Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Magnetic thin films showing high perpendicular magnetic anisotropy, K-u, and low saturation magnetization, M-s, are essential for realizing a small switching current in spintronic devices utilizing the current induced magnetization switching phenomena. The Cu2Sb-type MnAlGe intermetallic compound is a material showing uniaxial magnetocrystalline anisotropy with a relatively low M-s, which is attractive for spintronic application. In this study, the layer thickness dependence of K-u was investigated in poly-crystalline MnAlGe films, and the MgO template effect is discussed to achieve perpendicularly magnetized films in a few-nanometer thickness range. Experimental results suggested that the (001)-texture for the perpendicular magnetization was promoted by the MgO(001) template through the solid-phase epitaxy growth by annealing, which is similar with that in conventionally used CoFeB|MgO layered samples. K-u of about 2 x 10(6) erg/cm(3) was achieved in a 5 nm-thick MnAlGe film using MgO buffer and capping exhibiting a low M-s value of approximately 200 emu/cm(3) at room temperature. Although the magnitude of K-u is still in a moderate range, the low M-s is a promising feature for spintronic application.

DOI： 10.1063/9.0000138

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Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals  

Ferromagnetic MnAlC (¸-phase) can be synthesized by a single-route conventional reactive sintering method. The maximum magnetization and coercivity were 75.8 Am2/kg and 57 mT, respectively. The ¸-phase fraction was evaluated to be 81 mass% for Mn55Al45C2 annealed at 1273 K. The ¸-phase of Mn55Al45C2 can be synthesized at an annealing temperature from 873 to 1273 K, whereas that of Mn55Al45 cannot be synthesized. It was indicated that the phase stability of the hcp-phase (¾-phase) was improved by adding carbon, resulting in an ¾¸ transformation.

DOI： 10.2320/matertrans.mt-m2020166

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals  

Combined accelerating effects of epsilon-tau phase transformation by in-magnetic-field annealing and Zn-addition were investigated for Mn53Zn2Al45 in magnetic fields up to 15 T. The in-field annealing for Zn-added sample accelerated the epsilon-tau transformation 16 times faster than Mn53Zn2Al45 at annealing temperature of 623 K. The reduction of magnetization after finishing epsilon-tau transformation was also more rapid than that of Mn53Zn2Al45. However, magnetic-field-induced acceleration of epsilon-tau phase transformation and suppression of precipitation of beta-phase were observed for Zn-added alloy Mn53Zn2Al45 annealed at 573 K. The obtained results suggested that the beta-phase stabilized against both alpha- and epsilon-phases by Zn-addition. Therefore, although the epsilon-tau transformation was efficiently accelerated by in-field annealing of Mn53Zn2Al45, more precisely control of annealing time is required for obtaining high fraction of ferromagnetic tau-phase.

DOI： 10.2320/matertrans.mt-m2020235

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Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0012348

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DOI： 10.1063/5.0011875

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Language：English   Publisher：AMER INST PHYSICS  

DOI： 10.1063/5.0012962

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The anomalous Nernst effect (ANE) is investigated for 100nm Co-x(MgO)(1-x) granular films as a function of the Co volume fraction (x) changes. The results show that by slightly adding MgO into the Co matrix, the anomalous Nernst angle (theta(AN)) can be largely enhanced more than three times compared with that of pure Co, which also results in the obvious change in ANE voltage. The transverse conductivity sigma XYA sigma XX shows distinct linear behavior in three regimes, which indicates different anomalous Hall effect (AHE) mechanisms. By qualitative Mott-relation analysis, we found that the non-monotonic dependence of ANE on x is associated with the change in AHE mechanisms.

DOI： 10.1063/1.5140461

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Two-dimensional materials such as hexagonal boron nitride (h-BN) and graphene have attracted wide attention in nanoelectronics and spintronics. Since their electronic characteristics are strongly affected by the local atomic structure, the heteroatom doping could allow us to tailor the electronic and physical properties of two-dimensional materials. In this study, a non-chemical method of heteroatom doping into h-BN under high-energy ion irradiation was demonstrated for the LiF/h-BN/Cu heterostructure. Spectroscopic analysis of chemical states on the relevant atoms revealed that 6% +/- 2% fluorinated h-BN is obtained by the irradiation of 2.4 MeV Cu2+ ions with the fluence up to 1014 ions cm(-2). It was shown that the high-energy ion irradiation leads to a single-sided fluorination of h-BN by the formation of the fluorinated sp(3)-hybridized BN.

DOI： 10.1088/1361-6528/ab5bcc

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Cu2Sb-type intermetallic compound, MnAlGe, is known to exhibit uniaxial magnetocrystalline anisotropy and relatively small saturation magnetization, which is suitable for spintronic application, e.g. spin-transfer phenomena requiring small critical current density. Ge-concentration dependence of the crystal structures, saturation magnetization, M-s, and perpendicular magnetic anisotropy, K-u was investigated for MnAlGe films prepared onto silicon substrates with a thermally oxidized amorphous layer. For the stoichiometric and Ge-rich samples, the films exhibited (001)-texture with perpendicular magnetization. The maximum values of M-s and K-u were 270 emu/cm(3) and 4.8 x 106 erg/cm(3), respectively, which were comparable values with those reported for bulk and epitaxially grown films in literatures. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

DOI： 10.1063/1.5130388

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Language：Japanese  

DOI： 10.1080/14686996.2019.1633687

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DOI： 10.1063/1.5126324

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DOI： 10.7567/1882-0786/ab3e2d

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DOI： 10.1016/j.jallcom.2019.02.165

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DOI： 10.7567/1347-4065/aafe68

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DOI： 10.1063/1.5079982

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DOI： 10.1063/1.5087041

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Language：Japanese   Publishing type：Research paper (scientific journal)  

© 1965-2012 IEEE. In-magnetic-field annealing (IFA) effects on Zn-modified Mn-Al and Mn-Al-C were investigated at the annealing temperature of 573 K, which was around their $_Rftxt-{\mathrm {C } }$. Mn53Zn2Al45 showed the magnetic-field-induced acceleration of the phase transformation to $\text{L}1-{0}$ -phase ( $\tau $ -phase) and the suppression of that to nonferromagnetic equilibrium phase. For Mn55Al45C2, IFA effects were not clearly detected. These different magnetic field effects were discussed by the difference of the mechanism in stabilization of $\tau $ -phase. It is found by a thermal analysis that the modification of Zn stabilized $\tau $ -phase against $\epsilon $ -phase, realizing acceleration of transformation to $\tau $ -phase. The addition of carbon stabilized $\epsilon $ -phase against $\tau $ -phase. The ineffectiveness of in-field annealing for Mn-Al-C is due to the stabilization of $\epsilon $ -phase and the reduction of the Curie temperature. The combination of Zn modification and IFA is realized to synthesize high fraction of $\tau $ -phase for short annealing time and low annealing temperature.

DOI： 10.1109/TMAG.2018.2860559

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Publisher：American Journal of Pathology  

DOI： 10.1016/j.ajpath.2018.09.015

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/14686996.2019.1585143

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DOI： 10.3379/msjmag.1907R002

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DOI： 10.2320/matertrans.M2019019

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Language：Japanese  

DOI： 10.1002/pssb.201800100

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DOI： 10.7567/JJAP.57.0902A6

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Language：English   Publisher：TAYLOR & FRANCIS LTD  

DOI： 10.1080/14686996.2018.1491165

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

FeNi films were directly deposited on MgO(001) substrates by co-sputtering and rapid thermal annealing (RTA). The formation of the L1(0) phase was investigated for films with different thicknesses and different annealing conditions by grazing incidence X-ray diffraction. For the FeNi films with a thickness of 5 nm, superlattice 001 and 110 peaks were observed after annealing at a heating rate of 50 degrees C/s, which indicates that three variants of L1(0) grains were formed in the films. The maximum long-range order parameter, which corresponded to a volume-averaged parameter, was approximately 0.11. For the FeNi films with a thickness of 30 nm, a superlattice 110 peak was only observed after annealing at a heating rate of 50 degrees C/s, and the formation of 001 textured grains was clarified. Magnetic properties also changed depending on the FeNi film structures. The formation mechanism of L1(0)-FeNi is discussed based on the strain caused by RTA in the FeNi films. (C) 2018 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2018.02.318

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Society of Applied Physics  

An epitaxially grown Mn72Ge28 film with a tetragonal crystal structure was fabricated. It was clarified that the film had a perpendicular magnetization and a high perpendicular magnetic anisotropy energy of 14.3 Merg/cm3. The electronic structure was investigated by X-ray magnetic circular dichroism and hard X-ray photoelectron spectroscopy. The obtained X-ray magnetic circular dichroism spectrum revealed that the Mn orbital magnetic moment governed the magnetocrystalline anisotropy of the Mn72Ge28 film. A doublet structure was observed for the Mn 2p3/2 peak of hard X-ray photoelectron spectrum, indicating the spin exchange interaction between the 2p core-hole and 3d valence electrons.

DOI： 10.7567/JJAP.57.04FN10

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Publisher：Annals of Neurology  

DOI： 10.1002/ana.25125

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

L1(0)-ordered FeNi, showing high uniaxial magnetic anisotropy (K-u), is promising as a 'rare metal-free' high K-u material. We have worked on L1(0)-ordered FeNi thin films prepared by two methods: one is molecular beam epitaxy (MBE) with alternate deposition of Fe and Ni monatomic layers, and the other is sputtering with co-deposition or multilayer-deposition of Fe and Ni followed by rapid thermal annealing (RTA). For the MBE films prepared by alternate monatomic layer deposition (leading to the stoichiometric composition: Fe 50 at.%-Ni 50 at.%), a clear relationship between K-u and the long-range order parameter S estimated by synchrotron x-ray diffraction (XRD) was found with maximum values of S = 0.48 and K-u = 7.0 x 10(6) erg cm(-3). The composition dependence of K-u was also investigated by deviating the thickness from monatomic layer, showing a maximum of 9.3 x 10(6) erg cm(-3) around 60 at.% Fe. In addition, the effect of Co addition to L1(0)-ordered FeNi was investigated, suggesting that a small amount (< 10 at.%) of Co substitution for Ni would enhance K-u if S keeps the same. The experiments were in qualitatively good agreement with the first-principles calculations. The magnetic damping constant a was also measured to be approximately 0.01 irrespective of S, suggesting that L1(0)-FeNi is a candidate material with high K-u and low a. For the sputtered films with RTA, no major difference between co-deposition and multilayer-deposition was found: in both cases the formation of L1(0)-ordered phase after RTA was definitely confirmed by XRD. Transmission electron microscopy observations indicated that nanometer-sized L1(0)-ordered clusters were dispersed in a disordered phase, in contrast to that of MBE films showing the homogeneous formation of L1(0)-ordered phase. The enhancement of coercivity (H-c) and residual magnetization (M-r/M-s) was observed associated with the appearance of L1(0)-ordered phase. The maxima of H-c and M-r/M-s were obtained to be 1.35 kOe and 0.22, respectively.

DOI： 10.1088/1361-6463/aa8ff6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Tetrataenite (L1(0)-FeNi) is a promising candidate for use as a permanent magnet free of rare-earth elements because of its favorable properties. In this study, single-phase L1(0)-FeNi powder with a high degree of order was synthesized through a new method, nitrogen insertion and topotactic extraction (NITE). In the method, FeNiN, which has the same ordered arrangement as L1(0)-FeNi, is formed by nitriding A1-FeNi powder with ammonia gas. Subsequently, FeNiN is denitrided by topotactic reaction to derive single-phase L1(0)-FeNi with an order parameter of 0.71. The transformation of disordered-phase FeNi into the L1(0) phase increased the coercive force from 14.5 kA/m to 142 kA/m. The proposed method not only significantly accelerates the development of magnets using L1(0)-FeNi but also offers a new synthesis route to obtain ordered alloys in non-equilibrium states.

