Spin-torque driven ferromagnetic resonance in a nonlinear regime

TL;DR

This paper investigates nonlinear spin-torque driven ferromagnetic resonance in Co|Ni multilayer nanojunctions, revealing power-dependent resonance broadening, asymmetry, and a nonhysteretic step, with potential sensor applications.

Contribution

It demonstrates nonlinear effects in ST-FMR, including resonance broadening and step jumps, and compares experimental results with macrospin simulations, advancing understanding of nonlinear spin dynamics.

Findings

Resonance lines broaden and shift with power

Observation of nonhysteretic step jumps in voltage

Agreement with nonlinear oscillator models

Abstract

Spin-valve based nanojunctions incorporating Co|Ni multilayers with perpendicular anisotropy were used to study spin-torque driven ferromagnetic resonance (ST-FMR) in a nonlinear regime. Perpendicular field swept resonance lines were measured under a large amplitude microwave current excitation, which produces a large angle precession of the Co|Ni layer magnetization. With increasing rf power the resonance lines broaden and become asymmetric, with their peak shifting to lower applied field. A nonhysteretic step jump in ST-FMR voltage signal was also observed at high powers. The results are analyzed in in terms of the foldover effect of a forced nonlinear oscillator and compared to macrospin simulations. The ST-FMR nonhysteretic step response may have applications in frequency and amplitude tunable nanoscale field sensors.