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k-asymmetric spin splitting at the interface between transition metal ferromagnets and heavy metals
Grytsyuk, Sergiy,Belabbes, Abderrezak,Haney, Paul M.,Lee, Hyun-Woo,Lee, Kyung-Jin,Stiles, M. D.,Schwingenschlö,gl, Udo,Manchon, Aurelien American Physical Society 2016 Physical Review B Vol.93 No.17
<P>We systematically investigate the spin-orbit coupling-induced band splitting originating from inversion symmetry breaking at the interface between a Co monolayer and 4d (Tc, Ru, Rh, Pd, and Ag) or 5d (Re, Os, Ir, Pt, and Au) transition metals. In spite of the complex band structure of these systems, the odd-in-k spin splitting of the bands displays striking similarities with the much simpler Rashba spin-orbit coupling picture. We establish a clear connection between the overall strength of the odd-in-k spin splitting of the bands and the charge transfer between the d orbitals at the interface. Furthermore, we show that the spin splitting of the Fermi surface scales with the induced orbital moment, weighted by the spin-orbit coupling.</P>
Spin-orbit torques from interfacial spin-orbit coupling for various interfaces
Kim, Kyoung-Whan,Lee, Kyung-Jin,Sinova, Jairo,Lee, Hyun-Woo,Stiles, M. D. American Physical Society 2017 Physical review. B Vol.96 No.10
<P>We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal-metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a damping like component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism.</P>
Synthetic antiferromagnetic spintronics
Duine, R. A.,Lee, Kyung-Jin,Parkin, Stuart S. P.,Stiles, M. D. Nature Publishing Group UK 2018 NATURE PHYSICS Vol.14 No.3
<P>Spintronic and nanomagnetic devices often derive their functionality from layers of different materials and the interfaces between them. We discuss the opportunities that arise from synthetic antiferromagnets consisting of two or more ferromagnetic layers that are separated by metallic spacers or tunnel barriers and have antiparallel magnetizations.</P>
Perpendicular magnetic anisotropy of two-dimensional Rashba ferromagnets
Kim, Kyoung-Whan,Lee, Kyung-Jin,Lee, Hyun-Woo,Stiles, M. D. American Physical Society 2016 Physical Review B Vol.94 No.18
<P>We compute the magnetocrystalline anisotropy energy within two-dimensional Rashba models. For a ferromagnetic free-electron Rashba model, the magnetic anisotropy is exactly zero regardless of the strength of the Rashba coupling, unless only the lowest band is occupied. For this latter case, the model predicts in-plane anisotropy. For a more realistic Rashba model with finite band width, the magnetic anisotropy evolves from in-plane to perpendicular and back to in-plane as bands are progressively filled. This evolution agrees with first-principles calculations on the interfacial anisotropy, suggesting that the Rashba model captures energetics leading to anisotropy originating from the interface provided that the model takes account of the finite Brillouin zone. The results show that the electron density modulation by doping or an external voltage is more important for voltage-controlled magnetic anisotropy than the modulation of the Rashba parameter.</P>
Spin currents and spin–orbit torques in ferromagnetic trilayers
Baek, Seung-heon C.,Amin, Vivek P.,Oh, Young-Wan,Go, Gyungchoon,Lee, Seung-Jae,Lee, Geun-Hee,Kim, Kab-Jin,Stiles, M. D.,Park, Byong-Guk,Lee, Kyung-Jin Nature Publishing Group 2018 NATURE MATERIALS Vol.17 No.6
<P>Magnetic torques generated through spin-orbit coupling(1-8) promise energy-efficient spintronic devices. For applications, it is important that these torques switch films with perpendicular magnetizations without an external magnetic field(9-14). One suggested approach(15) to enable such switching uses magnetic trilayers in which the torque on the top magnetic layer can be manipulated by changing the magnetization of the bottom layer. Spin currents generated in the bottom magnetic layer or its interfaces transit the spacer layer and exert a torque on the top magnetization. Here we demonstrate field-free switching in such structures and show that its dependence on the bottom-layer magnetization is not consistent with the anticipated bulk effects(15). We describe a mechanism for spin-current generation(16,17) at the interface between the bottom layer and the spacer layer, which gives torques that are consistent with the measured magnetization dependence. This other-layer-generated spin-orbit torque is relevant to energy-efficient control of spintronic devices.</P>