DOI： 10.1038/s41598-017-13562-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The anomalous Nernst effect (ANE) in highly ordered Fe4N films was examined in the measurement configuration with an in-plane temperature gradient (del T-x). The anomalous Nernst coefficient (Q(s)) in the case of del T-x parallel to Fe4N[110] was clearly larger than that in the case of del x parallel to Fe4N[100]. Note here that no reports on the Q(s) in Fe4N films have been presented. This anisotropic Q(s) (Q(ani)) was also observed in a different configuration with an out-of-plane temperature gradient. Unlike Fe4N, pure Fe and A2-FeAl systems showed a negligible Q(ani). This Q(ani) might be attributed to the specific hybridization effects between the 3d orbitals of Fe and the 2p orbitals of N. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/APEX.10.073005

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© 2010-2012 IEEE. Magnetic field effects on the transformation from the hexagonal close-packed ϵ-phase to the ferromagnetic L10 τ-phase were evaluated for Mn-Al alloys annealed at 573, 623 and 673 K in magnetic fields up to 15 T. The phase transformation from the ϵ-phase to the τ-phase was enhanced by the magnetic field for the 623 K annealing temperature. These in-field annealing effects are explained by the Zeeman energy of the ferromagnetic τ -phase.

DOI： 10.1109/LMAG.2016.2617859

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The phase formation of ferromagnetic L1(0)-MnAl (tau-phase) was accelerated by annealing in magnetic field. With in-field annealing at 623 K, the magnetization of the t-phase annealed at 15 T was a maximum of 72.2 A.m(2)/kg at 1.5 T, which is over 4 times larger than that annealed without an external magnetic field for the same annealing time. On the other hand, the transformation from tau-phase to beta-phase was suppressed under magnetic field. The obtained bulk sample did not show magnetic anisotropy because of the epsilon-tau solid-state transformation. Obtained results suggested that magnetic field induced acceleration of transformation was due to the gain of Zeeman energy, which increases the driving force of the epsilon-tau transformation.

DOI： 10.2320/matertrans.MAW201709

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have investigated the microstructural evolution and magnetic domain configurations in nano-scale Fe-Ni rich precipitates formed in a single-crystal specimen of Cu-20at%Ni-5at%Fe alloy on isothermal annealing at 873 K and 973 K, using a combination of transmission electron microscopy (TEM), electron backscattering diffraction, field-emission scanning electron microscopy (FE-SEM), and laser-based photoemission electron microscopy (laser-PEEM). The TEM and FE-SEM observations showed that small, spherical solute-rich particles formed randomly in the initial stage of the precipitation, but on isothermal annealing, cubic, rectangular, plate-shaped and rod-shaped precipitates appeared and aligned along the < 1 0 0 > directions in the copper-rich matrix. Laser-PEEM was applied to single-crystal specimens of the alloy and allowed direct observations of magnetic domain configurations in individual ferromagnetic particles at the nanometer scale. This revealed that cubic particles of size approximately 50-60 nm consist of single magnetic domains, but particles of size 100 nm have a closed spin structure (e.g. vortex or multiple domains).

DOI： 10.1088/0022-3727/49/33/335006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We have studied the electronic structure of the L1(o) ordered FePt thin film by hard x-ray photoemission spectroscopy (HAXPES), cluster model, and first-principles calculations to investigate the relationship between the electronic structure and perpendicular magneto-crystalline anisotropy (MCA). The Fe 2p core-level HAXPES spectrum of the ordered film revealed the strong electron correlation in the Fe 3d states and the hybridization between the Fe 3d and Pt 5d states. By comparing the experimental valence band structure with the theoretical density of states, the strong electron correlation in the Fe 3d states modifies the valence band electronic structure of the L1(o) ordered FePt thin film through the Fe 3d-Pt 5d hybridization. These results strongly suggest that the strong electron correlation effect in the Fe 3d states and the Fe 3d-Pt 5d hybridization as well as the spin-orbit interaction in the Pt 5d states play important roles in the perpendicular MCA for L1(o)-FePt. Published by AIP Publishing.

DOI： 10.1063/1.4959957

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

We alternately deposited Ni and Fe monatomic layers on Cu(001) single crystal substrates and also performed surfactant-mediated growth. FeNi films exhibited a large uniaxial magnetic anisotropy (K-u) of over 0.1 MJ/m(3) by using an oxygen or a gold surfactant, although K-u was almost zero without surfactants. Reflection high-energy electron diffraction and atomic force microscopy indicated surfactant effects of oxygen and gold. Synchrotron X-ray diffraction indicated a formation of an L1(o)-type ordered FeNi phase having a large K-u. We have considered that the surfactants enhanced layer-by-layer growth leading to the L1(o)-ordering by changing a diffusion scenario of Fe and Ni atoms. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2016.02.040

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We study the enhanced spin relaxation time of Au nanoparticles in nanopillar-shaped double-barrier junction devices with a stacked Fe/MgO/Au-nanoparticle/MgO/Fe structure. The size of Au nanoparticles located in a current path is deduced from a transmission electron micrograph and the Coulomb blockade behavior in the current-voltage characteristics of the devices. A finite tunnel magnetoresistance (TMR) is observed above a critical current and is attributable to spin accumulation in Au nanoparticles. Based on a simple model of TMR due to spin accumulation in a nanoparticle, the spin relaxation time tau(s) is estimated from the magnitude of the critical current. The temperature and bias-voltage region where TMR appears are determined from systematic observations, showing that the appearance of TMR is not associated with the Coulomb blockade but with spin accumulation. We find that the obtained tau(s) is anomalously extended (similar to 800 ns) at low temperatures and abruptly decreases above a critical temperature. Interestingly, the critical temperature strongly depends on the size of the Au nanoparticles and is much lower than the effective temperature corresponding to the discrete energy spacing. A theoretical analysis for the spin relaxation of electrons with discrete energy levels shows that not only the anomalously extended spin relaxation time, but also the strong temperature dependence of tau(s) arise from the broadening of discrete energy levels due to coupling with phonons in the surrounding matrix. Numerical calculations using reasonable parameter values well reproduce the observed temperature and size dependence of the spin relaxation time in Au nanoparticles.

DOI： 10.1103/PhysRevB.93.085402

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_925

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A new non-chemical method for heteroatom doping into single-layer graphene was demonstrated by high-energy ion irradiation of the graphene-based heterostructure. The heterostructure was fabricated by depositing a LiF layer on a single-layer graphene sheet which was grown on a Cu substrate by chemical vapor deposition. We successfully obtained fluorinated graphene by 2.4 MeV Cu-63(2+) ion irradiation through the LiF overlayer. Raman spectroscopy, near edge X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy revealed that 20%-fluorinated graphene is obtained superior to the defect formation by the high-energy ion irradiation up to 1014 ions per cm(2). It was also shown that the F atoms are chemically adsorbed on single-layer graphene by the C-F bonds in a similar manner to the fluorinated graphene synthesized by the purely chemical route. The mechanism of the fluorination by the ion irradiation is discussed in terms of electronic excitations of carbon and heteroatoms based on the spectroscopic results.

DOI： 10.1039/c6ra09631j

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Language：English   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2502

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.7566/JPSCP.8.034008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Material dependence of the anomalous Nernst effect (ANE) in perpendicularly magnetized ordered-alloy thin films is systematically investigated. The ANE was found to have a tendency to increase simply as uniaxial magnetic anisotropy increased at room temperature. The ANE increases as temperature increases from 10 to 300K for all the materials. However, the signs of the ANE in Fe-based ordered-alloys (L1(0)-FePt and L1(0)-FePd) and in a Co/Ni multilayer are opposite to those in Mn-based ordered-alloys (L1(0)-MnGa and D0(22)-Mn2Ga). Ordered-alloys with larger uniaxial magnetic anisotropies reveal larger ANE and might be desirable for thermoelectric applications. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4922901

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The local structure and magnetism of FeNi alloy films prepared by alternate deposition of Fe and Ni monatomic layers, where perpendicular magnetic anisotropy has been observed, were investigated through Fe-57 nuclear probes using Mossbauer spectroscopy. It was confirmed that the films are composed of L1(0)-type ordered FeNi phase and A1-type disordered FeNi phase. For the films grown at 40-70 degrees C, which have no perpendicular anisotropy, the A1-disordered phase is dominant, whereas for the films grown at 100-190 degrees C, which have a stronger perpendicular anisotropy, the relative amount of the L1(0)-ordered phase reaches 40% or more. It was clearly shown that the magnetic anisotropy of these films is strongly correlated with the local environments of Fe in the films. The results imply that if a further increase in the ratio of the L1(0)-ordered phase is successfully achieved, one would obtain films with a stronger magnetic anisotropy applicable to perpendicular magnetic recording.

DOI： 10.1088/0022-3727/48/20/205002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

FeNi films were fabricated by sputtering and rapid thermal annealing on thermally amorphous substrates to realize the formation of an L1(0)-FeNi phase by a simple method. Structural and magnetic properties of FeNi films were investigated by varying the annealing temperature. L1(0)-FeNi superlattice peaks were not observed in X-ray diffraction patterns, indicating no formation of L1(0)-ordered phase, however, the surface structure systematically changed with the annealing temperature. Magnetization curves also revealed a drastic change depending on the annealing temperature, which indicates the close relation between the morphology and magnetic properties of FeNi films fabricated on amorphous substrates. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4913935

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have investigated comparative experiments for spin injection into semiconductor in an ordered L1(0)-FePt/MgO/n-GaAs hybrid structure using electrical and optical detection methods. Spatial-resolved Kerr rotation microscope image clearly demonstrates accumulation of perpendicularly oriented spins in an n-GaAs channel at zero magnetic field. On the other hand, electrical three-terminal Hanle measurement shows shorter spin lifetime than that of the optical measurement. It suggests that the spin lifetime obtained from three-terminal Hanle method originates from spins at the MgO/GaAs interface but not in the bulk GaAs channel.

DOI： 10.1088/0022-3727/48/16/164003

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_826

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

L1(0)-type ordered FeNi alloy is a good candidate material for rare-earth-free permanent magnets due to its large saturation magnetization, large uniaxial magnetic anisotropy (K-u) and high Curie temperature. Previously, we investigated the fundamental properties of L1(0)-FeNi by preparing single crystal films by alternate deposition of Fe and Ni monatomic layers. In the present study, we investigated the influences of the addition of Co on the magnetic and structural properties of L1(0)-type ordered FeNi films. Three types of Co addition, with the substitution of Fe layers, Ni layers and both layers, were performed. X-ray diffraction using synchrotron radiation indicated that Co atoms were randomly distributed in films in all addition processes. A long-range order parameter of the L1(0)-FeNi phase and K-u showed a tendency to decrease with the amount of Co for additions substituting Fe layers and both layers. However, K-u showed no decrease with Co addition substituting <= 10% of Ni layers, even though the order parameter notably decreased. This indicates that an achievement of the Co addition substituting Ni atoms without any reduction of the order parameter enhances K-u in L1(0)-FeNi.

DOI： 10.1088/0022-3727/47/42/425001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

FeNi with the L1(0)-ordered structure is formed over an astronomical timescale in meteorites. In this study, severe plastic deformation using high-pressure torsion (HPT) is employed for the production of the L1(0) structure in the laboratory. Its formation is confirmed by X-ray diffraction analysis and transmission electron microscopy. Processing of elemental nanopowders by HPT is an effective method for the formation of the L1(0) phase, which is enhanced by the addition of Co to FeNi or annealing after HPT. The formation of the phase must be associated with enhanced diffusion through HPT.

