Current-driven destabilization of both collinear configurations in asymmetric spin-valves

TL;DR

This paper demonstrates that in certain asymmetric spin-valves, spin current can destabilize both collinear magnetic configurations, leading to zero-field precessional modes, with phase diagrams and frequencies calculated via a macrospin model.

Contribution

It introduces the novel finding that asymmetric spin-valves can destabilize both parallel and antiparallel states, enabling zero-field precessional modes.

Findings

Both collinear configurations can be destabilized by spin current in asymmetric spin-valves.

Zero magnetic field precessional modes can occur due to this destabilization.

Phase diagrams and mode frequencies are calculated using a macrospin model.

Abstract

Spin transfer torque in spin valves usually destabilizes one of the collinear configurations (either parallel or antiparallel) and stabilizes the second one. Apart from this, balance of the spin-transfer and damping torques can lead to steady precessional modes. In this letter we show that in some asymmetric nanopillars spin current can destabilize both parallel and antiparallel configurations. As a result, stationary precessional modes can occur at zero magnetic field. The corresponding phase diagram as well as frequencies of the precessional modes have been calculated in the framework of macrospin model. The relevant spin transfer torque has been calculated in terms of the macroscopic model based on spin diffusion equations.