Magnetization reversal driven by spin-injection : a mesoscopic spin-transfer effect

TL;DR

This paper develops a mesoscopic model of spin-transfer effects driven by spin-injection at ferromagnetic junctions, modifying magnetization dynamics and predicting activation and fluctuation behaviors consistent with experiments.

Contribution

It introduces a thermokinetic framework incorporating spin-injection into magnetization dynamics, extending the Landau-Lifshitz-Gilbert equation with new diffusion terms.

Findings

Derived expressions for effective energy barrier and critical current.

Predicted modifications to magnetic fluctuations due to spin-injection.

Results align with experimental measurements of spin-transfer effects.

Abstract

A mesoscopic description of spin-transfer effect is proposed, based on the spin-injection mechanism occurring at the junction with a ferromagnet. The effect of spin-injection is to modify locally, in the ferromagnetic configuration space, the density of magnetic moments. The corresponding gradient leads to a current-dependent diffusion process of the magnetization. In order to describe this effect, the dynamics of the magnetization of a ferromagnetic single domain is reconsidered in the framework of the thermokinetic theory of mesoscopic systems. Assuming an Onsager cross-coefficient that couples the currents, it is shown that spin-dependent electric transport leads to a correction of the Landau-Lifshitz-Gilbert equation of the ferromagnetic order parameter with supplementary diffusion terms. The consequence of spin-injection in terms of activation process of the ferromagnet is deduced, and the expressions of the effective energy barrier and of the critical current are derived. Magnetic fluctuations are calculated: the correction to the fluctuations is similar to that predicted for the activation. These predictions are consistent with the measurements of spin-transfer obtained in the activation regime and for ferromagnetic resonance under spin-injection.