We present a consistent microscopic study of spin pumping effects for both metallic and insulating ferromagnets. As for the metallic case, we present a simple quantum mechanical picture of the effect as due to the electron spin flip as a result of a nonadiabatic (off-diagonal) spin gauge field. The effect of interface spin-orbit interaction is briefly discussed. We also carry out a field-theoretic calculation to discuss on equal footing the spin current generation and torque effects such as an enhanced Gilbert damping constant and a shift of precession frequency both in metallic and insulating cases. For thick ferromagnetic metals, our study reproduces the results of previous theories such as the correspondence between the dc component of the spin current and the enhancement of the damping. For thin metals and insulators, the relation turns out to be modified. For the insulating case, driven locally by interface sd exchange interaction due to magnetic proximity effect, the physical mechanism is distinct from the metallic case. Further study of the proximity effect and interface spin-orbit interaction would be crucial to interpret experimental results in particular for insulators.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics