Microscopic Calculation of Spin Torques and Forces

Spin torques, that is, effects of conduction electrons on magnetization dynamics, are calculated microscopically in the first order in spatial gradient and time derivative of magnetization. Special attention is paid to the so-called \beta-term and the Gilbert damping, \alpha, in the presence of electrons' spin-relaxation processes, which are modeled by quenched magnetic impurities. Two types of forces that the electric/spin current exerts on magnetization are identified based on a general formula relating the force to the torque.Comment: Proceedings of ICM2006 (Kyoto), to appear in J. Mag. Mag. Ma

Electronic pressure on ferromagnetic domain wall

The scattering of the eletron by a domain wall in a nano-wire is studied perturbatively to the lowest order. The correction to the thermodaynamic potential of the electron system due to the scattering is calculated from the phase shift. The wall profile is determined by taking account of this correction, and the result indicates that the wall in a ferromagnet with small exchange coupling can be squeezed to be very thin to lower the electron energy

Effect of Spin Current on Uniform Ferromagnetism: Domain Nucleation

Large spin current applied to a uniform ferromagnet leads to a spin-wave instability as pointed out recently. In this paper, it is shown that such spin-wave instability is absent in a state containing a domain wall, which indicates that nucleation of magnetic domains occurs above a certain critical spin current. This scenario is supported also by an explicit energy comparison of the two states under spin current.Comment: 4 pages, 1 figure, REVTeX, rivised version, to appear in Physical Review Letter