Theoretical study on plea-rival and optical manipulation of magoetization

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(1) The equation of motion of a domain wall under current was derived and analyzed. By taking account of two driving mechanisms (spin transfer and momenturn tinsfer), intrinsic pinning (magnetic anisotropy) and extrinsic pinning (sample inhomogeneity), the depinning mechanisms are classified. The threshold current and domain-wall velocity are obtained for each case, and experimental results are discussed therewith(1) The equation of motion of a domain wall under current was derived and analyzed. By taking account of two driving mechardems (spin transfer and momenturn tinsfer), intrinsic pinning (magnetic anisotropy) and extrinsic pinning (sample inhomogeneity), the depinning mechanisms are classified The threshold current and domain-wall velocity are obtained for each case, and experimental results am discussed therewith(2) Various spin torques that the currents exert on magnetization was microscopically calculated for general magnetization texture. Two theoretical frameworks have been … More developed that can treat electrons' spin-relaxation processes. They are "small-amplitude method", which offers a reliable treatment of non-equilibrium states but is restricted to small-amplitude dynamics, and "gauge-field method", which can treat finite-amplitude dynamics. Simple-minded application of the latter method failed to reproduce the damping but we could overcome this difficulty by a careful treatment of spin-relaxation proceeses. A new physical picture of the damping was obtained as a by-product.(3) Current-driven motion of a magnetic vortex, typically formed in a magnetic disk, was studied theoretically. Resonant excitation of the core, and the reversal of the core magnetization were studied/found by simulations (Prof. Nakatani, UEC) and confirmed experimentally (by Ono group, Kyoto University).(4) Spin-polarized. current in a ferromagnet was known to lead to the softening of spin waves, and eventually to the instability of the uniformly magnetized state. We have found that this instability is followed by the formation of magnetic domain walls (in thin wires) or magnetic vortices (in films or wide wires). The dynamics of two interacting vortices under current was classified according to their vorticity, and polarity which explains well the essential features of the simulation results. Less