μ0Hz, the temperature at which v is maximized depends on μ0Hz because of the temperature dependence of the depinning field μ0Hdep, causing difficulty in determining TA. To solve this problem, we propose a reduced coordinate μ0Hz % μ0Hdep, which reveals that v is maximized at TA even in the depinning regime. Our work suggests that μ0Hdep should be identified prior to determining TA.

DOI： 10.7567/APEX.11.063001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Electric-field modulations of magnetic properties have been extensively studied not only for practical applications but also for fundamental interest. In this study, we investigated the electric field effect on the exchange interaction in ultrathin Co films with ionic liquids. The exchange coupling J was characterized from the direct magnetization measurement as a function of temperature using Pt/ultrathin Co/MgO structures. The trend of the electric field effect on J is in good agreement with that of the theoretical prediction, and a large change in J by applying a gate voltage was observed by forming an electric double layer using ionic liquids.

DOI： 10.7567/APEX.11.063002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We report a systematic experimental study on the refraction and reflection of magnetostatic spin-waves at a thickness step between two Permalloy films of different thickness. The transmitted spin-waves for the transition from a thick film to a thin film have a higher wave vector compared to the incoming waves. Consequently, such systems may find use as passive wavelength transformers in magnonic networks. We investigate the spin-wave transmission behavior by studying the influence of the external magnetic field, incident angle, and thickness ratio of the films using time-resolved scanning Kerr microscopy and micro-focused Brillouin light scattering.

DOI： 10.7567/APEX.11.053002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Ferromagnetic resonance (FMR) is one of the most popular techniques to characterize dynamic properties of ferromagnetic materials. Among various FMR measurement techniques, the homodyne FMR detection has been frequently used to characterize thin-film ferromagnetic multilayers owing to its high sensitivity. However, a drawback of this technique was considered to be the requirement for a structural inversion asymmetry, which makes it unsuitable to characterize a single layer of ferromagnet. In this study, we demonstrate a homodyne FMR detection of the Kittel’s mode FMR dynamics of a single layer of FeNi by creating a non-uniform radio-frequency excitation current.

DOI： 10.7567/APEX.11.053008

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

We propose an alternative method of determining the magnetic anisotropy field μ0HK in ferro-/ferrimagnets. On the basis of the droplet nucleation model, there exists linearity between domain-wall (DW) energy density and in-plane magnetic field. We find that the slope is simply represented by μ0HK and Dzyaloshinskii–Moriya interaction (DMI). By measuring the in-plane magnetic field dependence of the coercivity field, closely corresponding to the DW energy density, a robust value for μ0HK can be quantified. This robust value can be used to determine μ0HK over a wide range of values, overcoming the limitations caused by the small strength of the external magnetic field typically used in experiments.

DOI： 10.7567/JJAP.57.050308

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

Chiral spin textures of a ferromagnetic layer in contact to a heavy non-magnetic metal, such as Néel-type domain walls and skyrmions, have been studied intensively because of their potential for future nanomagnetic devices. The Dyzaloshinskii-Moriya interaction (DMI) is an essential phenomenon for the formation of such chiral spin textures. In spite of recent theoretical progress aiming at understanding the microscopic origin of the DMI, an experimental investigation unravelling the physics at stake is still required. Here we experimentally demonstrate the close correlation of the DMI with the anisotropy of the orbital magnetic moment and with the magnetic dipole moment of the ferromagnetic metal in addition to Heisenberg exchange. The density functional theory and the tight-binding model calculations reveal that inversion symmetry breaking with spin-orbit coupling gives rise to the orbital-related correlation. Our study provides the experimental connection between the orbital physics and the spin-orbit-related phenomena, such as DMI.

DOI： 10.1038/s41467-018-04017-x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The influence of temperature on the magnetic-field-driven domain wall motion is investigated in GdFeCo ferrimagnets with perpendicular magnetic anisotropy (PMA). We find that the depinning field strongly depends on temperature. Moreover, it is also found that the saturation magnetization exhibits a similar dependence on temperature to that of the depinning field. From the creep-scaling criticality, a simple relation between the depinning field and the properties of PMA is clearly identified theoretically as well as experimentally. Our findings open a way for a better understanding of how the magnetic properties influence the depinning field in the magnetic system and would be valuably extended to depinning studies in other systems.

DOI： 10.1063/1.5022809

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

Electric field effects on magnetism in metals have attracted widespread attention, but the microscopic mechanism is still controversial. We experimentally show the relevancy between the electric field effect on magnetism and on the electronic structure in Pt in a ferromagnetic state using element-specific measurements: x-ray magnetic circular dichroism (XMCD) and x-ray absorption spectroscopy (XAS). Electric fields are applied to the surface of ultrathin metallic Pt, in which a magnetic moment is induced by the ferromagnetic proximity effect resulting from a Co underlayer. XMCD and XAS measurements performed under the application of electric fields reveal that both the spin and orbital magnetic moments of Pt atoms are electrically modulated, which can be explained not only by the electric-field-induced shift of the Fermi level but also by the change in the orbital hybridizations.

DOI： 10.1103/PhysRevLett.120.157203

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Reviews of Modern Physics  

Antiferromagnetic materials could represent the future of spintronic applications thanks to the numerous interesting features they combine: they are robust against perturbation due to magnetic fields, produce no stray fields, display ultrafast dynamics, and are capable of generating large magnetotransport effects. Intense research efforts over the past decade have been invested in unraveling spin transport properties in antiferromagnetic materials. Whether spin transport can be used to drive the antiferromagnetic order and how subsequent variations can be detected are some of the thrilling challenges currently being addressed. Antiferromagnetic spintronics started out with studies on spin transfer and has undergone a definite revival in the last few years with the publication of pioneering articles on the use of spin-orbit interactions in antiferromagnets. This paradigm shift offers possibilities for radically new concepts for spin manipulation in electronics. Central to these endeavors are the need for predictive models, relevant disruptive materials, and new experimental designs. This paper reviews the most prominent spintronic effects described based on theoretical and experimental analysis of antiferromagnetic materials. It also details some of the remaining bottlenecks and suggests possible avenues for future research. This review covers both spin-transfer-related effects, such as spin-transfer torque, spin penetration length, domain-wall motion, and "magnetization" dynamics, and spin-orbit related phenomena, such as (tunnel) anisotropic magnetoresistance, spin Hall, and inverse spin galvanic effects. Effects related to spin caloritronics, such as the spin Seebeck effect, are linked to the transport of magnons in antiferromagnets. The propagation of spin waves and spin superfluids in antiferromagnets is also covered.

DOI： 10.1103/RevModPhys.90.015005

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Spin injection into 3d transition metals and their alloys has been investigated intensively in recent years. In this study, we focus on the FeRh alloy, which is often used in the context of antiferromagnetic spintronics. We explore the interaction between the spin current and magnetic moments in FeRh by means of spin-torque ferromagnetic resonance. We obtain a spin Hall efficiency of ξSH = 24 ± 3%, which indicates that the spin current from Pt interacts with the magnetic moments in FeRh.

DOI： 10.7567/APEX.11.013008

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Scientific Reports  

For a long time, there were no efficient ways of controlling antiferromagnets. Quite a strong magnetic field was required to manipulate the magnetic moments because of a high molecular field and a small magnetic susceptibility. It was also difficult to detect the orientation of the magnetic moments since the net magnetic moment is effectively zero. For these reasons, research on antiferromagnets has not been progressed as drastically as that on ferromagnets which are the main materials in modern spintronic devices. Here we show that the magnetic moments in NiO, a typical natural antiferromagnet, can indeed be controlled by the spin torque with a relatively small electric current density (~4 × 107 A/cm2) and their orientation is detected by the transverse resistance resulting from the spin Hall magnetoresistance. The demonstrated techniques of controlling and detecting antiferromagnets would outstandingly promote the methodologies in the recently emerged “antiferromagnetic spintronics”. Furthermore, our results essentially lead to a spin torque antiferromagnetic memory.

DOI： 10.1038/s41598-018-32508-w

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

In optics, a light beam experiences a spatial shift in the beam plane upon total internal reflection. This shift is usually referred to as the Goos-Hänchen shift. When dealing with plane waves, it manifests itself as a phase shift between an incoming and reflected wave that depends on the wave vector component along the interface. In the experiments presented here, plane spin waves are excited in a 60-nm-thick Permalloy film and propagate towards the edge of the film. By means of time-resolved scanning Kerr microscopy, we are able to directly detect a phase shift between the incoming and reflected wave. With the help of a numerical model, we show that this phase shift naturally occurs for spin waves in the dipolar regime.

