Speaker
Description
We argue that the usual magnetization $\vec{M}$, which represents a correlated property of 10$^{23}$ variables, but is summarized by a single variable, cannot diffuse; only the non-equilibrium spin accumulation magnetization $\vec{m}$, due to excitations, can diffuse. For transverse deviations from equilibrium this is consistent with work by Silsbee, Janossy, and Monod (1979), and by Zhang, Levy, and Fert (2002).
We examine the corresponding theory of longitudinal deviations for a ferromagnet using $M$ and the longitudinal spin accumulation $m$. If an initial longitudinal magnetic field $H$ has a frozen wave component that is suddenly removed, the system approaches equilibrium via two exponentially decaying coupled modes of $M$ and $m$, one of which includes diffusion. If the system in a slab geometry is subject to a time-oscillating spin current, the system approaches equilibrium via two spatially decaying modes, one associated with spacial decay away from each surface. We also explore the possibility that decay of $M$ directly to the lattice is negligible, so that decay of $M$ must be mediated through decay to $m$ and then to the lattice.