DOI： 10.1080/09500839.2014.955546

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We report ultrahigh-resolution spin-resolved hard X-ray photoemission (HAXPES) for a buried FeNi alloy film. By utilizing the forward Mott scattering in a Au layer on FeNi, our spin-resolved HAXPES method does not require a standard spin detector and allows us to use the multi-channel electron detection system for the high-efficient electron detection as used in conventional photoemission spectroscopy. A combination of the forward Mott scattering and multi-channel detection leads us to measure a clear spin polarization as well as spin-resolved majority and minority states in the Fe 2p core-level spectra without using the standard spin detector. This method enables us to measure spin-resolved core-level spectra for buried ferromagnetic materials. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4868248

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

To understand the hard magnetism of L1(0)-type ordered FeNi alloy, we extracted the L1(0)-FeNi phase from a natural meteorite, and evaluated its fundamental solid-state properties: sample composition, magnetic hysteresis, crystal structure and electronic structure. We executed multidirectional analyses using scanning electron microscopy with an electron probe micro-analyzer (SEM-EPMA), a superconducting quantum interference device (SQUID), x-ray diffraction (XRD) and magnetic circular dichroism (MCD). As a result, we found that the composition was Fe: 50 : 47 +/- 1 : 98 at.%, Ni: 49 : 60 +/- 1 : 49 at.%, and an obvious superlattice peak is confirmed. The estimated degree of order was 0.608, with lattice constants a = b = 3 : 582 angstrom and c = 3 : 607 angstrom. The obtained coercivity was more than 500 Oe. MCD analysis using the K absorption edge suggests that the magnetic anisotropy could originate from the orbital magnetic moment of 3d electrons in Fe; this result is consistent with that in a previous report obtained with synthetic L1(0)-FeNi.

DOI： 10.1088/0953-8984/26/6/064206

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We prepared L1(0)-ordered FeNi alloy films by alternate deposition of Fe and Ni monatomic layers, and investigated their magnetic anisotropy. We employed a non-ferromagnetic Au-Cu-Ni buffer layer with a flat surface and good lattice matching to L1(0)-FeNi. An L1(0)-FeNi film grown on Au6Cu51Ni43 showed a large uniaxial magnetic anisotropy energy (K-u = 7.0 x 10(6) erg cm(-3)). K-u monotonically increased with the long-range order parameter ( S) of the L1(0) phase. We investigated the Fe-Ni composition dependence by alternating the deposition of Fe 1 - x and Ni 1 + x monatomic layers ( -0.4 < x < 0.4). Saturation magnetization (M-s) and K-u showed maxima (M-s = 1470 emu cm(-3), K-u = 9.3 x 10(6) erg cm (-3)) for Fe60Ni40 (x = -0.2) while S showed a maximum at the stoichiometric composition (x = 0). The change in the ratio of lattice parameters (c/a) was small for all compositions. We found that enrichment of Fe is very effective to enhance Ku. The large Ms and Ku of Fe60Ni40 indicate that Fe-rich L10-FeNi is promising as a rare-earth-free permanent magnet.

DOI： 10.1088/0953-8984/26/6/064207

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

FeCo thin films are fabricated by alternate monoatomic layer deposition method on a Cu3Au buffer layer, which in-plane lattice constant is very close to the predicted value to obtain a large magnetic anisotropy constant. The variation of the in-plane lattice constant during the deposition process is investigated by reflection high-energy electron diffraction. The magnetic domain images are also observed by a photoelectron emission microscope in order to microscopically understand the magnetic structure. As a result, element-specific magnetic domain images show that Fe and Co magnetic moments align parallel. A series of images obtained with various azimuth reveal that the FeCo thin films show fourfold in-plane magnetic anisotropy along < 110 > direction, and that the magnetic domain structure is composed only of 90 degrees wall. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4862910

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

To prepare a flat surface of Cu film on Cu3Au(001), we utilized the effect of Au addition to Cu, and investigated the dependence of the growth mode on the amount of Au added. We grew Cu-x%Au (x = 0-20) films on Cu3Au(001) underlayers by co-deposition and observed the surface morphology by scanning tunneling microscopy. For Cu film without Au addition, three-dimensional islands were observed on the surface while flat two-dimensional surfaces were observed for Cu film with only 2.5%Au addition. This difference in the growth mode was found to be due to surface segregation of Au revealed by in situ Auger electron spectroscopy. It was considered that the Au atoms acted like a surfactant and avoided three-dimensional island growth by suppression of the accumulation of epitaxial strain in Cu-x%Au films. However, the terrace size decreased with x. This decrease was thought to be due to an increase in an effective Ehrlich-Schwoebel barrier. The surface flattening effect by addition of another element would be obtained in other systems as well by employing a suitable element. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2013.09.021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We studied on the magnetic damping constants (alpha) for L1(0)-FeNi and disordered FeNi employing three kinds of measurement methods. An L1(0)-FeNi thin film exhibited high perpendicular magnetic anisotropy of 7.1 x 10(6) erg cm(-3). At magnetic fields (H) lower than 2 kOe, alpha was estimated to be 0.091 +/- 0.003. However, it was reduced down to 0.013 +/- 0.001 with H, indicating that extrinsic contributions enhance alpha. The intrinsic alpha = 0.013 +/- 0.001 was comparable to alpha = 0.009 +/- 0.002 for the disordered FeNi. This suggests that L1(0)-FeNi is a candidate achieving high magnetic anisotropy and low magnetization damping simultaneously. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4845035

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Single crystalline Fe-20% Cr film was prepared using a molecular beam epitaxy technique, and 2.4 MeV Cu2+ ion-irradiation was subsequently carried out at room temperature and at 748 K. Magnetic hysteresis measurement and magnetic domain observation showed that room-temperature irradiation did not have a large effect on the magnetic properties of Fe-20% Cr films. However, irradiation at 748 K caused a significant magnetic hardening and a drastic change in domain structures. It is assumed that the domain characteristics reflect the formation of chromium-rich precipitates due to the phase separation accelerated by irradiation. This study demonstrates the feasibility of nondestructive magnetic techniques for evaluating the materials degradation of Fe-Cr alloys under the irradiation environment. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnucmat.2012.11.042

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

Highly L10-ordered FePt thin films with a strong (001) texture were successfully fabricated on amorphous substrates simply by co-sputtering and rapid thermal annealing at a low temperature of 400â°C. The morphology of FePt thin films depended strongly on the heating rate, changing from a continuous structure with an atomically flat surface to an island-like structure. The change of the morphology resulted in a drastic increase of coercivity, indicating that the magnetization process could be controlled by the heating condition. This fabrication method of ordered FePt thin films is favorable in view of the compatibility for a practical device fabrication process. © 2013 Author(s).

DOI： 10.1063/1.4821629

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

Cu-10 at% Ni-5 at% Co specimens containing nano-scale magnetic particles were investigated with respect to the relationship between the microstructure and the magnetic properties, by using a transmission electron microscope (TEM), a SQUID magnetometer and a magnetic thermobalance. The present TEM observations revealed that small magnetic precipitates were formed in a copper matrix in a specific manner that has never been reported in conventional precipitation alloys consisting of non-magnetic elements. The SQUID measurements indicated that a specimen annealed for a short period had a large coercive force, although the force decreased for longer annealing treatments. The magnetic thermogravity scan in the temperature range of 300-1223 K showed that the alloy specimen had a paramagnetic state between two ferromagnetic regions.

DOI： 10.3938/jkps.63.555

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We investigated the magneto-optical (MO) effect with localized surface plasmon resonance (LSPR) on ferromagnetic metal (Fe and Co) nanoparticles. We estimated the electric-field enhancement of the ferromagnetic metal nanoparticles caused by LSPR based on Mie scattering theory and compared it with that of Au nanoparticles. The electric-field enhancement of the ferromagnetic metal nanoparticles was 15-17, which is half of that of the Au nanoparticles. In order to explain the calculated results, we prepared ferromagnetic metal nanoparticles by a self-assembly process. We measured the optical transmission spectra and Faraday effect of the ferromagnetic nanoparticles. Although remarkable MO enhancement was not observed, we found characteristic MO spectra and a peak shift at wavelengths longer than 800 nm in samples whose thickness was less than 6 nm. We numerically investigated the size effect and reproduced the experimental results. We concluded that localized plasmons of ferromagnetic metal nanoparticles can produce electric-field enhancement, but the enhancement is not enough to increase the MO effect, and that the MO effect of nanosized ferromagnetic metals could be influenced by size effects rather than by LSPR. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.073003

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DOI： 10.7567/APEX.6.049201

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We propose a new-type of thermopile consisting of two ferromagnetic materials with anomalous Nernst effects (ANEs) of opposite signs. L1 0-FePt and L10-MnGa have been chosen as the materials because they show large ANEs with opposite signs. The combination of perpendicularly magnetized FePt and MnGa wires enhances the ANE voltage effectively. The ANE in in-plane magnetized FePt films induced by applying a perpendicular temperature difference shows no variation against the film thickness, which is a promising characteristic for thermoelectric applications because the internal resistance of the thermopile, which determines the extractable electric power, can be reduced by increasing the thickness of ferromagnetic wires. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.033003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigated the origin of strong magnetic anisotropy energy (MAE) in L1(0)-type ordered FeNi phase by angular-dependent magnetic circular dichroism. Our findings showed that the orbital magnetic moment of Fe has a significant angular dependence that exhibits a maximum value at the [001] direction corresponding perpendicular to the plane. The calculated uniaxial anisotropy energy when considering spin-orbit (SO) interaction shows quantitatively good agreement with the volume MAE. We concluded that the orbital anisotropy in 3d Fe electrons results in the strong MAE in L1(0)-FeNi and ascribe this to the spin-orbit interaction via structural ordering. (C) 2012 Elsevier BY. All rights reserved.

DOI： 10.1016/j.jmmm.2012.09.008

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DOI： 10.3379/msjmag.1303R019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The atomic structure of extremely small cobalt (Co) nanoparticles embedded in an amorphous carbon (C) matrix has been studied by spherical aberration (C-s) corrected high-resolution transmission electron microscopy and focal-series restoration. The Co nanoparticles, 1-3 nm in diameter, are crystalline with the face centered cubic structure, while the radial distribution function analysis revealed the existence of a Co-C bond. The reconstructed phase images of the exit-wave function clearly show the projected potential distribution within the Co nanoparticles. The C-s-correction has hence a benefit to visualize embedded crystalline clusters unambiguously, which are responsible for the magnetotransport properties of the Co-C films. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765362]

DOI： 10.1063/1.4765362

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NORTHWEST INST NONFERROUS METAL RESEARCH  

A series of Co-doped amorphous carbon granular thin films with various Co contents (x, at%) were deposited on n-type Si (100) substrates by a magnetron co-sputtering technique at room temperature. The microstructure, magnetotransport and magnetic properties of the Co-C films have been characterized. By optimizing Co content, giant negative magnetoresistances (MRs) were observed at low temperature, with a maximum MR ratio of 27.6% at 2 K under an applied magnetic field of 90x79.6 kA.m(-1) for the film with Co content of 6.4 at%. As Co content increases from 6.4 at% to 16.4 at%, the MR ratio decreases gradually from 27.6% to 2.2%. A linear In rho-T-1/2 relationship indicates that the spin transport in Co6.4C93.6 thin film agrees well with tunneling conductance.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The spin torque oscillation (STO) due to magnetic resonance is investigated in term of the Landau-Lifshitz-Gilbert (LLG) equation. An analytic formula of the LLG equation with macro-spins describes a spin state that involves information of an oscillation frequency. The LLG equation can be transformed into an equation of a forced oscillation. The obtained equation includes a frequency of STO, an effective Gilbert damping factor, and an injected spin current. We show that the effective Gilbert damping is given by a linear function of the spin current. Contrastingly, the frequency of STO is not affected by the injected spin current. However, the time-dependent variation of the spin current, e. g., the pulsated spin current, possibly increases the frequency of STO.