DOI： 10.1103/PhysRevLett.121.137201

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

In this study, we investigated the electric field effect on interfacial perpendicular magnetic anisotropy (i-PMA) and interfacial Dzyaloshinskii-Moriya interaction (i-DMI) by propagating spin wave spectroscopy with a high degree of accuracy in Pt/Co/MgO structures. We estimated i-PMA and i-DMI energy densities of 0.71 and 0.45mJ/m2 from the nonreciprocity of spin wave propagation, and the electric field effect on them of 2.5 and 2.0 fJ/(V&m) from symmetrical and asymmetrical electrical modulations of the spin wave frequency depending on the propagation direction. We also discussed the possibility of an electric-field-controlled phase shifter for spin wave logic devices.

DOI： 10.7567/JJAP.57.080309

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

Spin interaction in antiferromagnetic materials is of central interest in the recently emerging antiferromagnetic spintronics. In this Letter, we explore the spin current interaction in antiferromagnetic FeMn by the spin pumping effect. Exchange biased FeNi/FeMn films, in which the Néel vector can be presumably controlled via the exchange spring effect, are employed to investigate the damping enhancement depending on the relative orientation between the Néel vector and the polarization of the pumped spin current. The correlation between the enhanced damping and the strength of the exchange bias suggests that the twisting of the Néel vector induces an additional spin dissipation, which verifies that the Slonczewski-type spin torque is effective even in antiferromagnetic materials.

DOI： 10.1103/PhysRevLett.119.267204

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

We fabricated electric-field-effect transistor structures with a channel layer of an itinerant ferromagnet SrRuO 3 (SRO) heterostructured with a cap layer of BaTiO 3 and investigated the electric field effects on the anomalous Hall effect (AHE) in SRO. We show that by applying positive and negative gate voltages (VG), the anomalous Hall conductivity in the heterostructured SRO increases and decreases, respectively, regardless of its sign, while no change in the magnetic easy axis direction is observed. The results indicate that the observed VG-induced modulations of the AHE do not simply originate from changes in the magnetization and magnetic anisotropy and indicate that VG-induced changes in an integral of the Berry curvature over the filled electronic states play a key role in the observed electric field effects on the AHE in SRO. We also found that VG-induced modulations on the AHE are negligibly small for transistor structures with a SRO channel having no BTO cap layer. This implies that the cap-layer-induced modifications in the Ru-O-Ru bond angles in the channel affect the Berry phase, enhancing the electric field effects on the AHE in SRO.

DOI： 10.1103/PhysRevB.96.214422

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Materials  

Antiferromagnetic spintronics is an emerging research field which aims to utilize antiferromagnets as core elements in spintronic devices. A central motivation towards this direction is that antiferromagnetic spin dynamics is expected to be much faster than its ferromagnetic counterpart. Recent theories indeed predicted faster dynamics of antiferromagnetic domain walls (DWs) than ferromagnetic DWs. However, experimental investigations of antiferromagnetic spin dynamics have remained unexplored, mainly because of the magnetic field immunity of antiferromagnets. Here we show that fast field-driven antiferromagnetic spin dynamics is realized in ferrimagnets at the angular momentum compensation point T A. Using rare earth-3d-transition metal ferrimagnetic compounds where net magnetic moment is nonzero at T A, the field-driven DW mobility is remarkably enhanced up to 20 km s â 1 T â 1. The collective coordinate approach generalized for ferrimagnets and atomistic spin model simulations show that this remarkable enhancement is a consequence of antiferromagnetic spin dynamics at T A. Our finding allows us to investigate the physics of antiferromagnetic spin dynamics and highlights the importance of tuning of the angular momentum compensation point of ferrimagnets, which could be a key towards ferrimagnetic spintronics.

DOI： 10.1038/nmat4990

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

The asymmetric magnetoresistance (MR) in Py/Pt bilayers is investigated. It increases linearly with respect to the current density up to a threshold and increases more rapidly above this threshold. To reveal the origin of the threshold behavior, we investigate the magnetic field dependence of the asymmetric MR. It is found that the magnetic field strongly suppresses the asymmetric MR only above the threshold current density. Micromagnetic simulation reveals that the reduction of magnetization due to the spin-torque oscillation can be the origin of the threshold behavior of the asymmetric MR.

DOI： 10.7567/APEX.10.073001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We study the perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO bilayers in contact with W, Ta, IrMn, and Ti, which have been suggested for use as the spin-orbit-torque-related underlayers. The saturation magnetization of CoFeB depends on the underlayer material used owing to the formation of a dead layer that affects the PMA strength of each film. The X-ray magnetic circular dichroism measurement reveals that interfacial intermixing suppresses only the perpendicular orbital moment of Fe, whereas it simultaneously suppresses both the perpendicular and in-plane orbital moments of Co.

DOI： 10.7567/APEX.10.073006

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Harmonic Hall measurements were performed in Pt/GdFeCo bilayers to quantify the effective field resulting from the spin-orbit torque at various temperatures, both above and below the magnetization compensation temperature (TM). We found that the damping-like torque rapidly increased near the TM of the GdFeCo, which was attributed to a reduction in the net magnetic moment. Moreover, most importantly, the resulting spin Hall efficiency turned out to be constant across the temperature range.

DOI： 10.1063/1.4985436

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

We investigate the effect of the Dzyaloshinskii-Moriya interaction (DMI) on magnetic domain nucleation in a ferromagnetic thin film with perpendicular magnetic anisotropy. We propose an extended droplet model to determine the nucleation field as a function of the in-plane field. The model can explain the experimentally observed nucleation in a Co/Ni microstrip with an interfacial DMI. The results are also reproduced by micromagnetic simulation based on the string model. The electrical measurement method proposed here can be widely used to quantitatively determine the DMI energy density.

DOI： 10.1103/PhysRevB.95.220402

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

A creep motion of the magnetic domain wall (DW) in a perpendicularly magnetized Co wire, where the DW energy is artificially varied by applying a sloped electric field, is studied. Under the sloped electric field and a constant external magnetic field, the DW velocity gradually changes according to the position of the wire owing to the spatially varying DW energy. Although the sloped DW energy can be a source to drive a DW, no clear electric-field-induced DW motion is observed, most likely because the effective magnetic field induced by the sloped electric field is very small in the present system.

DOI： 10.7567/JJAP.56.050305

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We present an energy-efficient magnetic domain-writing scheme for domain wall (DW) motion-based memory devices. A cross-shaped nanowire is employed to inject a domain into the nanowire through current-induced DW propagation. The energy required for injecting the magnetic domain is more than one order of magnitude lower than that for the conventional field-based writing scheme. The proposed scheme is beneficial for device miniaturization because the threshold current for DW propagation scales with the device size, which cannot be achieved in the conventional field-based technique.

DOI： 10.7567/APEX.10.043002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

The electric field control of superparamagnetism is realized using a Cu/Ni system, in which the deposited Ni shows superparamagnetic behavior above the blocking temperature. An electric double-layer capacitor (EDLC) with the Cu/Ni electrode and a nonmagnetic counter electrode is fabricated to examine the electric field effect on magnetism in the magnetic electrode. By changing the voltage applied to the EDLC, the blocking temperature of the system is clearly modulated.

DOI： 10.7567/APEX.10.013004

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/S00540-016-2284-0

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/J.INTERMET.2017.01.004

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掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

We investigate the temperature dependence of the spin Hall magnetoresistance (SMR) in a W/CoFeB bilayer. The SMR is found to increase with decreasing temperature. An analysis based on the SMR theory suggests that the spin Hall angle of W and/or the spin polarization of CoFeB can be the origin of the temperature dependence of the SMR. We also find that the spin diffusion length and the resistivity of W do not significantly vary with temperature, which indicates the necessity of further study on the electron transport mechanism in W films to reveal the origin of the spin Hall effect in W.

