Unified description of bulk and interface-enhanced spin pumping

TL;DR

This paper presents a unified diffusive model for spin pumping, showing how interface effects can dramatically enhance spin accumulation up to a universal limit, with implications for optimizing spintronic devices.

Contribution

It introduces a comprehensive diffusive framework that describes both bulk and interface-enhanced spin pumping, extending previous theories and identifying conditions for maximum spin accumulation.

Findings

Spin accumulation is proportional to hbar omega in uniform systems.

Interface effects can enhance spin accumulation to a universal value of hbar omega.

Optimal system dimensions are on the order of sqrt(2pi D omega).

Abstract

The dynamics of non-equilibrium spin accumulation generated in metals or semiconductors by rf magnetic field pumping is treated within a diffusive picture. The dc spin accumulation produced in a uniform system by a rotating applied magnetic field or by a precessing magnetization of a weak ferromagnet is in general given by a (small) fraction of hbar omega, where omega is the rotation or precession frequency. With the addition of a neighboring, field-free region and allowing for the diffusion of spins, the spin accumulation is dramatically enhanced at the interface, saturating at the universal value hbar omega in the limit of long spin relaxation time. This effect can be maximized when the system dimensions are of the order of sqrt(2pi D omega), where D is the diffusion constant. We compare our results to the interface spin pumping theory of A. Brataas et al. [Phys. Rev. B 66, 060404(R) (2002)].