Description:

Title: Dynamics of Magnets: not Landau-Lifshitz vs Bloch, but Landau-Lifshitz AND Bloch

Speaker: Prof. Wayne Saslow, Texas AM University

Abstract: It is well-known that magnets have an equilibrium magnetization M, whose tipping is described by Landau and Lifshitz's 1935 dynamics. In recent years it has been realized that out-of-equilibrium magnets have a ``spin accumulation'' m whose properties have not been fully described. Using spin-dependent Fermi Liquid theory we show that m satisfies a Bloch equation including diffusion. At surfaces M satisfies boundary conditions from micromagnetics, whereas m satisfies spin flux conditions from irreversible thermodynamics. We apply these ideas to spin-pumping (of magnetization from a ferromagnet to a normal metal) and to spin transfer torque (angular momentum from a spin-polarized current in a normal metal to a ferromagnet). The largely forgotten 1979 model of Silsbee, Janossy, and Monod is thereby justified. For spin-pumping the source term is frequency-independent, whereas in the current "paradigm" theory the source term is linear in frequency.

Keywords: Physics, Astronomy, CMP