DOI： 10.7567/JJAP.55.080308

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

The temperature dependence of magnetoresistance is investigated in ferrimagnetic GdFeCo/Pt heterostructures. An anomalous Hall effect (AHE) shows a monotonic behavior in temperature even across the magnetization compensation temperature TM, implying that the FeCo moment is responsible for the magnetotransport properties. An anisotropic magnetoresistance (AMR) exhibits a steep increase at low temperatures, which we ascribe to the contribution of a weak antilocalization in an amorphous GdFeCo layer. A spin Hall magnetoresistance (SMR) is found to exist in ferrimagnet/Pt systems and shows a moderate temperature dependence, in contrast to the SMR in YIG/Pt where a significant temperature dependence was observed. These results provide a basic understanding of the magnetotransport in amorphous ferrimagnets/heavy metal heterostructures.

DOI： 10.7567/APEX.9.073001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The electric field (EF) effect on the magnetic domain structure of a Pt/Co system was studied, where an EF was applied to the top surface of the Co layer. The width of the maze domain was significantly modified by the application of the EF at a temperature slightly below the Curie temperature. After a detailed analysis, a change in the microscopic exchange stiffness induced by the EF application was suggested to dominate the modulation of the domain width observed in the experiment. The accumulation of electrons at the surface of the Co layer resulted in an increase in the microscopic exchange stiffness and the Curie temperature. The result was consistent with the recent theoretical prediction.

DOI： 10.1063/1.4955265

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

We report the experimental observation of Snell's law for magnetostatic spin waves in thin ferromagnetic Permalloy films by imaging incident, refracted, and reflected waves. We use a thickness step as the interface between two media with different dispersion relations. Since the dispersion relation for magnetostatic waves in thin ferromagnetic films is anisotropic, deviations from the isotropic Snell's law known in optics are observed for incidence angles larger than 25° with respect to the interface normal between the two magnetic media. Furthermore, we can show that the thickness step modifies the wavelength and the amplitude of the incident waves. Our findings open up a new way of spin wave steering for magnonic applications.

DOI： 10.1103/PhysRevLett.117.037204

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Exchange bias is a unidirectional magnetic anisotropy developed in a bilayer of ferromagnetic and antiferromagnetic layers. Its technical importance as a "fix layer" is seen in various spintronic devices. The exchange bias can also be a probe to investigate the antiferromagnetic layer as it partly reflects the magnetic state of the antiferromagnet. In this work, we investigated the modulation of the exchange bias by a flow of electric current in Pt/Fe50Mn50/FeNi and Cu/Fe50Mn50/FeNi. We show that the exchange bias can be modulated just by applying the current due to interplay among the Joule heating, Ampere field, and current-induced effective field.

DOI： 10.7567/JJAP.55.070304

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Electric field effect on magnetism is an appealing technique for manipulating magnetization at a low energy cost. Here, we show that the local magnetization of an ultrathin Co film can be switched by simply applying a gate electric field without the assistance of any external magnetic field or current flow. The local magnetization switching is explained by nucleation and annihilation of magnetic domains through domain wall motion induced by the electric field. Our results lead to external-field-free and ultralow-energy spintronic applications.

DOI： 10.7567/APEX.9.063004

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Status Solidi (B) Basic Research  

We report the observation of a magnon Hall-like effect for the scattering of magnons at the sample edge in Y3Fe5O12 crystals. The experiments are performed under an out-of-plane magnetic field at room temperature using an infrared thermometry. When the magnons are incident into the sample edge in the unsaturated magnetic structure, appreciable transverse thermal gradient is detected. This thermal gradient could be attributed to magnon Hall effect for sample-edge scattering. We unexpectedly find that this effect is largely enhanced in the unsaturated regime, compared with the saturated regime where theoretical mechanism of magnon Hall effect due to the Berry curvature has been proposed previously.

DOI： 10.1002/pssb.201552520

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：APL Materials  

The dynamics of a magnetic domain wall (DW) under a transverse magnetic field Hy are investigated in two-dimensional (2D) Co/Ni microstrips, where an interfacial Dzyaloshinskii-Moriya interaction (DMI) exists with DMI vector D lying in +y direction. The DW velocity exhibits asymmetric behavior for ±Hy; that is, the DW velocity becomes faster when Hy is applied antiparallel to D. The key experimental results are reproduced in a 2D micromagnetic simulation, which reveals that the interfacial DMI suppresses the periodic change of the average DW angle φ even above the Walker breakdown and that Hy changes φ, resulting in a velocity asymmetry. This suggests that the 2D DW motion, despite its microscopic complexity, simply depends on the average angle of the DW and thus can be described using a one-dimensional soliton model. These findings provide insight into the magnetic DW dynamics in 2D systems, which are important for emerging spin-orbitronic applications.

DOI： 10.1063/1.4944897

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We investigate the noise in single layer graphene devices from equilibrium to far-from equilibrium and found that the 1/f noise shows an anomalous dependence on the source-drain bias voltage (VSD). While the Hooge's relation is not the case around the charge neutrality point, we found that it is recovered at very low VSD region. We propose that the depinning of the electron-hole puddles is induced at finite VSD, which may explain this anomalous noise behavior.

DOI： 10.1063/1.4943642

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Physics  

Topological defects such as magnetic solitons, vortices and skyrmions have started to play an important role in modern magnetism because of their extraordinary stability, which can be exploited in the production of memory devices. Recently, a type of antisymmetric exchange interaction, namely the Dzyaloshinskii-Moriya interaction (DMI; refs,), has been uncovered and found to influence the formation of topological defects. Exploring how the DMI affects the dynamics of topological defects is therefore an important task. Here we investigate the dynamics of the magnetic domain wall (DW) under a DMI by developing a real time DW detection scheme. For a weak DMI, the DW velocity increases with the external field and reaches a peak velocity at a threshold field, beyond which it abruptly decreases. For a strong DMI, on the other hand, the velocity reduction is completely suppressed and the peak velocity is maintained constant even far above the threshold field. Such a distinct trend of the velocity can be explained in terms of a magnetic soliton, the topology of which is protected during its motion. Our results therefore shed light on the physics of dynamic topological defects, which paves the way for future work in topology-based memory applications.

DOI： 10.1038/NPHYS3535

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/J.JSS.2015.10.036

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/S40560-016-0164-1

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

Coherent gigahertz-frequency surface acoustic waves (SAWs) traveling on the surface of a piezoelectric crystal can, via the magnetoelastic interaction, resonantly excite traveling surface spin waves in an adjacent thin-film ferromagnet. These excited surface spin waves, traveling with a definite in-plane wave-vector q∥ enforced by the SAW, can be detected by measuring changes in the electro-acoustical transmission of a SAW delay line. Here, we provide a demonstration that such measurements constitute a precise and quantitative technique for spin-wave spectroscopy, providing a means to determine both isotropic and anisotropic contributions to the spin-wave dispersion and damping. We demonstrate the effectiveness of this spectroscopic technique by measuring the spin-wave properties of a Ni thin film for a large range of wave vectors, | q ∥ | = 2.5 × 104-8 × 104cm-1, over which anisotropic dipolar interactions vary from being negligible to quite significant.

DOI： 10.1063/1.4938390

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Spin motive force (SMF) is induced by a time and spatial derivative of magnetizations and is dependent on spin polarization. We compare the SMF in FeNi with positive spin polarization with that in a magnetite (Fe3O4) with negative spin polarization. We observe the SMF induced by a nonuniform ferromagnetic resonance in Fe3O4 and find that the SMF in Fe3O4 is opposite to that in FeNi. This result originates from the negative spin polarization of Fe3O4. Our clear observation of the SMF depending on the sign of the spin polarization agrees well with the framework of the SMF theory.

DOI： 10.7567/APEX.8.123001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

We investigate the influence of the interfacial Dzyaloshinskii-Moriya interaction (DMI) on the propagation of Damon-Eshbach spin waves in micrometer-sized Pt(2 nm)/Co(0.4 nm)/Py(5 nm)/MgO(5 nm) stripes. We use time-resolved scanning Kerr microscopy to image the spin waves excited by a microwave antenna and to directly access their dispersion. The presence of an interfacial DMI manifests itself in an asymmetry in the dispersion for counterpropagating spin waves which reverses sign upon reversal of the direction of the externally applied magnetic field. From this asymmetry we deduce the strength of the interfacial DMI. Micromagnetic simulations confirm that the observed difference in the wave numbers and the signature of the asymmetry are characteristic for the occurrence of an interfacial DMI at the Pt/Co interface and cannot be explained by the uniaxial perpendicular magnetic anisotropy field originating from the same interface.

