Abstract:
Electric currents can be used to control magnetization in thin-film magnets, offering a route toward faster and more energy-efficient magnetic devices, such as nonvolatile magnetic random-access memory (MRAM). One approach to such control is to harness spin-orbit coupling, which enables angular momentum transfer between the crystal lattice and the magnetization via conduction electrons. The resulting current-induced spin-orbit torque can generate effective forces that reorient magnetic moments. I will describe first-principles calculations of spin transport and current-driven torques in realistic layered materials, including the effects of atomic-scale disorder. In particular, I will discuss how reduced symmetry can produce torque components with unusual directions that are useful for switching magnets whose preferred orientation is perpendicular to the film plane. I will present an example of such torques in ferromagnet/nonmagnet/ferromagnet trilayers. I will also discuss the recently proposed spin-splitter effect, which can enable spin torques in a two-layer device without relying on spin-orbit coupling. This effect requires a magnetic source of spin current, such as an altermagnet or a crystallographically anisotropic ferromagnet.