Diffusive spin-transfer: a derivation of the critical current from the spin-accumulation

摘要

The goal of this paper is to demonstrate the relevance of the non-equilibrium thermodynamic approach in the context of spin-transfer mechanism. Spin-transfer is the generic name for the effect of magnetization reversal (or magnetic excitation) produced by the injection of a spin-polarized current in a ferromagnetic layer. Deterministic vs. stochastic approaches are first defined in the context of the Landau-Lifshitz Gilbert equation of the magnetization. We then presents a model based on non-equilibrium thermodynamics in which the spin-accumulation at the interface appears as diffusion terms in the Landau-Lifshitz equation. The expression of the critical current I_c is derived from this diffusive process, and compared to the experimental results. Due to the definition of the critical current in terms of activation process, the phenomenological expression of I_c is identical to that derived in the deterministic case, after introducing an "efficiency parameter". Only the specific form of this efficiency parameters allows to discriminate between the different models. The direct link to the integral of the magnetoresistance of the junction derived here allows some highly specific behaviour to be predicted.