DOI： 10.1103/PhysRevB.92.220413

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the Néel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-orderd FeRh thin films by a magnetic field and electric current only, which open a realistic pathway towards operational antiferromagnetic memory devices.

DOI： 10.1063/1.4931567

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

Massless Dirac electron systems such as graphene exhibit a distinct half-integer quantum Hall effect, and in the bipolar transport regime co-propagating edge states along the p-n junction are realized. Additionally, these edge states are uniformly mixed at the junction, which makes it a unique structure to partition electrons in these edge states. Although many experimental works have addressed this issue, the microscopic dynamics of electron partition in this peculiar structure remains unclear. Here we performed shot-noise measurements on the junction in the quantum Hall regime as well as at zero magnetic field. We found that, in sharp contrast with the zero-field case, the shot noise in the quantum Hall regime is finite in the bipolar regime, but is strongly suppressed in the unipolar regime. Our observation is consistent with the theoretical prediction and gives microscopic evidence that the edge states are uniquely mixed along the p-n junction.

DOI： 10.1038/ncomms9066

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Magnetic domain wall (DW) motion induced by nanosecond current pulses is investigated in Co/Ni nanowires where the DW motion is driven by either adiabatic spin transfer torque (STT) or spin Hall torque (SHT). The DW displacement, including transient displacement and steady-state displacement, is found to be linearly related to the current pulse duration for both current-induced torques. The transient displacement is found to be less than 10% of the DW displacement. This result implies that the DW position can be controlled by tuning the duration of the current pulse, which enables a robust operation of racetrack memory.

DOI： 10.7567/APEX.8.073008

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We show that our ferromagnetic resonance (FMR) measurement based on the rectification effect is sufficiently sensitive for characterizing various static and dynamic magnetic properties of a sub-nanometer ferromagnetic film where the interfacial effects dominate. The extracted properties, such as the Landg-factor, the effective demagnetizing field, and the Gilbert damping parameter, are reasonably well scaled with the film thickness, indicating that our measurements clearly capture the interfacial properties of the sub-nanometer-thick film. In particular, the capability of the g-factor extraction in the ultrathin film will be very helpful for characterizing the various interfacial effects involved with interfacial orbit moments and spin-orbit interactions.

DOI： 10.7567/APEX.8.073003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We studied the magnetic domain wall (DW) creep motion in two driving forces: external magnetic field and spin Hall torque (SHT). The dimensional crossover from two to one dimension is identified by looking at the distribution width of the DW velocity depending on the wire width. The distribution widths are found to be similar regardless of the driving forces in narrow wires, whereas they show nonnegligible differences depending on the driving force in wide wires. Therefore, the dimensional crossover implies that the effective magnetic field induced by the SHT becomes equivalent to the external magnetic field only when the wire is considered as one-dimensional.

DOI： 10.7567/APEX.8.073004

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

We develop a theory for spin transported by coherent Néel dynamics through an antiferromagnetic insulator coupled to a ferromagnetic insulator on one side and a current-carrying normal metal with strong spin-orbit coupling on the other. The ferromagnet is considered within the monodomain limit and we assume its coupling to the local antiferromagnet Néel order at the ferromagnet|antiferromagnet interface through exchange coupling. Coupling between the charge current and the local Néel order at the other interface is described using spin Hall phenomenology. Spin transport through the antiferromagnet, assumed to possess an easy-axis magnetic anisotropy, is solved within the adiabatic approximation and the effect of spin current flowing into the ferromagnet on its resonance linewidth is evaluated. Onsager reciprocity is used to evaluate the inverse spin Hall voltage generated across the metal by a dynamic ferromagnet as a function the antiferromagnet thickness.

DOI： 10.1103/PhysRevB.92.020409

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Field-driven magnetic domain wall (DW) motion was investigated in ferrimagnetic GdFeCo wires with perpendicular magnetic anisotropy. The DW velocity as a function of the out-of-plane magnetic field exhibited the Walker breakdown phenomenon. The DW velocity was found to be significantly affected by the in-plane bias field: a minimum DW velocity was observed at a finite in-plane magnetic field (Hm), and the sign of Hm was found to reverse when the DW structure was changed from up-down-to down-up. These results imply that chiral DWs are formed in ferrimagnetic GdFeCo wires, despite their bulk and amorphous phase.

DOI： 10.7567/APEX.8.073001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

We investigated the antiferromagnetic-ferromagnetic phase transition of FeRh nanowires induced by an electric current. The critical current Icr for the phase transition decreases with increasing the sample temperature. It is found that the RcrI2cr, where Rcr is the resistance at Icr, linearly decreases as the sample temperature increases, suggesting that the temperature raised by the Joule heating is responsible for the transition. We also studied for various wire widths to characterize the heat dissipation of the nanowires. Our results provide a way to explore the Joule heating in high density nanosized electrical devices where significant electric current flow is involved.

DOI： 10.7567/JJAP.54.073002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scientific Reports  

Parity effect, which means that even-odd property of an integer physical parameter results in an essential difference, ubiquitously appears and enables us to grasp its physical essence as the microscopic mechanism is less significant in coarse graining. Here we report a new parity effect of quantum Hall edge transport in graphene antidot devices with pn junctions (PNJs). We found and experimentally verified that the bipolar quantum Hall edge transport is drastically affected by the parity of the number of PNJs. This parity effect is universal in bipolar quantum Hall edge transport of not only graphene but also massless Dirac electron systems. These results offer a promising way to design electron interferometers in graphene.

DOI： 10.1038/srep11723

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

We have developed a novel ferromagnetic resonance (FMR) measurement technique using the magneto-optical Kerr effect. The measurement technique uses microwave-frequency, intensity-modulated light to stroboscopically measure the Kerr angle due to the magnetization precession. We demonstrate that this stroboscopic magneto-optical Kerr effect provides a frequency domain and phase sensitive FMR measurement. The measurement is sensitive enough to detect the precessing magnetization with the precession cone angle below 1°.

DOI： 10.1063/1.4922126

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

We employed micro-focused Brillouin light scattering to study the amplification of the thermal spin wave eigenmodes by means of a pure spin current, generated by the spin-Hall effect, in a transversely magnetized Pt(4 nm)/NiFe(4 nm)/SiO2(5 nm) layered nanowire with lateral dimensions 500 × 2750 nm2. The frequency and the cross section of both the center (fundamental) and the edge spin wave modes have been measured as a function of the intensity of the injected dc electric current. The frequency of both modes exhibits a clear redshift while their cross section is greatly enhanced on increasing the intensity of the injected dc. A threshold-like behavior is observed for a value of the injected dc of 2.8 mA. Interestingly, an additional mode, localized in the central part of the nanowire, appears at higher frequency on increasing the intensity of the injected dc above the threshold value. Micromagnetic simulations were used to quantitatively reproduce the experimental results and to investigate the complex non-linear dynamics induced by the spin-Hall effect, including the modification of the spatial profile of the spin wave modes and the appearance of the extra mode above the threshold.

DOI： 10.1063/1.4907612

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

We report the relation between current induced effective fields and ferromagnetic layer thickness. Hall measurements with rotating magnetic field show that the transverse and perpendicular effective fields have linear relations to the inverse of the magnetic moment m per area S. The results imply that both of these effective fields may originate from spin angular momentum transferring. However, the non-zero intercept of the transverse field at m/S = 0 implies that magnetization independent effects, such as Rashba effect, may contribute to transverse field.

DOI： 10.1063/1.4914897

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We prepare the high quality epitaxial MgO(001)[100]/Pt(001)[100]/NiO(001)[100]/FeNi/SiO2 films to investigate the spin transport in the NiO antiferromagnetic insulator. The ferromagnetic resonance measurements of the FeNi under a spin current injection from the Pt by the spin Hall effect revealed the change of the ferromagnetic resonance linewidth depending on the amount of the spin current injection. The results can be interpreted that there is an angular momentum transfer through the NiO. A high efficient angular momentum transfer we observed in the epitaxial NiO can be attributed to the well-defined orientation of the antiferromagnetic moments and the spin quantization axis of the injected spin current.

