1212.1964 (Ran Cheng et al.)

Microscopic Theory of Spin Transfer Torques in Ferromagnets    [PDF]

Ran Cheng, Qian Niu

Spin transfer torque (STT), involving both adiabatic and non-adiabatic contributions, provides key mechanisms to current-induced phenomena in ferromagnets. While the adiabatic STT has been well studied, current understanding of the non-adiabatic STT is based on macroscopic models. By computing microscopically the response of conduction electron spins to a time varying and spatially inhomogeneous magnetic background, we derive the adiabatic and non-adiabatic STT in a unified fashion. Our result justifies the macroscopic theory (Phys. Rev. Lett. 93, 127204 (2004)) and clarifies the physical origin of every coefficient. We also provide a benchmark on the validity of the theory and explain why a recent experiment shows deviation.

View original: http://arxiv.org/abs/1212.1964