Current induced spin injection and surface torque in ferromagnetic metallic junctions

TL;DR

This paper theoretically investigates how current-induced spin injection and surface torque influence spin-wave stability and magnetization in ferromagnetic metallic junctions, revealing thresholds and resonance phenomena.

Contribution

It introduces a coupled equation model for spin injection and surface torque effects, deriving a dispersion relation for current-dependent spin waves and analyzing their stability.

Findings

Spin injection and torque jointly lower instability thresholds.

Current increases lead to spin-wave pinning and new resonance lines.

Spin-wave frequency softens near the instability threshold.

Abstract

Joint influence of two effects, namely, nonequilibrium spin injection by current, and current induced surface torque, on spin-valve type ferromagnetic metallic junctions is considered theoretically. The CPP configuration is assumed. The consideration is based on solving a coupled set of equations of motion for the mobile electron and lattice magnetizations. Boundary conditions are derived from the total magnetization flux continuity condition. A dispersion relation is derived for current dependent spin-wave fluctuations. The fluctuations become unstable under current density exceeding some threshold value. Joint action of the longitudinal spin injection and the torque lowers the instability threshold. The spin injection softens spin wave frequency near the threshold and can pin magnetization at the injecting contact. The pinning rises under the current increasing, so that the appearance of new spin-wave resonance lines can be observed.