DOI： 10.1063/1.4918990

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

We have investigated the temperature dependence of current-induced magnetic domain wall (DW) motion in a Co/Ni nanowire, where the spin Hall torque is responsible for the DW motion. The threshold current density (Jth) for DW motion is found to be dependent on the temperature T and the depinning magnetic field Hdep, which is different from the symmetric Co/Ni system where Jth is insensitive to T and Hdep. This result indicates that an extrinsic pinning governs the DW motion when it is driven by the spin Hall torque. Our work therefore suggests that reducing the extrinsic pinning is a key for achieving a low-power-consumption device.

DOI： 10.7567/JJAP.54.038004

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We present evidence of a localized magnetic domain-wall (DW) oscillator in Co/Ni nanowires. It is found that a DW is localized by the simultaneous application of a high magnetic field larger than the depinning field and a dc current smaller than the threshold current. A one-dimensional model and micromagnetic simulation reveal that the localized DW is in a precessional mode. Our results suggest that a localized magnetic DW oscillator can be realized by appropriately adjusting the magnetic field and dc current.

DOI： 10.7567/APEX.8.023003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

We investigate the in-plane field dependence of current-induced magnetic domain wall motion in asymmetric Co/Ni nanowires. The application of an in-plane field changed the direction of domain wall motion. In a systematic study, by varying the magnetic layer thickness, we show that the in-plane field induces a crossover from spin Hall torque to adiabatic spin-transfer torque for the magnetic domain wall motion. Furthermore, the dependence of the threshold current density on the in-plane longitudinal field provides a way for determining the strength of the Dzyaloshinskii-Moriya interaction.

DOI： 10.1103/PhysRevB.91.060405

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Scientific Reports  

DOI： 10.1038/SREP12591

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記述言語：日本語   出版者・発行元：The Magnetics Society of Japan  

We have shown by micromagnetic simulation that the wavelength of the spin wave (SW) is modulated when the SW propagates across a step between two ferromagnetic films with different thicknesses. Since the wavelength of the SW depends on the film thickness, the thickness difference works as the different medium in Snell's law. The wavelength modulation obtained by the simulation showed a good agreement with Snell's law.

DOI： 10.3379/msjmag.1506R004

CiNii Books

その他リンク： https://jlc.jst.go.jp/DN/JLC/20012933769?from=CiNii

掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/S00540-015-1991-2

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掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

We show that the magnitude of the Dzyaloshinsky-Moriya interaction (DMI) can be determined by a field-driven domain-walls (DWs) annihilation measurement. It is predicted that the DMI induces antiparallel Néel DWs which form a metastable 360° DW when they approach to each other. We find that an annihilation field, over which two DWs collide and vanish, is proportional to the magnitude of the DMI. This result suggests that the DMI can be quantified by a simple measurement of the annihilation field.

DOI： 10.7567/JJAP.53.108001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We investigate the magnetization dynamics in synthetic antiferromagnetic (SyAFM) Fe/[Co/Cu]10/Co/Pt multilayers using the microwave rectifying effect. We observe two distinct resonant modes in the dynamics. Numerical simulations reveal that the resonant modes can be attributed to acoustic and optical modes, which are the characteristic resonant modes of antiferromagnetically coupled materials. It is found that the linewidth of the optical mode is larger than that of the acoustic mode by a factor of 5. This broadening of the linewidth in the optical modes can be explained by the mutual spin pumping effect between the magnetizations precessing out of phase. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.7.063010

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We report a systematic study of the DW motion in perpendicularly magnetized Co/Ni nanowires having different thicknesses with structure inversion asymmetry. The transition from bulk to interfacial effects is confirmed as a change in the DW motion direction at a reduced layer thickness. The bias field dependence reveals that the adiabatic spin transfer torque (STT) dominates the DW motion in the thick regime, whereas the interfacial torque originating from the spin Hall effect (SHE) is responsible for the DW motion with a fixed DW chirality induced by the Dzyaloshinskii-Moriya interaction (DMI) in the thin regime. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.7.053006

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We investigate the wire-width dependence of the critical current density for the motion of a magnetic domain wall (DW) in asymmetric Co/Ni nanowires, where spin Hall torque dominates the current-induced DW motion. It is found that both the critical current density for DW motion and the pinning field of a DW increase as the wire width decreases and that the critical current density for DW motion is proportional to the pinning field of the DW; this finding suggests a tradeoff between low-power operation and thermal stability in magnetic domain-wall-motion devices driven by spin Hall torque. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.7.053003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We report the real-time observation of spin-wave propagation across a step inserted between two ferromagnetic films with different thicknesses. Because the dispersion relation of the spin wave depends on the thickness of the film, the step works as a junction to affect the spin wave propagation. When the spin wave transmits through the junction, the wavenumber undergoes modulation as per Snell's law, which states that the refraction index is proportional to the wavenumber. From the viewpoint of magnonics, the present achievement opens up new possibilities of controlling the wavenumber of spin waves. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.7.053001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Magnetic domain wall (DW) creep motions driven by a magnetic field and by the spin Hall (SH) torque are investigated in perpendicularly magnetized Co/Ni nanowires with structural inversion asymmetry. It is found that the DW arrival time distribution becomes wider when a DW is driven by the SH torque compared with that driven by a magnetic field. Our results indicate that the SH torque and a magnetic field drive a DW in different ways in the DW creep regime, although the SH torque is generally considered to induce an effective field. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.7.053005

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Spin-wave (SW)-induced domain wall (DW) motion is investigated in a perpendicularly magnetized system by micromagnetic simulation. We particularly assume simulation parameters for Co/Ni nanowires widely used in the experiment for spin-torque-driven DW motion. It is found that the domain wall moves toward the SW source in a broad frequency range, while it resonantly moves away from the SW source at certain frequencies. Our results indicate that the direction of the DW motion can be controlled by tuning the SW excitation frequency. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.7.033001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

Two important mechanisms for current-induced domain wall (DW) dynamics, namely, precessional DW motion driven by the adiabatic spin transfer torque and steady DW motion induced by the spin Hall torque, have been proposed and experimentally confirmed. However, the effect of the spin Hall torque on precessional DW motion has not been reported yet. Here, we show that the spin Hall torque affects the precessional DW motion when the in-plane field is applied. It is found that the in-plane field induces a half rotation time difference during DW precession, which gives rise to the nonvanishing spin Hall torque on the precessional DW motion. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.7.033005

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

We have been investigating the spin motive force induced by magnetization dynamics in ferromagnetic materials. Ferrimagnetic materials are expected to exhibit even larger spin motive force due to their spatially staggered magnetic structure and high frequency spin wave modes. We believe that magnetite (Fe 3O4) is one of the candidates for this purpose. Here, we report magnetic resonance in Fe3O4 thin films epitaxially grown on a MgO (001) substrate. The gyromagnetic ratio and the effective saturation magnetization are estimated to be 1.71 × 1011 s -1T-1 and 364 emu/cm3, respectively. The Gilbert damping constant of 0.02 is obtained from the magnetic field dependence of the linewidth. We expect to investigate the spin motive force induced from this magnetic resonance. © 2013 IEEE.

DOI： 10.1109/TMAG.2013.2274270

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We show that the angle-dependent Hall measurement is an effective method to determine the current-induced effective fields by investigating MgO/Fe/Ta and MgO/Fe/Pt/Ta multilayer structures. The experimentally obtained Hall resistance under a relatively large dc electrical current is well described by considering two components of current-induced effective fields, which may be related to the spin Hall effect and the Rashba effect. The directions of the effective fields are consistent with and their magnitudes are comparable to those reported previously for similar multilayer structures. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.113002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

This paper predicts the possibility to achieve synchronization (via injection locking to a microwave current) of spin-transfer torque oscillators based on hybrid spin-valves composed by two free layers and two perpendicular polarizers at zero bias field. The locking regions are attained for microwave frequency near 0.5f0, f0, and 2f0, where f 0 is the input oscillator frequency. Those properties make this system promising for applications, such as high-speed frequency dividers and multipliers, and phase-locked-loop demodulators. © 2013 American Institute of Physics.