DOI： 10.1109/TMAG.2012.2201700

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The anomalous Nernst effect in a perpendicularly magnetized L1 0-ordered epitaxial FePt(001) thin film has been investigated, and the anomalous Nernst coefficient and the anomalous Nernst angle of the FePt thin film were experimentally evaluated. Furthermore, the voltage due to the anomalous Nernst effect in the spin-Hall device was simulated by the finite element method. A good agreement between the experiment and the simulation was found. It was revealed that the anomalous Nernst effect could be quantitatively discussed even in nanoscale devices. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.5.093002

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Language：Japanese   Publisher：公益社団法人 応用物理学会  

DOI： 10.11470/jsapmeeting.2012.2.0_1984

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Barrier-height (BH) imaging using scanning tunneling microscopy (STM) was used to study the growth of Co films on Au(001) surfaces. We have observed BH of metastable bcc Co film (>1 ML) for the first time, and that showed a large BH value (similar to 6 eV), whereas the observed BH of the Au(001) surface (similar to 3.5 eV) was consistent with the previous results. The origin of the large BH was qualitatively understood by considering that 3d electrons for tunneling are dominant for the Co(001) surface. We have observed numerous islands with different sizes and heights after 0.15 ML Co coverage and successfully obtained, from the BH imaging, an element-specific contrast, i.e. recognizing aggregated Au islands and Co islands, and information about inhomogenities of BH with proper consideration of the artifacts near the step edges. The height modification by the large BH difference is discussed.
STM/BH studies of FePt films revealed two kinds of monolayer heights, the sum which was equal to the c axis lattice constant of L1(O) FePt. Two different dl/dz signal levels were observed on atomically flat terraces. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2011.09.023

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We investigated the MgO layer thickness dependences of the structure and magnetic properties of L1(0)-FePt/MgO/GaAs structures. To examine how the crystallinity and growth morphology of the MgO layer affect the L1(0)-FePt layer, two kinds of preparation method were employed for MgO deposition: electron beam (EB) evaporation and sputter deposition. The MgO layer deposited by EB evaporation included a large strain because of the cube-on-cube epitaxial relationship despite a large lattice mismatch between MgO and GaAs. For the MgO layer prepared by sputtering, on the other hand, an amorphous MgO layer was initially grown on the GaAs substrate. Subsequently, a crystalline MgO layer was grown in the (001) direction. In the case of the EB-deposited MgO, as the MgO layer thickness increased, the degree of chemical order of the L1(0)-FePt layer increased from 55 to 81% owing to the improvement of the crystallinity of the MgO layer. The improvement of chemical order also led to the increase in the remanent magnetization of L1(0)-FePt from 84 to 98%. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.02BM05

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

L1(0)-FeNi films were grown by alternate monatomic layer deposition on Au-Cu-Ni buffer layers at several substrate temperatures (T-s), and the relation between the uniaxial magnetic anisotropy energy (K-u) and the long-range chemical order parameter (S) was investigated. A large K-u of (7.0 +/- 0.2) x 10(6) erg/cm(3) and S of 0.48 +/- 0.05 were obtained. The value of K-u was larger than those reported previously for artificially synthesized FeNi films. It was first found that both K-u and S increased with T-s, and K-u was roughly proportional to S. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.010204

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Ferromagnetic resonance (FMR) of epitaxial FePt thin films with in-plane magnetization was investigated by measuring the reflection coefficient (S-11) using coplanar waveguides. FMR signals of four FePt films grown on MgO (001) substrates with different post-annealing temperatures were measured, and the resonant peaks of FePt were successfully observed. Annealing temperature dependence was found in the peak frequency shift depending on the magnetic field applied in the film-plane, which is attributable to the difference of magnetic anisotropy of FePt thin films.

DOI： 10.4028/www.scientific.net/KEM.508.261

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CoxC1-x granular films were deposited on Si substrates by a co-sputtering method. A large negative MR of 30.3% was obtained at 2 K for the sample prepared with the sputtering power of 50 W (C) and 4 W (Co). We have studied structural properties of Co-C granular films by Raman spectroscopy. Two peaks (D and G modes) from carbon bonds were clearly observed, and the intensity ratio of two peaks changed with the sputtering power, suggesting that the graphitization was promoted with the sputtering power. It was also revealed that the transport mechanism changed from tunneling to Mott's variable range hopping and MR decreased with the sputtering power. © 2012 Materials Research Society.

DOI： 10.1557/opl.2012.1467

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The rf oscillation induced in a current-perpendicular-to-plane device with Co2MnSi (CMS) layers by spin-transfer torque was investigated to enhance the rf output power due to the large magnetoresistance (MR) ratio. A large MR ratio of 12.5% was obtained due to the large spin-polarization of CMS, and fundamental and second harmonic rf oscillations were clearly observed in the CMS layer. A high rf output power of 1.1 nW was achieved in spite of a small precession angle of 8.6 degrees. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624470]

DOI： 10.1063/1.3624470

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Language：Chinese   Publishing type：Research paper (scientific journal)   Publisher：NORTHWEST INST NONFERROUS METAL RESEARCH  

Co-C nanocomposite thin films with Co content of 6.4 at%-16.4 at% were fabricated by magneton co-sputtering. TEM images show that the Co nanoparticles are dispersed uniformly in a carbon matrix, indicating typical granular characteristics. The average Co particle size is enlarged by increasing the Co content. Magnetic hysteresis loops reveal that, as Co content increases, magnetization of Co-C thin films is enhanced distinctly. The samples show high magnetization at low temperature and low magnetization at room temperature. Negative MR of 9.1%, 4.3% and 1.9% were observed for Co-C nanocomposite thin films with Co contents of 6.4 at%, 8.3 at% and 9.6 at%, respectively, at 4.2 K under an applied field of 90x79.6 kA.m(-1). The MR value is decreased with increasing Co content, which can be attributed to the evolution of microstructure.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The electromagnetic properties of a Cu-75-Fe-5-Ni-20 alloy have been investigated upon isothermal annealing of the alloy at 873 K, using a superconducting quantum interference device (SQUID) magnetometer and a physical property measurement system (PPMS) instrument. Magnetoresistance (MR) was closely related to the magnetization value in specimens of the alloy. The most striking finding of the present work is that the as-quenched specimen with no visible precipitates attains the largest MR (similar to 16% at H = 7T and T = 10 K), although fine precipitates with a proper size were thought to be essential in our previous studies. The present investigation also revealed that several significant effects accompanied the magnetic and magnetoresistive properties, with microstructural evolution occurring during the phase decomposition of a Cu-75-Fe-5- Ni-20 alloy. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.045807

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Ferromagnetic resonance measurements of Fe nanodots epitaxially grown on a MgO layer were carried out using a coplanar waveguide to investigate the dynamic behaviours of spins in a magnetic dot assembly. The resonant peaks of Fe nanodots with an average diameter of 10 nm were successfully observed, and a strong magnetic anisotropy was found in the peak frequency shift depending on the magnetic field applied in the film plane. A difference was clearly seen in the peak shift behaviour between Fe nanodots and continuous Fe thin films. The Gilbert damping parameter of the Fe nanodots (nominal thickness: 3 nm) was estimated to be 0.008 12 from the width of the resonant peaks, substantially larger than that of a continuous Fe thin film with a thickness of 8 nm. This difference in damping is attributed to the distribution of the effective field in each nanodot due to size dispersion. Ferromagnetic resonance studies using coplanar waveguides thus enable clarification of the spin dynamics of magnetic dot arrays and the fundamental spin dynamics of a single nanodot.

DOI： 10.1088/0022-3727/44/6/064007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

Epitaxial <i>L</i>1₀-ordered FeNi thin films were artificially fabricated on a nonmagnetic AuNi buffer layer by using an alternate monatomic layer deposition. A uniaxial magnetic anisotropy energy of the FeNi layer was estimated to be 5.8 × 10⁶ erg/cm³ from magnetization measurements, which is the largest energy among values reported on FeNi thin films grown on nonmagnetic buffers. A long-range order parameter of the FeNi layer was estimated to be 0.330 from a grazing incidence X-ray diffraction (GI-XRD) using synchrotron radiation. We also investigated the relation between the ratio of c-axis lattice constant to a-axis lattice constant (c/a ratio) and the uniaxial magnetic anisotropy energy of FeNi thin films grown on several buffer layers. The uniaxial magnetic anisotropy energy monotonically increased with the increase in the c/a ratio, whereas the anisotropy had no clear relation with the long-range order parameter. Not only the improved long-range order parameter but optimized c/a ratio in FeNi are expected to lead to the enhancement of the perpendicular magnetic anisotropy.

DOI： 10.3379/msjmag.1106R008

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Magnetic domain structure of L1(0)-type FeNi is observed by angular dependent photoelectron emission microscopy. It reveals the perpendicular magnetic component in magnetic domain structure with Bloch wall. The formation of Bloch wall is ascribed to the large magnetic anisotropy energy of L1(0)-FeNi.

DOI： 10.1088/1742-6596/266/1/012095

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

An FeNi film with a metastable L1(0)-ordered phase was fabricated by an alternate monatomic layer deposition. An Fe monolayer and a Ni monolayer were alternately grown on a Cu0.6Ni0.4 binary buffer layer. A (001) L1(0)-FeNi superlattice peak, which indicates the formation of a L1(0) phase, was clearly observed by an X-ray diffraction. A long-range order parameter S of L1(0)-FeNi was estimated to be 0.5 +/- 0.1. It was found that the film has a uniaxial magnetic anisotropy along c-axis by magnetization measurement. The uniaxial magnetic anisotropy energy K-u was evaluated to be (5.0 +/- 0.1) x 10(6) erg/cc.

DOI： 10.1088/1742-6596/266/1/012119

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We have carried out an investigation of surface structures of Cr nanoparticles grown on a MgO layer for studying single electron tunneling (SET). Reflection high-energy electron diffraction pattern changes from spotty to streak with decreasing Cr nominal thickness, while Cr forms nano size particles with the size of around 3.5 nm in diameter for all the samples. The double tunnel junctions for the Cr nominal thickness of 0.1 nm show clear Coulomb blockade with the threshold voltage of 50 mV, indicating that this Cr nanoparticle satisfies the condition for the appearance of SET. The relatively large volume of the Cr nanoparticles may be related with the fact that tunnel magnetoresistance due to spin accumulation in Cr nanoparticles is small.

DOI： 10.1088/1742-6596/266/1/012093

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We have studied spin-dependent single electron tunneling in Cr nanoparticles with a diameter of 4 nm using Fe/MgO/Cr-nanoparticles/MgO/Fe double tunnel junctions. The transport properties are governed by the Coulomb blockade, showing suppression of current at low bias voltages. Magnetoresistance is clearly observed at a bias voltage over 0.25 V, and the magnetoresistance ratio increases with increasing bias voltage. These results suggest that the magnetoresistance is due to the spin accumulation in Cr nanoparticles. With some assumption, the minimum value of spin relaxation time in Cr nanoparticles is roughly estimated to be on the order of tens of nanoseconds.

