Kohei Ueda

Spin Hall magnetoresistance (SMR) is an intriguing spin-dependent transport phenomenon in bilayers consisting of non-magnetic and magnetic layers. Here, we report on the influence of longitudinal spin current absorption by the magnetic layer on SMR in bilayers composed of Co₂₀Fe₆₀B₂₀ (CoFeB) and epitaxial SrIrO₃, where SrIrO₃ is used as a highly resistive spin current source. We observed a clear SMR signal and an enhancement in the SMR ratio with increasing CoFeB layer thickness, in qualitative agreement with an SMR model that incorporates the spin current absorption. The effective spin Hall angle is corrected from 0.07 to 0.12 with consideration of the spin current absorption, corresponding to a relative correction of ∼71%. Our findings highlight the pronounced impact of the spin current absorption by the magnetic layer on the SMR mechanism when employing highly resistive non-magnetic layer such as SrIrO₃, as well as other emerging quantum materials.

Spin Hall magnetoresistance (SMR) is an intriguing spin-dependent transport phenomenon in bilayers consisting of non-magnetic and magnetic layers. Here, we report on the influence of longitudinal spin current absorption by the magnetic layer on SMR in bilayers composed of Co$_{20}$Fe$_{60}$B$_{20}$ (CoFeB) and epitaxial SrIrO$_{3}$, where SrIrO$_{3}$ is used as a highly-resistive spin current source. We observed a clear SMR signal and an enhancement in the SMR ratio with increasing CoFeB layer thickness, in qualitative agreement with an SMR model that incorporates the spin current absorption. The effective spin Hall angle is corrected from 0.07 to 0.12 with consideration of the spin current absorption, corresponding to a relative correction of ~71%. Our findings highlight the pronounced impact of the spin current absorption by the magnetic layer on the SMR mechanism when employing highly-resistive non-magnetic layer such as SrIrO$_{3}$, as well as other emerging quantum materials.

Transition metal oxides are a platform for exploring strain-engineered intriguing physical properties and developing spintronic or flexible electronic functionalities owing to the strong coupling of spin, charge, and lattice degrees of freedom. In this study, we exemplify the strain-engineered magnetism of La2/3Sr1/3MnO3 in freestanding and rippled membrane forms without and with process-induced strain, respectively, prepared by the epitaxial lift-off technique. We find that the deposition of the Pt/Ti stressor suppresses the crack formation in the lift-off process and induces a ripple structure in the La2/3Sr1/3MnO3 membrane. Laser micrograph and Raman spectroscopy show a ripple period of about 30 μm and a height of a few μm, where alternating convex and concave structures are subjected to a tensile strain of 0.6% and a compressive strain of 0.5%, respectively. While the freestanding La2/3Sr1/3MnO3 membrane exhibits room-temperature ferromagnetism, the macroscopic magnetic transition temperature (TC) of the rippled membrane is reduced by as much as 27%. Temperature-variable Kerr microscopy observation in the rippled membrane reveals that the spatial variation of TC is ∼4% of the macroscopic TC, which coincides with the local strains at convex and concave structures. The large reduction of macroscopic TC in the rippled membrane may be ascribed to the lattice disorders due to the strain gradient. Our demonstration of tuning ferromagnetism by the ripple structure validates the high potential of the process-induced strain in the epitaxial lift-off technique and paves the way for strain-mediated emerging physical properties in various transition metal oxides.

An antiferromagnetic metal with a two-dimensional triangular network offers a unique playground of intriguing magneto-transport properties and functionalities stemming from the interplay between conducting electrons and intricate magnetic phases. A NiAs-type CrSe is one of the candidates owing to alternate stackings of Cr and Se triangular atomic networks in its crystal structure. While the fabrication of CrSe thin films is indispensable to develop functional devices, studies on its thin-film properties have been limited to date due to the lack of metallic samples. Here, we report on the realization of metallic conductivities of CrSe thin films, which allows us to investigate their intrinsic magneto-transport properties. The metallic sample exhibits a co-occurrence of weak ferromagnetism with perpendicular magnetic anisotropy and antiferromagnetic behavior, indicating the presence of non-coplanar spin structures. In addition, control of the polarity and tilting angle of the non-coplanar spin structure is accomplished by a sign of cooling magnetic fields. The observed non-coplanar spin structure, which can be a source of emergent magnetic field acting on the conducting electrons, highlights the high potential of the triangular lattice antiferromagnet and provides a unique platform for functional thin-film devices composed of NiAs-type derivative Cr chalcogenides and pnictides.

We report on spin Hall magnetoresistance (SMR) in bilayers composed of Pt and magnetic insulator MgFe$_{2}$O$_{4}$ (MFO) with spinel structure. The Pt thickness dependence of the SMR reveals that annealing of the MFO surface before depositing the Pt layer is crucial for a large SMR with better interface quality. We also found that oxygen pressure during the MFO growth hardly affects the SMR while it influences on magnetic property of the MFO film. Our findings provide important clues to further understanding the spin transport at interfaces containing magnetic insulators, facilitating development of low power consumption devices.

We report on spin Hall magnetoresistance (SMR) in bilayers composed of Pt and magnetic insulator MgFe₂O₄ (MFO) with spinel structure. The Pt thickness dependence of the SMR reveals that annealing of the MFO surface before depositing the Pt layer is crucial for a large SMR with better interface quality. We also found that oxygen pressure during the MFO growth hardly affects the SMR, while it influences the magnetic property of the MFO film. Our findings provide important clues to further understanding the spin transport at interfaces containing magnetic insulators, facilitating development of low power consumption devices.

Manganite perovskites host emerging physical properties of strongly-correlated electrons with charge, spin, and lattice degrees of freedom. Using the epitaxial lift-off technique, we report enhancement of saturation magnetization and the ferromagnetic transition temperature of freestanding La_2/3Sr_1/3MnO₃ membrane compared with as-grown film on SrTiO₃ substrate involving lateral tensile strain. Structural analysis reveals shrinkage of unit-cell volume by tensile strain relaxation in the freestanding membrane, which causes enhancement of the ferromagnetic interaction. The impact of the microscopic lattice deformation on the ferromagnetism of La_2/3Sr_1/3MnO₃ indicates a high potential of this material for flexible electronics applications with intriguing functionalities in strongly-correlated electron systems.