Spin-transfer-torque resonant switching and injection locking in presence of a weak external microwave field for spin valves with perpendicular materials

TL;DR

This study uses micromagnetic simulations to explore how weak microwave fields influence spin-transfer-torque driven magnetization dynamics in perpendicular spin valves, revealing resonant switching and injection locking phenomena.

Contribution

It provides a systematic analysis of microwave-induced effects on magnetization dynamics, combining numerical simulations with analytical theory for the first time in this context.

Findings

Resonant switching occurs near the main pre-switching mode frequency.

Injection locking bandwidth depends linearly on the locking force.

Good agreement between simulations and analytical models in certain regimes.

Abstract

The effects of a weak microwave field in the magnetization dynamics driven by spin-transfer-torque in spin-valves with perpendicular materials have been systematically studied by means of full micromagnetic simulations. In the system we studied, depending on the working point (bias field and current) in the dynamical stability diagram, we observe either resonant switching and injection locking. The resonant switching, observed in the switching region, occurs when the field frequency is approaching the frequency of the main pre-switching mode giving rise to an asymmetric power distribution of that mode in the sectional area of the free layer. At the resonant frequency, the switching time is weakly dependent on the relative phase between the instant when the current pulse is applied and the microwave field. The injection locking, observed in the dynamical region, is characterized by the following properties: (i) a locking bandwidth which is linearly dependent on the force locking, and (ii) a locking for integer harmonics of the self-oscillation frequency. We compare our numerical results with analytical theory for non-autonomous non-linear system obtaining a good agreement in the current region where the oscillation frequency and output power are characterized from a linear relationship.