DOI： 10.1109/TMAG.2010.2044870

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Co-C granular thin films with a Co content of 6.4 at.% were deposited at room temperature by co-sputtering. The magnetotransport properties of the thin films were investigated within 2-300 K under magnetic fields up to 90 kOe. A large negative magnetoresistance (MR) of 27.6% was successfully observed at 2 K. As temperature (T) increased, negative MR decreased drastically. Meanwhile, positive MR with an organic MR (OMAR)-like shape emerged in a low magnetic field region. Ordinary MR (OMR) appeared in a high magnetic field region and can be verified by MR proportional to H(2) fitting. When reached 10 K, MR became completely positive. The MR effect showed strong temperature dependence. The interesting phenomena may help us gain a new insight into the spin-dependent transport in ferromagnetic metal (FM)/amorphous-carbon (alpha-C) system.

DOI： 10.1109/TMAG.2010.2043340

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L1(0)-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L1(0)-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L1(0)-FeNi thin films. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3337649]

DOI： 10.1063/1.3337649

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The energy bandgap of an insulator is large enough to prevent electron excitation and electrical conduction. But in addition to charge, an electron also has spin, and the collective motion of spin can propagateand so transfer a signalin some insulators. This motion is called a spin wave and is usually excited using magnetic fields. Here we show that a spin wave in an insulator can be generated and detected using spin-Hall effects, which enable the direct conversion of an electric signal into a spin wave, and its subsequent transmission through (and recovery from) an insulator over macroscopic distances. First, we show evidence for the transfer of spin angular momentum between an insulator magnet Y 3 Fe 5 O 12 and a platinum film. This transfer allows direct conversion of an electric current in the platinum film to a spin wave in the Y 3 Fe 5 O 12 via spin-Hall effects4-11. Second, making use of the transfer in a Pt/Y 3 Fe 5 O 12 /Pt system, we demonstrate that an electric current in one metal film induces voltage in the other, far distant, metal film. Specifically, the applied electric current is converted into spin angular momentum owing to the spin-Hall effect in the first platinum film; the angular momentum is then carried by a spin wave in the insulating Y 3 Fe 5 O 12 layer; at the distant platinum film, the spin angular momentum of the spin wave is converted back to an electric voltage. This effect can be switched on and off using a magnetic field. Weak spin damping in Y 3 Fe 5 O 12 is responsible for its transparency for the transmission of spin angular momentum. This hybrid electrical transmission method potentially offers a means of innovative signal delivery in electrical circuits and devices. © 2010 Macmillan Publishers Limited. All rights reserved.

DOI： 10.1038/nature08876

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Effects of the molecule-adsorption on a MgO surface on the growth of ultra-thin Fe films were investigated. Surface observation by reflection high-energy electron diffraction and ultra-high vacuum atomic force microscopy showed that the adsorption of molecules on the MgO surface affected the morphology of Fe films grown on the MgO surface. It was revealed that the surface flatness of Fe films was improved by appropriate molecule-adsorption on the MgO surface. [doi: 10.2320/matertrans.M2009218]

DOI： 10.2320/matertrans.M2009218

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

In the field of spintronics, researchers have manipulated magnetization using spin-polarized currents(1-3). Another option is to use a voltage-induced symmetry change in a ferromagnetic material to cause changes in magnetization or in magnetic anisotropy(4-14). However, a significant improvement in efficiency is needed before this approach can be used in memory devices with ultralow power consumption. Here, we show that a relatively small electric field (less than 100 mV nm(-1)) can cause a large change (similar to 40%) in the magnetic anisotropy of a bcc Fe(001)/MgO(001) junction. The effect is tentatively attributed to the change in the relative occupation of 3d orbitals of Fe atoms adjacent to the MgO barrier. Simulations confirm that voltage-controlled magnetization switching in magnetic tunnel junctions is possible using the anisotropy change demonstrated here, which could be of use in the development of low-power logic devices and non-volatile memory cells.

DOI： 10.1038/NNANO.2008.406

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We report on an electrical detection of current driven domain wall (DW) deformation induced by a current pulse injection in arc-shaped permalloy (Py) submicron wires. Current polarity and pulse length dependence were investigated under an assisting external magnetic field. Initial DW states prepared by an application of a large magnetic field were distributed to two distinct DW states. A current pulse application promoted transition between them. In addition, the third DW state was established only by an application of the short pulses (&lt; 50 ns). This result suggests the possibility of the high-speed control of the DW dynamics. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200777255

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Magnetization, electrical conduction, and magnetoresistance (MR) of C(60)-Co nanocomposites, where Co nanoparticles are dispersed in C(60) molecules, have been investigated over a wide temperature range and Co volume fraction. The C(60)-Co nanocomposites exhibit MR when the Co volume fraction is controlled in such a way that the conduction mechanism is dominated by tunneling of carriers between Co nanoparticles in the C(60) matrix. The MR, which is attributed to spin-polarized tunneling through the C(60) molecules, shows strong temperature dependence. Our results indicate that some paramagnetic components contribute to the observed MR. The material-dependent bias-voltage dependence of the MR ratio suggests that these paramagnetic components originate from the interface between organics and ferromagnets. The present study advances the fundamental understanding of spin-dependent transport in organic semiconductors.

DOI： 10.1103/PhysRevB.76.214414

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We demonstrate fabrication of rubrene-Co nano-composites, yielding an introduction of a spin degree of freedom in rubrene-based, electronics devices, and report on large magnetoresistance (MR) ratio of 78% at 4.2 K. It is elucidated that the observed MR effect is ascribed to the magnetization of the Co nano-particles, and this indicates spin-dependent transport via rubrene molecules is achieved. In addition, the MR effect can be observed even at room temperature. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2007.09.061

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We investigated the annealing temperature dependence of differential tunneling conductance spectra (dI/dV as a function of V) in CoFeB/teXtUred MgO(001)/CoFeB magnetic tunnel junctions (MTJs) that exhibit the giant tunneling magnetoresistance (TMR) effect at room temperature. The spectra were strongly affected by annealing the MTJs. A reduction in dI/dV at around 300 mV was observed only in annealed MTJs in which the CoFeB electrodes were crystallized in a bcc(001) structure. Because the reduction in conductance was observed in both MTJs that have a 1.8-nm-thick MgO barrier and MTJs that have a 3.2-nm-thick MgO barrier, we concluded that Delta(5) and Delta(2') evanescent states, which rapidly decay in the MgO tunneling barrier, are not the cause of the reduction in conductance. We believe the cause of the reduction is either the electronic structure of the interfaces between MgO(001)/bcc CoFeB(001) after annealing or a particular feature of Delta(1) states in MgO(001) or bee CoFeB(001). () 2007 Published by Elsevier Ltd

DOI： 10.1016/j.ssc.2007.07.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

An influence of spin-transfer-induced resonant excitation of a vortex magnetic domain wall on magnetization reversal process was investigated in Permalloy nanowires. Sizable reduction of the depinning field was observed under an application of radio frequency current when the frequency coincided with resonance of the vortex core. The resonant frequency was found to increase by shrinking the wire width. These results lead the authors to conclude that the spin-transfer-induced resonant excitation assists the depinning of the vortex domain walls. This provides an important insight for the realization of novel magnetic memory and logic devices based on current-driven domain wall manipulation.

DOI： 10.1063/1.2772174

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The authors have observed magnetoresistance (MR) ratios of 12% and 0.1% at 4.2 and 290 K, respectively, in a nanocomposite in which Co nanoparticles are embedded in the fine molecular structure of a tris(8-hydroxyquinoline) aluminum (Alq(3)) matrix. Structural analyses, magnetization measurements, and conduction properties of the device reveal that the MR effect is induced by spin-dependent transport in the Alq(3). (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2769748

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Topological surface analysis using in situ scanning tunneling microscopy was performed for highly oriented polycrystalline (textured) MgO(001) tunneling barrier layers grown on amorphous CoFeB electrode layers. The microscopy revealed a MgO surface structure in which nanosized grains were dispersed on clusters that originated from the CoFeB underlayer. In situ annealing reduced this surface roughness. Local tunneling spectroscopy measurements revealed the formation of a nearly perfect and uniform tunneling barrier in spite of grain boundaries in the textured MgO(001) layer, which is consistent with the fact that textured CoFeB/MgO/CoFeB and fully epitaxial MgO-based magnetic tunnel junctions exhibit comparable spin-dependent tunneling properties. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2754372

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We measured differential conductance spectra of magnetic tunnel junctions (MTJs) with thin MgO barrier and low-resistance area product. The spectra of MTJs with MgO barrier thicker than 1.05 nm were essentially the same except for slight decrease of contributions from low-energy excitations, such as magnons. The spectra of MTJ with 1.01 nm MgO barrier were thoroughly different from the MTJs with thicker barrier. The result reveals that an MTJ with very thin MgO barrier thickness has different conduction characteristics from those with thicker MgO barriers. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.773

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SCIENTIFIC PUBLISHERS  

The surface morphology of epitaxial Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions, which show the giant tunneling magnetoresistance effect, was investigated by in situ scanning tunneling microscopy. It was observed that an epitaxial MgO barrier layer forms flat surface structures. The surface was flatter with distinct steps and terraces after annealing, which would lead to an increase of the tunneling magnetoresistance ratio. Examination of the local electronic structures of 1.05-nm-thick MgO barrier layers by scanning tunneling spectroscopy revealed no pinholes in the layers, so they would be perfect barriers in magnetic tunnel junctions.

DOI： 10.1166/jnn.2007.017

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

Ferromagnetic resonance (FMR) measurements using coplanar waveguides (CPWs) make it possible to perform highly sensitive magnetization measurements, since a CPW can concentrate electromagnetic waves onto a narrow signal line. In this study, we aimed to perform FMR measurements of a minute individual magnet, and investigated the dependence of the sensitivity on the signal line width. We fabricated CPWs on MgO wafers and placed an individual NiFe dot on each of CPWs. NiFe dots with a thickness of 30 nm and various lateral sizes, i.e. 50 × 100, 50 × 80, 50 × 30, 50 × 20, and 50 × 10 μm, were fabricated. The signal line widths of these samples were 150, 100, 50, 30, and 15 μm, respectively. The external magnetic field dependence of the resonance frequency was well fitted by Kittel's formula. As expected, we obtained larger signals from smaller samples, because narrower signal lines that create larger rf fields were employed for smaller samples.

DOI： 10.3379/jmsjmag.31.435

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

C-60-Co nano-composites, in which Co nano-particles are embedded in C-60 molecules, have been fabricated and a magnetoresistance (MR) ratio of 8% has been observed at T = 4.2 K. In addition, we have succeeded in observing a clear MR curve even at room temperature (RT). The MR effect is ascribed to magnetization of the Co nano-particles and spin-dependent transport in C-60 molecules. This study directly indicates that RT operation of molecular spin devices can be realized.

DOI： 10.1143/JJAP.45.L717

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The microscopic structures of MgO(001) barrier layers in magnetic tunnel junctions showing giant tunneling magnetoresistance were characterized by in situ scanning tunneling microscopy. The MgO thin films formed exceedingly flat surfaces, and their terraces were made even flatter by annealing after deposition. This flattening of MgO surfaces apparently promotes coherent transport of electrons, which should enhance the tunneling magnetoresistance ratio. Local tunneling spectroscopy revealed that an annealed MgO layer has a critical thickness between 3 and 5 ML (monolayer), and a continuous film without pinholes can be formed over the thickness. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2213953

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Language：Japanese   Publisher：キヤノンアネルバ  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Scanning tunneling microscopy observations of a single-crystal Fe(001)/MgO(001)/Fe(001) magnetic tunnel junction which shows a large tunnel magnetoresistance effect were performed. Step-and-terrace structures of an epitaxial MgO barrier layer, which are very similar to surfaces of a bottom Fe underlayer, were observed. This indicates that the MgO terraces were grown flatly on each terrace of the Fe electrode. It is supposed that these atomically flat terraces enable a coherent tunneling of electrons through magnetic tunnel junctions. (C) 2006 American Institute of Physics.

