Using microscopic theory, we investigate the properties of a spin current driven by magnetization dynamics. In the limit of smooth magnetization texture, the dominant spin current induced by the spin pumping effect is shown to be the diffusive spin current, i.e., the one arising from only a diffusion associated with spin accumulation. That is to say, there is no effective field that locally drives the spin current. We also investigate the conversion mechanism of the pumped spin current into a charge current by spin-orbit interactions, specifically the inverse spin Hall effect. We show that the spin-charge conversion does not always occur and that it depends strongly on the type of spin-orbit interaction. In a Rashba spin-orbit system, the local part of the charge current is proportional to the spin relaxation torque, and the local spin current, which does not arise from the spin accumulation, does not play any role in the conversion. In contrast, the diffusive spin current contributes to the diffusive charge current. Alternatively, for spin-orbit interactions arising from random impurities, the local charge current is proportional to the local spin current that constitutes only a small fraction of the total spin current. Clearly, the dominant spin current (diffusive spin current) is not converted into a charge current. Therefore, the nature of the spin current is fundamentally different depending on its origin and thus the spin transport and the spin-charge conversion behavior need to be discussed together along with spin current generation

Spin transport driven by the temperature gradient in ferromagnetic metals is studied based on a microscopic theory. It is shown that the temperature gradient works as an effective field equivalent to the electric field as for both the spin current generation and the spin relaxation torque. The thermally driven contribution of the spin current and the relaxation torque are thus proportional to ∇T and ∇ 2 T , respectively.

Spin transport driven by an external electric field in uniform metallic ferromagnets with the spin-orbit interaction arising from random impurities is studied microscopically. Spin relaxation torque T is shown to be written by spatial derivatives of the electric field, but with anisotropy arising from the magnetization. The field-driven contribution of the spin current is also anisotropic.The diffusive spin current is shown to be written as a gradient of the spin chemical potential, and the linear-response expression for the spin chemical potential is derived. It is discussed that the β term in the spin transfer torque can also be anisotropic.

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We present gauge-invariant theory of the dynamic inverse spin Hall effect driven by the spin-orbit interaction in metallic systems. Charge conservation is imposed diagrammatically by including vertex corrections. We show the charge current is induced by an effective electric field that is proportional to the spin current pumped by the magnetization dynamics. The result is consistent with recent experiments.