We have made good progress in developing an AC magnetoeletronic circuit theory. Our main breaktrough this year was the developing of a novel spin-pumping concept, published in Phys. Rev. Lett. 88, 117601 (2002).

The precession of the magnetization of a ferromagnet is shown to transfer spins into adjacent normal metal layers. This pumping of spins slows down the precession corresponding to an enhanced Gilbert damping constant in the Landau-Lifshitz equation when the adjacent normal metal is a good spin sink. The damping is expressed in terms of the scattering matrix of the ferromagnetic layer, which is accessible to model and first-principles calculations. Our estimates for permalloy thin films explain the trends observed in recent experiments.

The spin-pumping mechanism can also be used to create a spin-battery, as we proposed in Phys. Rev. B 66, 060404 (R) (2002). Precessing ferromagnets are predicted to inject a spin current into adjacent conductors via conductance mismatch with, for example, doped semiconductors. This opens the way to create a pure spin source (spin battery) by the ferromagnetic resonance.  We estimate the spin current and spin bias for different material combinations.

We have thus accomplished the development of a framework to understand time-dependent transport in hybrid ferromagnet-normal metal systems. In the coming year(s), this concept will be used to understand novel hybrid systems, experimental situations and for further progress in the theory of AC magnetotransport.