DOI： 10.1063/1.2170069

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Tunneling spectroscopy measurements of magnetic tunneling junctions including two different barrier layers were performed. Intense dips at bias voltages of +/- 0.3 V were observed in second derivative conductance spectra only for a magnetic tunneling junction with a MgO barrier. It was concluded that the electronic structure of the MgO barrier has significant influence on the tunneling process of electrons through magnetic tunnel junctions. (C) 2006 American Institute of Physics.

DOI： 10.1063/1.2171961

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In this work, geometric structures for diluted magnetic semiconductor (Ga,Cr)As films grown by low-temperature molecular beam epitaxy were investigated by fluorescence extended X-ray absorption fine structure (EXAFS) measurements. The XAFS analysis has revealed that the majority of Cr atoms in the (Ga,Cr)As film substitute the Ga atoms in the GaAs lattice up to the Cr content x = 0.145. The abrupt change of the Cr-As bond lengths was observed between Cr content x = 0.06 and 0.145, which is due to inhomogeneous distribution of Cr atoms in GaAs matrix. It is expected that the paramagnetic behavior at room temperature in the samples above x = 0.145 is due to the inhomogeneous distribution of the Cr atoms doped in the GaAs matrix. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.12.164

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We measured differential tunneling conductance (dI/dV, d(2)I/dV(2)) spectra of spin-valve-type magnetic tunnel junctions (MTJs) with a MgO(001) tunnel barrier layer and amorphous CoFeB ferromagnetic electrodes that show 315% magnetoresistance (MR) ratio at 4.3 K. The dI/dV spectra showed clear reduction in the conductance at around +/- 400 mV for a parallel magnetic configuration. Such anomalous spectra have never been observed for MTJs with an amorphous Al-O barrier. The d(2)I/dV(2) spectra showed several distinct peaks between 5 and 100 mv. Magnon excitations are assigned to an origin of those peaks and thought to be a dominant process to reduce MR at finite bias voltage. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2005.08.032

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Observation using in situ scanning tunneling microscopy of the layers constituting a magnetic tunnel junction with a naturally oxidized aluminum barrier layer revealed an extremely flat aluminum-oxide surface. It was clarified from line-scan images that the aluminum-oxide barrier layer has atomic steps. This flatness, which is surprising given that the aluminum-oxide film is amorphous, reduced electron scattering within the barrier, leading to momentum-dependent tunneling, which should enable the fabrication of advanced devices, such as spin-polarized resonant tunneling transistors. (C) 2005 American Institute of Physics.

DOI： 10.1063/1.2108121

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

In this work, geometric structures for ferromagnetic nanoscale zinc-blende MnAs dots grown on a sulfur-passivated GaAs(001) were investigated by using fluorescence EXAFS measurement. EXAFS measurements revealed that MnAs dots grown on GaAs(001) substrate did not form NiAs-type structure but zinc-blende structure. The Mn-As bond length in the MnAs dots is about 2.48 angstrom, which is close to that which was estimated from lattice constant of zinc-blende MnAs obtained by density-functional calculations. Existence of zinc-blende MnS (beta-MnS) phase was also observed by EXAFS measurements.

DOI： 10.1238/Physica.Topical.115a00431

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TRANS TECH PUBLICATIONS LTD  

Magnetoresistive switch effect (MRS effect) devices containing two gold (Au) electrodes with a gap less than 2 gm were successfully fabricated on semi-insulting GaAs substrates by wet etching method. Huge MRS effect was observed. Magnetoresistance (MR) ratio reached 1,000,000% under the magnetic filed of 1.5 T when the devices were operated just above the threshold voltage. The magnetic field sensitivity at small magnetic fields was significantly improved. MR ratio of more than 1000% was achieved at 0.03 T. A relative high MR ratio of 100,000% under the magnetic filed of 1.5 T was also achieved when the devices operating before the threshold voltage.

DOI： 10.4028/www.scientific.net/MSF.475-479.2223

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DOI： 10.1238/Physica.Topical.115a00431

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Publishing type：Research paper (scientific journal)  

In this work, geometric structures for ferromagnetic nanoscale zinc-blende MnAs dots grown on a sulfur-passivated GaAs(001) were investigated by using fluorescence EXAFS measurement. EXAFS measurements revealed that MnAs dots grown on GaAs(001) substrate did not form NiAs-type structure but zinc-blende structure. The MnAs bond length in the MnAs dots is about 2.48 Å which is close to that which was estimated from lattice constant of zinc-blende MnAs obtained by density-functional calculations. Existence of zinc-blende MnS (β-MnS) phase was also observed by EXAFS measurements. © Physica Scripta 2005.

DOI： 10.1238/Physica.Topical.115a00431

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The epitaxial growth of zinc-blende CrAs/GaAs multilayers has been achieved by using the molecular-beam epitaxy method. The crystallographic quality was evaluated by reflection high-energy electron diffraction (RHEED) and cross-sectional transmission electron microscopy (TEM). The increase of the substrate temperature during growth up to 300degreesC brings the RHEED pattern to a streak, in contrast to the case at 200degreesC. TEM images show the atomically flat surface and interface of the multilayer.

DOI： 10.1088/0953-8984/16/48/010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Gold (Au)/semi-insulating (SI)-GaAs Schottky diode was fabricated by the standard photolithography method using wet etching. Magnetic-field-dependent avalanche breakdown phenomena were observed in the current-voltage curves measured under magnetic field. The avalanche breakdown due to impact ionization was postponed to higher electrical field under applied magnetic field. Accordingly, threshold voltages of avalanche breakdown increased with the applied magnetic field. Above 0.2 T, avalanche breakdown was totally quenched. When Au-SI-GaAs Schottky diode was operated above the threshold voltage, giant mangetoresistive effects up to 100 000% were achieved under magnetic field of 0.8 T. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1834733

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report on the density dependence of the morphology and electronic structure of zinc-blende-type MnAs dots using in situ photoemission spectroscopy combined with molecular-beam epitaxy. Transmission electron microscopy images showed the zinc-blende-type crystalline structure of 10-nm diameter for each dot on sulfur-passivated GaAs(001) surface. The valence-band photoemission spectra of the MnAs dots were similar to those of the diluted magnetic semiconductor Ga1-xMnxAs. With increasing dot density, the characteristic spectra of the zinc-blende-type MnAs persist but a weak Fermi edge appears, suggesting a metallic behavior as a result of percolation between the dots or the appearance of hexagonal MnAs as a minority phase.

DOI： 10.1103/PhysRevB.70.233305

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Nanometer-scale structures were fabricated by anodic oxidation using scanning probe microscopes on thin-films of various 3d-metal compounds and alloys on GaAs, such as MnAs, MnSb, Cr2O3, CoCr and NiFe. Material variation advances the developments in nano-fabrication by scanning probe microscope. Comparing the oxidation conditions, new methodology for fabrication of nano-devices is explored. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2004.05.067

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Dynamic magnetic properties of epitaxial MnAs thin films are studied by means of Brillouin light scattering (BLS). The sharp spectral peaks of the inelastic BLS are observed in room temperature, which are attributed to surface spin waves indicating the long-wavelength collective behavior of ferromagnetic spins. The field dependence of the surface spin-wave frequency is strongly affected by an in-plane angle between the crystal axis and the external field direction in a GaAs(100)/MnAs(-1100) film, which originates from uniaxial magnetic anisotropy parallel to the MnAs[11-20] axis and the modified g value. Significant damping of the spin-wave BLS spectrum is observed with increasing excitation laser power, possibly due to thermal effects. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1682951

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Smooth Fe78Si10B12 thin films were prepared by r.f. sputtering with the very slow deposition rate of 0.59 nm/min. The as-deposited films were not fully amorphous, instead alpha-Fe(Si) nanocrystallites were found to be embedded in the amorphous matrix. The saturation magnetostriction lambda(s) of the as-deposited film is about 6.5 x 10(-6). After annealing at 540 degreesC for 1 h in an ultrahigh vacuum (4.5 x 10(-5) Pa), the fraction of alpha-Fe(Si) crystalline phase largely increased, and correspondingly the lambda(s) decreased to 4.5 x 10(-7). Ripple domain structures were observed in the as-deposited film, while dense stripe domains were observed in the annealed sample, characterized by a very narrow domain width of 80 nm. (110) texture and island-like configuration of alpha-Fe(Si) nanocrystallites formed by the annealing treatment are responsible for the perpendicular anisotropy. For the as-deposited film, the magnetization curves increased linearly with the increase of the magnetic field, and showed the very small hysteresis. On the other hand, the annealed sample clearly showed a very steep jump near the origin, which is due to the switch process of the dense stripe domain. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2004.02.036

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Zinc-blende type nanoscale MnAs dots were grown on a sulfur-passivated GaAs (0 0 1) surface by molecular beam epitaxy. We report on the dot density dependence of the X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) in the Mn 2p core-level region. The XAS spectrum of low-density MnAs dots showed "localized'' behavior as in the case of (Ga, Mn) As, while the spectrum of high-density MnAs dots changed to metallic behavior. The magnetic-field dependence of the XMCD revealed ferromagnetic behavior in the case of high-density MnAs dots. (C) 2003 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.803

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Smooth Fe78Si10B12 thin films were prepared by RF sputtering with a very slow deposition rate of 0.59nm/min. The as-deposited films are not fully amorphous, instead alpha-Fe(Si) nanocrystallites are found to embed in the amorphous matrix. Ripple domain structures are observed in the as-deposited film. After annealing at 540degreesC for 1 h in an ultrahigh vacuum (4.5 x 10(-5) Pa), dense stripe domains are observed, characterized by a very narrow domain width of 80 nm. (110) texture and island-like configuration of alpha-Fe(Si) nanocrystallites during annealing treatment are responsible for the perpendicular anisotropy. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.764

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Huge magnetoresistance (MR) effect was observed in Au/GaAs films with a nano-size trench fabricated by a focused ion beam process. Positive MR effect with the ratio of 32,000% was obtained in the magnetic field of 15,000 Oe at room temperature. This huge MR effect is promising for the application to spintronic devices such as magnetic sensors. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.285

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We have investigated the electronic structure of Zn1-xMxO (M: 3d transition metal) by x-ray absorption spectroscopy. Using configuration-interaction cluster-model analyses, electronic structure parameters have been deduced and their chemical trend is discussed. Results show that the p-d exchange constant Nbeta is negative and large in cases of Mn, Fe, and Co, which is consistent with the enhancement of magnetic circular dichroism. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1652248

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Au/GaAs magnetoresistive-switch-effect (MRS effect) devices were successfully fabricated by the wet etching method. A large MRS effect was observed. In the current-voltage curves, the current jumped steeply at a threshold voltage of 32.0 V. The threshold voltages shifted to higher values and became less steep with increasing magnetic field. Above 2,000 Oe, no current jump driven by the applied voltage could be observed. The magnetoresistance (MR) ratio reached 1,000,000% at 15,000 Oe when the devices were operated above the threshold voltage. Also magnetic field sensitivity was greatly improved. To achieve a 1000% MR ratio, only 300 Oe was required at 32.2 V.

DOI： 10.1143/JJAP.43.2101

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Strong magnetic poles at characteristic rectangular defects have been observed using a magnetic force microscope on a MnAs((1) over bar 1 0 0) thin film with the thickness of 30 nm. The MnAs thin film was epitaxially grown on a GaAs(0 0 1) substrate. The magnetic poles were in one-arranging direction, being independent of the magnetization direction of the film. The poles were pinned at the edges of the rectangular defects until just below the Curie temperature, and formed a stable magnetic-field loop on the MnAs surface. The stability of the magnetic pole pinning shows the distinctive feature of the magnetic domain structure on the surface with a strong anisotropy, which was built in the heterostructure of MnAs and GaAs. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2003.12.024

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We have investigated the electronic and magnetic properties of a MnAs:GaAs granular film with MnAs clusters embedded in the GaAs matrix fabricated by high-temperature annealing of Ga1-xMnxAs using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The XAS line shapes in the Mn 2p core level changed from a localized structure to an itinerant NiAs-type one. Magnetic-field dependence of the XMCD revealed no hysteresis curves at the fixed photon energy where the large XMCD signals were observed, suggesting the superparamagnetic behavior at 100 K. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1637430

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We have investigated magnetic domain structures of MnAs thin films grown on GaAs substrates by a magnetic force microscope. We observed, by an atomic force microscope, rectangular defects along GaAs [110] direction which disperse randomly on the surface of MnAs/GaAs (001). The Curie temperature of MnAs is 45degreesC, and it is successfully confirmed directly by the variable temperature magnetic force microscope observation. We also investigated magnetic domain structures of MnAs/GaAs (111)B, and no apparent relation was observed between the topographic structure and the magnetic domain structure.

DOI： 10.2320/matertrans.44.2578

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In this work, geometric structures for a half-metallic ferromagnet "zinc-blende CrAs", which showed ferromagnetic behavior beyond room temperature, were investigated using fluorescence extended X-ray absorption fine structure (EXAFS) measurement. The EXAFS measurements revealed that As atoms around Cr atoms in the 2 nm CrAs film grown on a GaAs(O 0 1) substrate were coordinated tetrahedrally, indicating formation of zinc-blende CrAs. The Cr-As bond length in the zinc-blende CrAs is 2.49 Angstrom This value is close to that which was estimated from the lattice constant (5.82 Angstrom) of ferromagnetic zinc-blende CrAs calculated by full-potential linearized augmented-plane wave method. The EXAFS analysis show that the theoretically predicted zinc-blende CrAs can be fabricated on GaAs(O 0 1) substrate by low-temperature molecular-beam epitaxy. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(02)01539-2

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In order to realize magnetic nanocrystals for spin electronic devices, we have successfully grown MnAs and/or MnSb nanocrystals on atomically controlled GaAs(001) substrates by molecular beam epitaxy. Surface structures of sulfur- and antimony-terminated GaAs substrates are characterized by synchrotron radiation soft X-ray standing waves. Then, Mn pnictide nanocrystals are grown by super Volmer-Weber epitaxy, taking advantage of low surface energy. MnAs and/or MnSb nanocrystals grown on sulfur-terminated GaAs(001) substrates show ferromagnetic properties with size of 20-30 nm and surface density of more than 10(10) cm(-2). Photoelectron spectroscopy revealed the electronic structures of these magnetic dots. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0368-2048(02)00052-X

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Zinc-blende CrAs/GaAs multilayers were grown by molecular beam epitaxy. It was certified that each CrAs layer maintains an epitaxial relationship with the zinc-blende GaAs structure judging from the reflection high-energy electron diffraction observation. The film contains thicker zinc- blende CrAs layers in total than the CrAs thin film directly grown on the GaAs substrate which has the critical thickness of 3 nm. It was clarified that the optimum thicknesses of CrAs and GaAs to keep a good epitaxial relationship are 2 ML and 2 ML, respectively. The electronic structure of the multilayer is thought to be close to that of the (Ga, Cr)As thin film which has 50% of Cr content judging from x-ray absorption spectroscopy measurements. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1455612

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Ferromagnetic nanoscale zinc-blende MnAs dots were successfully fabricated on a sulfur-passivated GaAs (001) surface by molecular-beam epitaxy. Transmission electron microscopy and selected area electron diffraction showed that the crystalline structure was not the same as that of bulk MnAs with NiAs-type hexagonal crystalline structure, but of zinc-blende type. In in situ photoemission spectroscopy of the zinc-blende MnAs dots, the Fermi edge was not clearly observed and the Mn 3d partial density of states was similar to that of the diluted ferromagnetic semiconductor Ga1-xMnxAs, which also supports the fabrication of zinc-blende MnAs in the nanoscale. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1456396

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A type of GaAs-based ferromagnetic semiconductor, (Ga, Cr)As, was successfully prepared by low-temperature molecular-beam epitaxy. The (Ga, Cr)As thin film shows a flat surface up to the Cr content x=0.18. However, when Cr content x exceeded 0.20, the roughness of the film became larger. The ferromagnetic ordering of the semiconductor sample with the Cr content of x=0.11 was observed. The electronic structures of (Ga, Cr)As were characterized by x-ray absorption spectroscopy (XAS). The XAS spectra show different line shapes in different Cr content. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1455611

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

High resolution angle-resolved photoelectron spectroscopy (ARPES) has been performed on magnetic nanostructures which were in-situ grown hetero-epitaxially on GaAs substrates by low temperature molecular beam epitaxy. Sulfur termination of GaAs surfaces enabled the formation of NiAs-type MnSb dots and zinc-blende (zb) type MnAs dots, showing huge magnetoresistance at RT and half-metallic behavior, respectively. ARPES analysis revealed that the zb-MnAs dots show unique valence band feature with Mn 3d-related peak at about 4 eV of binding energy which is quite similar to (Ga,Mn)As DMS Films. Zb-CrAs thin films on GaAs with T, higher than RT are found to show the band dispersion within 2 eV near the Fermi edge, which is in good agreement with the FLAPW calculation. We have also found that (Ga,Cr)As DMS thin films have the similar valence band features to zb-CrAs.

DOI： 10.1142/S021797920201110X

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In the present work, we report the results of an experimental study of magnetooptical Kerr effect and optical properties in MnAs:GaAs granular films in the spectral range 0.5-4.5 eV at room temperature and at 4.2 K. The possible mechanisms of the giant magnetooptical effect in MnAs:GaAs granular films are discussed on the basis of the obtained results. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(01)01067-8

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We prepared epitaxially grown Fe films on GaAs (0 0 1) surfaces with different reconstructions. The Ga and As concentrations as a function of the Fe thickness were investigated by Auger electron spectroscopy (AES). The Ga atoms hardly segregated, while the AES signal of As still remained at 20 run under a low deposition rate (0.02 nm/s). The segregation was considerably suppressed by the higher deposition rate (0.08 nm/s). The cross-scetional transmission electron microscopy (TEM) image showed that an interface between GaAs and Fe was atomically flat and the surface of the 20 nm Fe film was very flat. We have succeeded in preparing Co/Al2O3/Fe(0 0 1) tunnel junctions based on an Fe(0 0 1) film. The MR ratio was about 9-11 %. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-0248(01)02187-X

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In order to investigate the valence-band discontinuity of the GaAs/AlAs interface, the thickness dependence of the photoemission spectra of a GaAs layer in situ deposited on AlAs by molecular-beam epitaxy has been studied. Although the interface is atomically abrupt, the electronic structure in the interface region displays Al1-xGaxAs alloy-like behaviors. The valence-band maximum as well as the Ga 3d core level show a gradual shift as a function of GaAs layer thickness of less than 2 nm (8 monolayers), which indicates that interface formation needs about 2 nm thickness for the electronic structure of the GaAs layer to become that of bulk GaAs. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1455695

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Epitaxial zinc-blende CrAs thin films were grown at two different temperatures. CrAs (2 nm) grown at 200degreesC formed plateau-shapes, whereas CrAs (2 mn) grown at 300degreesC formed dispersed dots. The thin film grown at 200degreesC showed ferromagnetic behavior at room temperature, and the Curie temperature was estimated to be over 400 K. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(01)00568-6

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The electronic structure of CrAs thin films with nominal thicknesses of 2 nm and 30 nm were studied by angle-resolved photoemission spectroscopy using synchrotron radiation. The CrAs film of 2 nm is expected to form a zinc-blende phase which is predicted to have a half-metallic band structure by theoretical calculation. On the other hand, it is considered that the CrAs film of 30 nm is a polycrystalline compound judging from reflection high-energy electron diffraction patterns. Different valence-band photoemission spectra were obtained for the two films. The photoemission spectra of the CrAs film of 30 nm showed no band dispersion, whereas a band dispersion was observed in that of the CrAs film with the nominal thickness of 2 nm.

DOI： 10.1142/S0218625X02002142

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

New half-metallic ferromagnets have been found in a zinc-blende crystal structure. The zinc-blende CrAs has been designed by <i>ab initio</i> calculations and the calculation predicts the highly spin-polarized electronic band structure. The zinc-blende CrAs thin film has been synthesized on GaAs (001) substrates by molecular-beam epitaxy. The film shows ferromagnetic behavior at room temperature and the magnetic moment per formula unit of CrAs is estimated to be about 3 μ_B, which agrees well with the theoretical prediction. The photoemission spectra of the CrAs film showed the Fermi edges indicating the metallic characteristics and the small band dispersion derived from Cr-3<i>d</i> bands.

DOI： 10.3379/jmsjmag.26.441

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In order to satisfy demands to study the electronic structure of quantum nanostructures, a VUV beamline and a high-resolution and high-throughput photoemission end-station combined with a molecular beam epitaxy (MBE) system have been constructed at the BL-IC of the Photon Factory. An angle-resolved photoemission spectrometer, having high energy- and angular-resolutions; VG Microtech ARUPS10, was installed. The total energy resolution of 31 meV at the 60 eV of photon energy is achieved. For the automated angle-scanning photoemission, the electron spectrometer mounted on a two-axis goniometer can be rotated in vacuum by the computer-cont rolled stepping motors. Another distinctive feature of this end-station is a connection to a MBE chamber in ultahigh vacuum (UHV). In this system, MBE-grown samples can be transferred into the photoemission chamber without breaking UHV. Photoemission spectra of MBE-grown GaAs(001) surfaces were measured with high-resolution and bulk and surface components are clearly resolved. (C) 2001 Elsevier Science B.V, All rights reserved.

DOI： 10.1016/S0168-9002(01)00734-3

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A grazing incidence varied line spacing plane grating monochromator (VLS-PGM) has been designed and installed at the Photon Factory bending magnet beamline, BL-1C. The monochromator is designed to cover 20 to 250eV with a high resolving power as well as a high photon flux and intended for a high-resolution angle-resolved photoemission study of quantum nano-structures. The resolving power of the beamline is observed to be more than 16,000 at around 65 eV and exceeds 10,000 at all the covered energy ranges of the monochromator with photon flux over 10(9) photons/s which shows that this monochromator reaches the expected design goals. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-9002(01)00415-6

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A huge positive magnetoresistance effect, more than 10 000% at room temperature, has been discovered in MnSb granular films. Granular films consisting of nanoscale MnSb dots were fabricated on a sulfur-passivated GaAs (001) substrate by molecular-beam epitaxy, then covered with an Sb thin layer. The MnSb granular films exhibit a strong in-plane anisotropy of the magnetic-field-sensitive current-voltage characteristics. When a constant voltage, above the threshold value, is applied in the [1 1 0] direction of the GaAs (0 0 1) surface, a steep change in the current, which we term magnetoresistive switch (MRS), is driven by the huge magnetoresistance effect under a relatively low magnetic field (less than about 0.2 T). On the other hand, less than 1% magnetoresistance effect was observed when the voltage was applied in thr [1 10] direction of the GaAs surface. The origin of the anisotropy is discussed in terms of the microscopic structural anisotropy at the heterointerface. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(01)00135-7

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Magnetoresistance (MR) effects were investigated on MnSb granular films. These films were composed of GaAs substrates, deposited MnSb dots, and Sb capping layers. With increasing nominal thickness of MnSb, a sudden increase in the magnetic circular dichroism intensity was observed over 0.7 nm. The extra-huge positive MR effect more than 10,000% was observed for the sample with the nominal thickness of 0.2 = at room temperature. I-V curve analysis showed the jump from the high-resistance state to the low-resistance state at the critical voltage. It is considered that the coalescence among dots which occurs at a certain nominal thickness plays an important role in the extra-huge MR effect. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)00619-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

In order to realize a combined system of semiconductor and magnetic nanocrystals fur advanced nanoelectronics, we tried tu heteroepitaxially grow both InGaAs quantum dots on GaAs(001) substrates for laser applications and MnAs and/or MnSb nanocrystals for high-density magnetic recording media by using molecular beam epitaxy. InGaAs and Mn pnictide clots were grown by using modified droplet epitaxy and super Volmer-Weber epitaxy, respectively, taking advantages of self-organization, solid-phase crystallization and low surface energy, respectively. The InGaAs quantum dots exhibited a very sharp PL emission at 946 nm with a full width at half maximum of 21.6 meV, suggesting a drastic improvement in dot size uniformity and crystalline quality over the conventional Stranski-Krastanov dots. On the other hand, the MnAs and/or MnSL nanocrystals grown on sulfur-passivated GaAs(001) substrates show ferromagnetic properties with a size of 16 nm and a surface density of about 10(11) cm(-2).

