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

In this study, we investigated the nonlinear response of hybrid magnons consisting of acoustic and optic magnon modes in in-plane magnetized synthetic antiferromagnets. Using the heterodyne magneto-optical Kerr effect technique, we optically measured the properties of hybrid magnons under various excitation powers. These measurements revealed that the increase in the excitation power changed the resonance spectrum and the intensity distribution of the magnon dispersion relation due to the nonlinear dynamics of propagating magnons. This study advances the understanding of the nonlinear behavior of hybrid magnons, contributing to the future development of magnonic logic circuits and quantum devices.

DOI： 10.1063/5.0251351

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

DOI： 10.3379/msjmag.2501r004

Open Access

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

DOI： 10.3379/msjmag.2501r003

Open Access

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

DOI： 10.1038/s41467-024-54125-0

Open Access

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

Altermagnets have spin-split band structures that correspond to the rotational symmetry of the two sublattices in real space. Theoretically, their unique band structures are expected to exhibit intriguing transport phenomena, depending on their magnetic structures. Anomalous Hall effect (AHE) measurement is a method by which to electrically detect magnetic structure and has been reported for typical altermagnets, such as RuO2 and MnTe. However, AHE measurements are limited to specific cases. Thus, it is important to apply other methods by which to determine functionality based on magnetic structure. In this study, we report the spin Hall magnetoresistance (SMR) in a RuO2 (1 nm)/Pt (10 nm) system. A negative SMR signal is clearly observed, indicating the spin-flop antiferromagnetic structure of RuO2. Interestingly, a negative SMR was observed, even at 1 T, which is much smaller than the estimated spin-flop field reported in a previous study. This reflects the thinner film of RuO2 in our study, suggesting that thickness control is effective in adjusting the magnetic anisotropy of RuO2. In addition, the temperature-dependent SMR measurement revealed the Néel temperature of 1 nm thick RuO2 to be 70 ± 9 K. Our results show that SMR measurement can serve as an efficient tool to explore the magnetic features in an altermagnet.

DOI： 10.1063/5.0213320

Open Access

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

DOI： 10.3379/msjmag.2411r003

Open Access

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

The critical current in a superconductor (SC) determines the performance of many SC devices, including SC diodes which have attracted recent attention. Hitherto, studies of SC diodes are limited in the DC-field measurements, and their performance under a high-frequency current remains unexplored. Here, we conduct the first investigation on the interaction between the DC and terahertz (THz) current in a SC artificial superlattice. We found that the DC critical current is sensitively modified by THz pulse excitations in a nontrivial manner. In particular, at low-frequency THz excitations below the SC gap, the critical current becomes sensitive to the THz-field polarization direction. Furthermore, we observed anomalous behavior in which a supercurrent flows with an amplitude larger than the modified critical current. Assuming that vortex depinning determines the critical current, we show that the THz-current-driven vortex dynamics reproduce the observed behavior. While the delicate nonreciprocity in the critical current is obscured by the THz pulse excitations, the interplay between the DC and THz current causes a non-monotonic SC/normal-state switching with current amplitude, which can pave a pathway to developing SC devices with novel functionalities.

DOI： 10.1038/s41467-024-48738-8

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Other Link： https://www.nature.com/articles/s41467-024-48738-8

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.11470/jsaprev.240206

Open Access

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Abstract

The superconducting diode effect (SDE), which causes a superconducting state in one direction and a normal‐conducting state in another, has significant potential for developing ultralow power consumption circuits and non‐volatile memory. However, the practical control of the SDE necessities the precise tuning of current, temperature, magnetic field, or magnetism. Therefore, the mechanisms of the SDE must be understood to develop novel materials and devices capable of realizing the SDE under more controlled and robust conditions. This study demonstrates an intrinsic zero‐field SDE with an efficiency of up to 40% in Fe/Pt‐inserted non‐centrosymmetric Nb/V/Ta superconducting artificial superlattices. The polarity and magnitude of the zero‐field SDE are controllable by the direction of magnetization, indicating that the effective exchange field acts on Cooper pairs. Furthermore, the first‐principles calculation indicates that the SDE can be enhanced by an asymmetric configuration of proximity induced magnetic moments in superconducting layers, which induces a magnetic toroidal moment. This study has important implications regarding the development of novel materials and devices that can effectively control the SDE. Moreover, the magnetization control of the SDE is expected to aid in the designing of superconducting quantum devices and establishing a material platform for topological superconductors.

DOI： 10.1002/adma.202304083

PubMed

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

DOI： 10.3379/msjmag.2309r001

Open Access

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

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

DOI： 10.1063/5.0144602

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

Abstract

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

DOI： 10.35848/1882-0786/ac99b9

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Other Link： https://iopscience.iop.org/article/10.35848/1882-0786/ac99b9/pdf

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

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

DOI： 10.1038/s41565-022-01159-4

PubMed

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Other Link： https://www.nature.com/articles/s41565-022-01159-4

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

DOI： 10.35848/1347-4065/abfdc1

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Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/abfdc1/pdf

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

DOI： 10.35848/1882-0786/ac03c0

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5126615

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5000815

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.94.094433

Event date： 2025.3

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