Seminar über Theoretische Festkörperphysik
Dr. Mikhail Titov
Room 10.01, 10th Floor, Bldg. 30.23, KIT Campus South
Radboud University Nijmegen, the Netherlands
Dr. Igor Gornyi, Dr. Boris Narozhny
Spin-orbit and spin-transfer torques are competing forces that drive magnetic domains in the heavy-metal/ferromagnet bi-layers in the presence of electric current. In this talk I present a microscopic theory of both effects that is obtained from generalised Kubo formalism for a disordered electron system and completely avoids the notion of spin currents and spin Hall effect. I also treat the Gilbert damping on the same footing. In this formalism the torques are naturally related to susceptibility tensors that can be evaluated microscopically for any given model. In this talk I mainly focus on the torques arising in heavy-metal/ferromagnet bilayers and demonstrate that spin-orbit interactions are generally responsible for a giant enhancement of spin transfer toques. I show that as the result of spin-orbit coupling the so-called beta torque is naturally decoupled to the in-plane and out-of-plane components that become different by several orders of magnitude.
The same behaviour is characteristic for the Gilbert damping. Finally I discuss theory applications for spin torques arising in heterostructures involving topological insulators.