Theory of Kondo suppression of spin polarization in nonlocal spin valves

TL;DR

This paper presents a theoretical model showing how the Kondo effect suppresses spin polarization and diffusion length in nonlocal spin valves, explaining experimental discrepancies and providing explicit suppression expressions.

Contribution

It introduces a modified spin drift-diffusion model incorporating Kondo physics, revealing its impact on spin transport properties in all-metal nonlocal spin valves.

Findings

Kondo physics significantly reduces spin diffusion length.

Explicit expression for spin polarization suppression due to Kondo effect.

Estimated Elliot-Yafet probability for Kondo spin flip scattering is 0.7 ± 0.4.

Abstract

We theoretically analyze contributions from the Kondo effect to the spin polarization and spin diffusion length in all-metal nonlocal spin valves. Interdiffusion of ferromagnetic atoms into the normal metal layer creates a region in which Kondo physics plays a significant role, giving discrepancies between experiment and existing theory. We start from a simple model and construct a modified spin drift-diffusion equation which clearly demonstrates how the Kondo physics not only suppresses the electrical conductivity but even more strongly reduces the spin diffusion length. We also present an explicit expression for the suppression of spin polarization due to Kondo physics in an illustrative regime. We compare this theory to previous experimental data to extract an estimate of the Elliot-Yafet probability for Kondo spin flip scattering of 0.7 $\pm$ 0.4, in good agreement with the value of 2/3 derived in the original theory of Kondo.