DOI： 10.1063/1.4795597

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

The authors have investigated the current-induced magnetic domain wall (DW) motion in perpendicularly magnetized Co/Ni nanowire with structural inversion asymmetry (SIA). In this system, DW motion to the direction of electric current flow, not electron flow, and high DW velocity up to 110 m/s were confirmed, which have never been observed in Co/Ni systems without SIA. In addition, we found that the DW velocity showed a strong dependence on the perpendicular magnetic field in the range of ±100 Oe. These results suggest that DW in the Co/Ni nanowire with SIA moves in the steady mode, not in the precessional mode. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.033001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Express  

We present the results of a perpendicular magnetic tunnel junction (MTJ) that displays simultaneously low critical switching current and voltage, as well as high thermal stability factor. These results were achieved using a free layer of the MgO/CoFeB/MgO structure by increasing the spin torque efficiency to an average of 3.0 k BT/μA for 37-nm-diameter junctions, about three times that of a MgO/CoFeB/Ta free layer, which makes it the highest value reported to date. By comparing two films with different RA, hence different switching voltage and power, we explore the contributions of heating and voltage-modulated anisotropy change to the switching properties. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.5.093008

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

We report measurements of spin-torque-driven oscillations in magnetic multilayer devices containing two in-plane-oriented free layers designed to have significant coupling between them. They are driven to oscillate by spin-transfer torque from two perpendicularly oriented polarizers. For both measured devices and micromagnetic simulations, we find that the oscillations in the two free layers are phase locked, resulting in a frequency doubling and large output signals. The simulations suggest that the oscillations are due to spatially nonuniform dynamics characterized by coupled large-amplitude motion of the two free layers. © 2012 American Physical Society.

DOI： 10.1103/PhysRevB.86.060411

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences  

We discuss recent highlights from research at Cornell University, Ithaca, New York, regarding the use of spin-transfer torques to control magnetic moments in nanoscale ferromagnetic devices. We highlight progress on reducing the critical currents necessary to produce spin-torque-driven magnetic switching, quantitative measurements of the magnitude and direction of the spin torque in magnetic tunnel junctions, and single-shot measurements of the magnetic dynamics generated during thermally assisted spin-torque switching. © 2011 The Royal Society.

DOI： 10.1098/rsta.2011.0169

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

An inductive-based detection method of ferromagnetic resonance spectrum is demonstrated. For a single microscopic (∼40 nm × 40 μm} magnetic dot, which is much smaller than the microwave wavelength, the change in the microwave transmission signal is as large as 15 dB when its magnetic permeability changes. This detection is several orders more sensitive than the conventional transmission line method. Further understanding and development of this concept may lead to a microscopic microwave permeability sensor. © 2006 IEEE.

DOI： 10.1109/TMAG.2010.2087376

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance dynamics. The Oersted field from the current also generates a ferromagnetic resonance signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle. © 2011 American Physical Society.

DOI： 10.1103/PhysRevLett.106.036601

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1053/J.JVCA.2010.03.013

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We have fabricated MgO-barrier magnetic tunnel junctions with a Co/Ni switching layer to reduce the demagnetizing field via interface anisotropy. With a fcc-(111) oriented Co/Ni multilayer combined with an FeCoB insertion layer, the demagnetizing field is 2 kOe and the tunnel magnetoresistance can be as high as 106%. Room-temperature measurements of spin-torque switching are in good agreement with predictions for a reduced critical current associated with the small demagnetization for antiparallel-to-parallel switching. For parallel-to-antiparallel switching the small demagnetization field causes spatially nonuniform reversal nucleated at the sample ends, with a low energy barrier but a higher switching current. © 2010 American Institute of Physics.

DOI： 10.1063/1.3481798

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

In the first part of this paper, we report a systematic study on the structural evolution under rapid thermal annealing and the corresponding transport properties in magnetic tunnel junctions (MTJs) with a crystalline MgO barrier. The results clearly indicate that high tunneling magnetic resistance can be achieved by annealing MTJs at avery short time, and it is directly related to the formation of (001) crystalline structures. In the second part, we report the spin dynamics in tunneling structure through direct electrical detection. A surprisingly large voltage generation in F/I/N and F/I/Fjunctions was observed, which is contradictory to the prediction from the standard spin-pumping theory. We proposed a theoretical formalism to study spin-pumping effects in ferromagnetic multilayer structures. The formalism can yield a remarkably cleanphysical picture of the spin and charge pumping in tunneling structures. The calculated values are consistent with experimental results. © 2009 IEEE.

DOI： 10.1109/TMAG.2009.2024126

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We investigated the tunneling magnetoresistance change in magnetic tunnel junctions in the presence of external microwaves. The changing relative angle between the free layer and the pinned layer results in a rectification of the average resistance change. Due to its miniature size and its sensitivity to the microwave magnetic field, the magnetic tunnel junction could be utilized as a microwave power sensor with the ability to detect microwave frequencies. Studying microwave power and bias current dependencies reveals desired sensor features with linear responses and enhanced signal levels. © 2009 American Institute of Physics.

DOI： 10.1063/1.3231874

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

We have developed an experimental technique to electrically characterize ferromagnetic resonance (FMR) with a large precession cone angle by using magnetic tunnel junctions on a coplanar waveguide. We observed FMR of a Ni 80Fe20 layer as the tunneling resistance change capturing the angle between the Ni80Fe20 precession magnetization and a fixed magnetization in a reference electrode. The resonant frequency shifts with increasing microwave power as a result of the large precession cone angle that reduces the effective anisotropy field. We confirmed the validity of our results by the numerical simulations based on the Landau-Lifshitz-Gilbert equation. © 2009 IEEE.

DOI： 10.1109/TMAG.2008.2002572

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

In this study, the effective spin-mixing conductance in Ni80 Fe20 /Pt was investigated by measuring the interface-induced enhancement of the Gilbert damping constant. Ferromagnetic resonance spectra were measured in coplanar waveguide geometry with different incident microwave powers. The nonlinear behavior of normal Gilbert damping G0 and effective spin-mixing conductance g have been observed when the incident microwave power is above a critical ac field hrf of 1.6 Oe. Both phenomena are explained by considering the coupling between spin coherent precession and spin wave modes. This work demonstrates the nonlinear behavior of the effective spin-mixing conductance g. It suggests that the nonlinear spin wave modes excited at high incident microwave power are detrimental to the spin pumping effect and should be avoided in future spin battery designs. The capability of tuning G0 and g through the microwave power is also useful for the fundamental study on the damping mechanism. © 2009 American Institute of Physics.

DOI： 10.1063/1.3072443

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DOI： 10.1016/j.neulet.2009.01.048

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We significantly reduce the critical current Ic0 for the onset of spin torque switching of the free layer in nanometer-scale in-plane magnetized spin valves by partially cancelling its intrinsic demagnetization field through the utilization of Co/Ni multilayer free layers. The out-of-plane magnetic anisotropy arising from the Co/Ni interfaces reduces the effective demagnetization field (Heff) while not significantly affecting the thermal stability of the free layer. A zero-thermal-fluctuation critical current density Jc0 ∼2× 106 A/ cm2 is determined through both current ramp rate and nanosecond pulse measurements, and comparisons with large Heff control samples confirm that this strategy is efficient in substantially decreasing Ic0. © 2009 American Institute of Physics.

DOI： 10.1063/1.3107262

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Dianzi Keji Daxue Xuebao/Journal of the University of Electronic Science and Technology of China  

The spintronics refers to the research area where electron spins, in additional to or sometimes in place of electron charges, are controlled and manipulated to give rise to an array of properties. Spintronic devices have already found applications in computer hard drive and magnetic random access memory, profoundly changed the information technology industry. These applications utilize the spin polarized transport where electron with fixed spin direction transverse through magnetic heterostructures. More recently, investigation of spin dynamics in spintronic device relates microwave with spin polarized transport, offering significant potential for novel microwave devices with dimension far less than the microwave wavelength. In this "review-like" article, we first briefly introduce the concept of spintronic devices. Microwave experiments with spintronic devices are discussed next in the context of microwave assisted switching and spin pumping phenomenon. The former has potential for developing high density computer hard disk, the latter, with the development of direct electronic detection, could lead to miniaturized and passive microwave detector.