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

Nano-size MnSb clusters with a nominal thickness of 3 ML were grown on GaAs(111)B substrates by molecular beam epitaxy. The films were capped with GaAs, and the magnetoresistance effect was investigated at room temperature. A large positive magnetoresistance effect of over 50% was observed. The dependency on the sweep rate of magnetic field and an effect of Cr-doping in GaAs capping layers were investigated. The photoinduced MR effect was also observed under laser-irradiation with a photon energy above the band gap of GaAs. It is shown that these phenomena can be attributed to the enhancement of the conductivity by photogenerated carriers.

DOI： 10.3379/jmsjmag.25.502

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We have investigated the electronic structure of MnAs dots on GaAs (100) by photoemission spectroscopy. MnAs dots are grown on the S-passivated GaAs by MBE. The size of the dots is 15 nm. In the valence band photoemission spectra of MnAs dots, the Fermi edge disappears, and there is no spectral intensity at the Fermi level. In the Mn 2p core level spectra of MnAs dots, we have observed a satellite structure which also reflects the 3d electron localization in the MnAs dots. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)02967-1

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We report the fabrication and magnetotransport properties of nanoscaled clusters of manganese antimonide (MnSb) grown on sulfur-passivated GaA(001) substrates by molecular-beam-epitaxy (MBE). The typical diameter and height of dots were about 22 nm and 4 nm, respectively. Uniform dots in size were formed in a self-assembled mode. Magnetotransport properties of MnSb granular films were investigated, and the anisotropic magnetoresistance were observed at room temperature. Large jumps appeared at 9 K in magnetoresistance curves, and the jump structure depends on the sweep rate of the magnetic field. These magnetotransport properties describe well the magnetic behavior of MnSb dots. (C) 2000 American Institute of Physics. [S0021-8979(00)38308-6].

DOI： 10.1063/1.372475

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We show a photoinduced positive magnetoresistance (MR) effect (about 20%) under a low magnetic field (less than 0.1 T) at room temperature. The photoinduced MR effect has been observed in GaAs including nanoscale MnSb islands, when photons with the energy above the band gap of GaAs irradiated the sample. The photoinduced phenomena are due to an enhancement of tunneling probability between MnSb islands by photogenerated carriers in the GaAs matrix. (C) 2000 American Institute of Physics. [S0003-6951(00)02718-2].

DOI： 10.1063/1.126421

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MnSb ultrathin films with the nominal thickness of 0-1.40 nm were grown on sulfur passivated GaAs substrates by molecular beam epitaxy. Atomic force microscopy analysis showed that MnSb formed nanosize clusters on the substrate, and the coalescence of the clusters occurred at the nominal thickness between 0.70 and 1.05 nm. The intensity of the polar magnetic circular dichroism of MnSb clusters suddenly increased when the nominal thickness reached the critical value of 1.05 nm. The coalescence among the dots can be correlated with the sharp increase of the magnetic circular dichroism intensity. (C) 2000 American Institute of Physics. [S0003-6951(00)01013-5].

DOI： 10.1063/1.126153

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We have succeeded in fabricating nanoscale manganese antimonide (MnSb) dots on GaAs substrates by molecular beam epitaxy. Sulfur passivated surfaces were used to decrease the surface energy and to form MnSb dots on the substrate. Morphologies of the dots were investigated by atomic force microscopy, Different growth modes which arose from a difference in growth temperatures were observed, (C) 2000 Elsevier Science B.V, All rights reserved.

DOI： 10.1016/S0022-0248(99)00618-1

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We have investigated the initial growth of MnSb and MnAs films and multilayers on GaAs(1 0 0) and (1 1 1)B substrates by molecular beam epitaxy (MBE) and successfully grown epitaxial MnSb/MnAs multilayers on GaAs(1 1 1)B. We propose a possibility of the novel heat-induced giant magnetoresistance (GMR) effect in the MnSb/MnAs multilayer system. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-0248(99)00619-3

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Ferromagnetic MnAs thin films were grown on clean, S- and Se-passivated GaAs(1 0 0) substrates by molecular beam epitaxy (MBE). Growth modes of MnAs films on GaAs substrates depend on the surface treatment. On the clean and the Se-passivated surfaces MnAs films grow by a layer-by-layer mode, whereas on the S-passivated surface MnAs films grow by an island growth mode, and as a result polycrystalline films are obtained. Photoelectron spectroscopy study revealed that the Se overlayer on the Se-passivated GaAs substrates prevented Ga interdiffusion. We also found that the saturation magnetization of MnAs films on the Se-passivated surface was slightly larger than that on the clean and the S-passivated surfaces. This difference can be explained by the role of Se overlayer in preventing interdiffusion between MnAs and GaAs. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-0248(99)00620-X

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A huge positive magnetoresistance effect has been discovered in MnSb granular films. Granular film consisting of nanoscale MnSb dots that are grown on a sulfur-passivated GaAs (001) substrate by molecular-beam epitaxy, then covered with an Sb thin layer, exhibits magnetic-field-sensitive current-voltage characteristics. When a constant voltage, above the threshold value, is applied to the film, more than 1000% change in the current, which we term magnetoresistive switch, is driven by the magnetoresistance effect under a relatively low magnetic field (less than 0.5 T) at room temperature. (C) 2000 American Institute of Physics. [S0003-6951(00)04303-5].

DOI： 10.1063/1.125753

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

A huge positive magnetoresistance effect in a relatively low magnetic field (less than 0.5 T) at room temperature was discovered in MnSb granular films. A granular film consisting of nano-scale MnSb clusters was grown on a sulfur-passivated GaAs(001) substrate by molecular beam epitaxy, then covered with an Sb thin layer. The granular film shows magnetic-field-sensitive current-voltage characteristics. When a constant voltage, above the threshold value, is applied to the film, a more than 1000 percent change in the current, which we term a <i>magnetoresistive switch</i>, is driven by the magnetoresistance effect. A possible mechanism for the magnetoresistive switch effect is discussed.

DOI： 10.3379/jmsjmag.24.451

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

MnSb ultra-thin films with nominal thicknesses of 0.35, 0.70, 1.05, and 1.40 nm were grown on sulfur-passivated GaAs (001) substrates by molecular beam epitaxy. Atomic force microscopy analyses showed that MnSb formed nanosized dots on the substrate, and that coalescence of the clusters occurred at nominal thicknesses between 0.70 and 1.05 nm. The intensity of the polar magnetic circular dichroism of MnSb clusters and the saturation magnetization suddenly increased when the nominal thickness reached the critical value of 1.05 nm. The coalescence of the dots can be correlated with the sharp increase in the MCD intensity.

DOI： 10.3379/jmsjmag.24.499

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

High quality nickel films were electrodeposited directly onto n-GaAs using galvanostatic control. It was seen that by varying the current density the crystallographic orientation of the films could be controlled. For a current density of 15 mA/cm(2), a highly dominant (220) crystallographic orientation was obtained, Magnetic measurements revealed a strong uniaxial anisotropy in these films, Moreover, Kerr spectroscopy measurements (1.4 to 4.5 eV) showed an enhanced Kerr rotation of -0.17 degrees at 3.2 eV, which may be attributed to the strong magnetic anisotropy and the exceptional crystal quality of the films.

DOI： 10.1109/20.801055

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

We have successfully grown manganese pnictides epitaxial multilayers [MnSb/MnAs]5 on GaAs by molecular beam epitaxy. The structural and magnetic properties of the multilayers have been investigated by reflection high energy electron diffraction, X-ray diffraction, and superconducting quantum interference device.

DOI： 10.3379/jmsjmag.23.688

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

We have carried out the magnetic circular dichroism (MCD) measurements in the VUV region near M-2,M-3 absorption edges of Cu and Co for Cu/Co multilayers in order to investigate the perpendicular magnetization of the system. Circularly polarized SR light was incident almost normal to the sample surface and the reflected light was detected, corresponding to the information about perpendicular magnetic moments. The MCD spectrum of the magnetic layers at Co M-2,M-3 edges showed one negative peak. Although Cu is non-magnetic, a similar MCD profile was obtained for Cu M-2,M-3 edges. These results indicate that the perpendicular magnetic moments of non-magnetic Cu are induced near the Cu/Co interfaces of multilayers and the directions of the magnetic moments in Cu and Co layers are parallel with each other along the direction of applied magnetic field.

DOI： 10.7567/JJAPS.38S1.419

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We have grown ferromagnetic MnAs thin films on S- and Se-passivated GaAs substrates by molecular beam epitaxy (MBE). Growth modes of MnAs films on GaAs(100) substrates were changed by the surface treatment. We found that on the clean and the Se-passivated surfaces, MnAs films grow by a layer-by-layer mode. In contrast, on the S-passivated surface MnAs grows by an island growth mode. and polycrystalline films are obtained. We also found that the magnetization of the MnAs film on Se-passivated surface is larger than that on clean and S-passivated surfaces

DOI： 10.3379/jmsjmag.23.694

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Magnetics Society of Japan  

We report the formation of nanosize ferromagnetic MnAs dots on S-passivated GaAs by molecular beam epitaxy. The structural and magnetic properties of the dots have been characterized by high resolution scanning electron microscopy, and superconducting quantum interference device magnetometer. The average size and the density of these MnAs dots were 16.3nm and 2.3×10¹⁰/cm³ respectively. These dots show ferromagnetism at low temperature and the Curie temperature is lower than the bulk value.

DOI： 10.3379/jmsjmag.23.691

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

We first report the formation and magnetic properties of MnAs and MnSb nanocrystals by "super Volmer-Weber epitaxy" utilizing very low surface energy substrates such as sulfur-passivated GaAs substrates. On the S-passivated GaAs surface MnAs dots with the size of about 16 nm and the density of 2x10(10) cm(-2) were successfully grown. SQUID analysis of these dots showed partly vertical easy magnetization axis. However, on the Se-GaAs surface, no MnAs dots were grown. SRPES revealed that Se atoms were segregated to the MnAs surface, probably playing a role of surfactant for the layer growth mode.

DOI： 10.7567/JJAPS.38S1.373

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Recently half-metallic ferromagnetic materials have attracted great attentions due to the possibility of applications to 'spintronic' devices. In this contribution, an epitaxial growth of zinc-blende type CrAs film which is predicted by theoretical calculations to possess a half-metallic band structure is reported. The CrAs thin film shows a ferromagnetic behavior at room temperature. Fabrication of a superlattice including zinc-blende CrAs and GaAs is also reported.

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