Current-induced spin injection and surface torque in ferromagnetic metallic junctions

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Abstract
The joint influence of two current-induced effects, namely, longitudinal nonequilibrium spin injection and surface torque, on spin-valve-type ferromagnetic metallic junctions is considered theoretically. The current flows normally to layer boundaries. The analysis is based on solving a system of coupled equations of motion for mobile electron and lattice magnetizations. The boundary conditions for the equations of motion are derived from the continuity condition for the total magnetization flux in these subsystems. A dispersion relation is derived for spin wave fluctuations depending on the current through the junction. The fluctuations become unstable at currents exceeding some threshold value (usually, 106−3 × 107 A/cm2). The joint action of longitudinal spin injection and torque lowers the instability threshold. Current-induced spin injection decreases spin wave frequencies near the threshold and can strengthen magnetization pinning at the injecting contact.