DOI： 10.3969/j.issn.1001-0548.2009.05.004

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

We theoretically study the recently observed tunnel-barrier-enhanced dc voltage signals generated by magnetization precession in magnetic tunnel junctions. While the spin pumping is suppressed by the high tunneling impedance, two complementary processes are predicted to result in a sizable voltage generation in ferromagnet (F)|insulator (I)|normal metal (N) and F |I| F junctions with one ferromagnet being resonantly excited. Magnetic dynamics in F |I| F systems induce a robust charge pumping, translating into voltage in open circuits. In addition, dynamics in a single ferromagnetic layer develop longitudinal spin accumulation inside the ferromagnet. A tunnel barrier then acts as a nonintrusive probe that converts the spin accumulation into a measurable voltage. Neither of the proposed mechanisms suffers from spin relaxation, which is typically fast on the scale of the exponentially slow tunneling rates. The longitudinal spin-accumulation buildup, however, is very sensitive to the phenomenological ingredients of the spin-relaxation picture. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.78.020401

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We report the study of the real-time evolution of tunneling magnetoresistance (TMR) in CoFeBMgOCoFeB junctions during annealing at 380 °C. The TMR quickly developed at the early stage of the annealing, with 200% magnetoresistance observed in less than 10 min, followed by a slow approach to saturation. This evolution of TMR was correlated with the structural changes, including crystallization of amorphous CoFeB electrodes and improvement of barrier quality during the annealing. © 2008 American Institute of Physics.

DOI： 10.1063/1.2903147

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

Microwave assisted magnetization switching was investigated using Fe30 Co70 Al2 O3 Ni80 Fe20 magnetic tunnel junctions incorporated with a coplanar waveguide. Coercivity reduction (or switching field) of Ni80 Fe20 layer was reduced with a microwave excitation. It was found that the coercivity reduction depends on both frequency and power of the microwave. The numerical simulation based on the Landau-Lifshitz-Gilbert equation reproduced the trend of the experimental data. The results indicate that microwave can be an efficient mean to switch the magnetization of a thin film. © 2008 American Institute of Physics.

DOI： 10.1063/1.2838290

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

Chromium doped zinc telluride thin films with various doping concentrations are fabricated by magnetron sputtering. These films are ferromagnetic and the Curie temperature increases with Cr concentration. X-ray diffraction, transmission electron microscopy, and magnetic circular dichroism characterizations show that the films are free of Cr1-x Tex impurities and the ferromagnetism is intrinsic. The transport study shows that the resistivity and magnetoresistance are governed by variable range hopping at low temperatures. A negative magnetoresistance as large as -57% is observed at 5 K. The magnetoresistance and its temperature dependence can be well explained by a model involving an increase in the localization length of carriers with a magnetic field in the hopping region. An anomalous Hall effect is also observed and a possible origin of the sign difference between the anomalous Hall resistance and ordinary Hall resistance is discussed. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.77.155207

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

We report the electrical detection of magnetization dynamics in an Al/AlOx/Ni80Fe20/Cu tunnel junction, where a Ni80Fe20 ferromagnetic layer is brought into precession under ferromagnetic resonance conditions. The dc voltage generated across the junction by the precessing ferromagnet is enhanced about an order of magnitude compared to the voltage signal observed when the contacts in this type of multilayered structure are Ohmic. We discuss the relation of this phenomenon to magnetic spin pumping and speculate on other possible underlying mechanisms responsible for the enhanced electrical signal. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevLett.100.067602

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/S00540-008-0651-1

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Microwave-assisted magnetization switching was investigated using Fe 30Co70/AlOx/Ni80Fe20 magnetic tunnel junctions incorporated with a coplanar waveguide. Coercivity field of Ni80Fe20 layer was dramatically reduced in a small amplitude microwave. The authors eliminated the thermal effect in coercivity reduction by comparing two types of measurements which are with and without spin precession in the presence of microwave. It was found that the coercivity reduction depends on both frequency and power of the microwave. The numerical simulation based on Landau-Lifshitz-Gilbert equation reproduced the trend of the experimental data. The results indicate that microwave can be an efficient means to switch the magnetization of a thin film. © 2007 American Institute of Physics.

DOI： 10.1063/1.2720746

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

Off-axis electron holography was used to investigate the barrier profile of the Py Al Ox Zr Oy Py magnetic tunnel junctions with different Zr Oy thicknesses. The tunneling magnetoresistance (TMR) has a strong dependence on bias voltage and the bias voltage for maximum TMR is shifted from zero. This shift increases with Zr Oy barrier thickness due to the increasing barrier asymmetry in the junctions. The evolution of barrier asymmetry was directly observed by the phase change of the off-axis electron holography, which unambiguously shows the barrier profile changes from triangular to trapezoidal shape as increasing of Zr Oy thickness. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevB.75.134420

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

Magnetic nanoparticles coated with a biocompatible polymer are potential candidates for biomedical applications associated with the detection and treatment of cancer. By varying the length of a reaction tube, the nanoparticle size increases from 10 to 30 nm with a 1-3 nm carboxyl terminated polyethylene glycol (cPEG) coating. The saturation magnetization for all samples is greater than 100 emu/g. By increasing the length of the reaction tube there is an incorporation of an amorphous phase. Subjecting samples to a 4 Oe magnetic field oscillating at 500 kHz there are two characteristic temperatures depending on particle size. The temperature measured for larger particles saturates with time to 35 °C. Below a critical nanoparticle size the temperature reached exceeds 50 °C within the same timeframe. © 2006 IEEE.

DOI： 10.1109/TMAG.2006.879075

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Magnetic tunneling junctions (MTJs) with MgO tunnel barrier have been fabricated on both oriented and nonoriented buffer layers on Si(001) substrate by magnetron sputtering. FeCoMgOFeCo MTJs fabricated on oriented buffer layers show larger tunneling magnetoresistance (TMR) value up to 84% without high temperature postannealing, whereas those MTJs on nonoriented buffer layers show 45% of TMR. The high-resolution transmission electron microscopy images reveal an excellent morphology and very coherent crystal structure with FeCo (001) [110] MgO (001) [100] FeCo (001) [110] orientation. The results indicate that high TMR can be achieved without high temperature postannealing by sputtering deposition on appropriate oriented buffer layers. © 2006 American Institute of Physics.

DOI： 10.1063/1.2207835

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Tunnel magnetoresistance (TMR) of 21% is observed at low temperature in hybrid magnetic tunnel junctions (MTJs) composed of a magnetic semiconductor (Zn,Cr)Te and Co electrodes separated by an alumina barrier. The TMR is observed up to 250 K, which is a considerable improvement over previous work on MTJs with semiconductor electrodes. The temperature and bias dependence of the TMR are consistent with a transport model involving spin-polarized tunneling and spin-independent hopping through impurity states. © 2006 American Institute of Physics.

DOI： 10.1063/1.2205177

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

The magnetotransport properties and the structure of the magnetic tunnel junctions (MTJ) with L1 0-ordered FePt alloy electrodes were investigated. The MTJs were synthesized on the MgO(110) single crystal substrates. The structural characteristics of the MTJs were analyzed using x-ray diffraction, reflection high-energy electron diffraction and atomic force microscopy. The tunnel magnetoresistance (TMR) of MTJs was found to be 34% at 77 K with FePt alloy electrodes in which the degree of chemical order, S, was estimated to be ∼ to be 0.7. It was observed that the TMR of the MTJs with FePt alloy electrodes was increased with S, suggesting the spin polarization of L1 0-FePt alloys was enhanced by chemical ordering.

DOI： 10.1063/1.1669212

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

The preparation of epitaxial magnetic tunnel junctions (MTJ) on MgO(100) single crystal substrates with the help of plasma oxidation was discussed. Reflection high-energy electron diffraction (RHEED) was used to study the epitaxial relationship in the junctions. The significance of plasma oxidation in fabricating epitaxial magnetic tunnel junctions was also discussed.

DOI： 10.1063/1.1557338

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

Fe/MgF 2/Co magnetic tunnel junctions (MTJs) with an oxide seed layer (MgO, Fe-O) inserted between an Fe bottom electrode and a MgF 2 barrier layer have been prepared through the use of molecular beam epitaxy, and the effects of the seed layers on structure of subsequently deposited MgF 2 barrier layers and tunnel magnetoresistance (TMR) have been investigated. The crystallographic orientation of MgF 2 layers depends significantly on the seed layers, and furthermore, it has been found that the surface roughness of MgF 2 layer is reduced by inserting a MgO seed layer. In Fe/MgF 2 (3-12 nm)/Co MTJs without any seed layer, top Fe and bottom Co electrodes contact each other through pin holes in MgF 2 layers. On the other hand, however, Fe and Co electrodes are separated both magnetically and electrically in Fe/MgO(0.3-0.5nm)/MgF 2 (2-5 nm)/Co MTJs, i.e., MgF 2-based MTJs have successfully been prepared by inserting a thin MgO seed layer, resulting in TMR of about 10% observed at 4.2 K. © 2002 American Institute of Physics.

DOI： 10.1063/1.1452200

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記述言語：英語   出版者・発行元：The Magnetics Society of Japan  

Ferromagnetic tunnel junctions (MTJs) in which a thin MgO seed layer was inserted between Fe bottom electrode and MgF₂ insulating barrier were fabricated through the use of molecular beam epitaxy. The structure and tunnel magnetoresistance (TMR) were investigated for Fe (200Å)/MgO (5Å)/MgF₂ (20Å)/Co (200Å) junctions. RHEED observation suggested that an MgF₂ layer deposited at room temperature was in amorphous or nanocrystalline state. The TMR ratio observed for a typical MTJ with barrier height of 1.6 eV was 1.8 % at 4.2 K and decreased with increasing temperature, down to 0.7 % at 293 K. It was found that the bias dependence of TMR shows a strong asymmetric feature, in contrast to conventional MTJs with amorphous alumina barriers.

DOI： 10.3379/jmsjmag.26.405

記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）  

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>グラフェンは、その簡易な単離方法と内在する豊富な物理のため、発見以来活発に研究がつづけられている。グラフェンでは二重ゲート構造でpn接合が容易に形成でき、量子ホール状態におけるpn接合での輸送特性が研究されてきた。我々は、この量子ホール状態でのpn接合で起きる電子の分配過程に着目し、この過程の動的特性理解のために、雑音測定を行った。その結果pn接合での分配過程に起因するショット雑音の観測に成功した。加えて、雑音強度を示すファノ因子も理論と一致することがわかった。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_1218

記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）  

開催年月日： 2022年9月

記述言語：日本語   会議種別：口頭発表（招待・特別）  

開催年月日： 2022年9月

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催年月日： 2022年8月

記述言語：日本語   会議種別：口頭発表（招待・特別）  

開催年月日： 2022年7月

記述言語：英語   会議種別：口頭発表（一般）  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2018年3月

記述言語：日本語  

開催年月日： 2017年

記述言語：日本語  

フェリ磁性体GdFeCoは、磁性を担う原子の角運動量の和が0となる角運動量補償温度(T_A_)を持つ物質として知られている。T_A_においては磁気回転比(γ_eff_)が発散することが理論的に知られており、電流駆動磁壁移動速度(v_DW_ ∝ γ_eff_)もT_A_で発散すると期待される。そこで今回我々は、フェリ磁性体GdFeCo/Ptにおいて電流駆動磁壁移動速度の温度依存性を測定し、T_A_近傍における振る舞いについて調査したのでその結果を発表する。

開催年月日： 2017年

記述言語：日本語  

磁性薄膜中で磁壁は欠陥のもつピニングポテンシャルによりピン留めされる。その際、磁壁はピニングポテンシャル内において周期tau_0で振動する。磁壁の滞在時間はtau_0とピニングポテンシャルの大きさによって決まる。これまでピニングポテンシャルの大きさについては数多く実験的に観測されてきたが、実験的にtau_0を求めた報告例は未だない。本研究ではCo/Ni細線において高周波電流を印加し、磁壁の共鳴からtau_0を求める試みに取り組んだので、その結果を報告する。

開催年月日： 2017年

記述言語：日本語  

フェリ磁性体は、二種類の磁化成分が互いに反平行に整列し、その総和を磁化として発現する物質である。また磁区と磁区の境界である磁壁に抵抗(磁壁抵抗)が発現することはこれまでに数多く報告されているが、フェリ磁性体における報告例は少ない。今回我々は垂直磁化膜であるフェリ磁性体GdFeCoにおいて磁壁抵抗を観測することに成功した。当日は磁壁抵抗が発現する機構について報告する予定である。

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

<p>近年反強磁性体スピントロニクスの研究は盛んに行われている。我々は反強磁性体の磁化を、強磁性体との交換結合を介して外部磁場で制御した。そのうえで電気的測定を用い、反強磁性体の磁気抵抗効果の観測を試みた。今回、我々は反強磁性体の磁化の回転に起因すると思われる抵抗の変化を観測したため、その結果を報告する。</p>

開催年月日： 2016年

記述言語：日本語  

<p>フェリ磁性体は、正味の磁化が0となる磁化補償温度(T_M_)を持つ物質として長年注目を集めてきた。しかしながら、フェリ磁性体の磁気抵抗効果、特に磁性体/非磁性金属の二層膜で発現するスピンホール磁気抵抗効果については、ほとんど研究されてこなかった。我々は、フェリ磁性体GdFeCo/Ptにおいて異常ホール効果・異方性磁気抵抗効果・スピンホール磁気抵抗効果の温度依存性を測定した。本講演では、これらの磁気抵抗効果の温度依存機構について発表する予定である。</p>

開催年月日： 2016年

記述言語：日本語  

<p>グラフェンは、その簡易な単離方法と内在する豊富な物理のため、発見以来活発に研究がつづけられている。グラフェンでは二重ゲート構造でpn接合が容易に形成でき、量子ホール状態におけるpn接合での輸送特性が研究されてきた。我々は、この量子ホール状態でのpn接合で起きる電子の分配過程に着目し、この過程の動的特性理解のために、雑音測定を行った。その結果pn接合での分配過程に起因するショット雑音の観測に成功した。加えて、雑音強度を示すファノ因子も理論と一致することがわかった。</p>

開催年月日： 2016年

記述言語：日本語  

<p>我々はゲート電極／絶縁体／磁性体という構造において磁性体中の電子密度を変調して磁性を制御する電界効果の研究を行ってきた。磁性体が多磁区状態にあるとき、その磁区幅は磁気異方性定数、飽和磁化、交換スティフネスを含む関数で表される。今回我々は電界による磁区幅、磁気異方性定数、飽和磁化の変化を同一試料にて測定し、交換スティフネスに対する電界効果を評価したため、その結果を報告する。</p>

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：日本語  

開催年月日： 2016年

記述言語：英語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2013年

記述言語：日本語  

開催年月日： 2003年3月

記述言語：日本語  

開催年月日： 2002年9月

記述言語：日本語  

開催年月日： 2002年8月

記述言語：日本語  

開催年月日： 2002年3月

記述言語：日本語  

記述言語：日本語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Honolulu; HI; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Kyoto; Japan  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Jeju; Korea  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：La Thuile; Italy  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：San Diego; CA; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Tsukuba; Ibaraki  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Dallas; TX; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Austin; TX; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Pittsburgh; PA; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Sacramento; CA; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Portland; OR; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Yorktown Heights; NY; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Atlanta; GA; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Scottsdale; AZ; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：San Diego; CA; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Baltimore; MD; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：金属材料研究所、仙台  

記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

記述言語：日本語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：東京理科大学、東京  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：東京農工大、東京  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：京都大学、宇治  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：梅田、大阪  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：中央大学、東京  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：立命館大学、京都  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：広島大学、広島  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：名古屋、愛知  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：御茶ノ水、東京  

記述言語：日本語   会議種別：口頭発表（招待・特別）  

記述言語：日本語   会議種別：口頭発表（招待・特別）  

記述言語：日本語   会議種別：口頭発表（招待・特別）  

記述言語：日本語   会議種別：口頭発表（招待・特別）  

記述言語：日本語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：中央大学、東京  

記述言語：英語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Kashiwa; Chiba; Japan  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Tohoku U.; Sendai; Japan  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：San Diego; CA; USA  

記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Messina; Italy  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Sendai; Japan  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Univ. of Tokyo; Tokyo  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：秋田大学、秋田  

記述言語：英語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

記述言語：英語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Baltimore ;MD; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Pittsburgh; PA; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：新潟市、新潟  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：神奈川大学、横浜  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Tampa; FL; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：New Orleans; LA; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：New Orleans; LA; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Tampa; FL; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：The Johns Hopkins University; Baltimore; MD; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Carnegie Mellon University; Pittsburgh; PA; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Washington; DC; USA  

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Los Angels. CA; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：New York; NY; USA  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Pittsburgh; PA; USA