Large-amplitude coherent spin waves exited by spin-polarized current in nanoscale spin valves

TL;DR

This paper investigates large-amplitude coherent spin wave excitations driven by spin-polarized current in nanoscale spin valves, revealing mode transitions and comparing experimental results with micromagnetic simulations.

Contribution

It provides detailed spectral measurements of spin-wave excitations and evaluates the accuracy of LLGS micromagnetic simulations in describing these phenomena.

Findings

Large-amplitude coherent spin waves are excited over a wide current range.

Frequency jumps occur due to mode transitions between localized nonlinear spin waves.

LLGS simulations accurately predict mode transition behavior but not excitation amplitudes.

Abstract

We present spectral measurements of spin-wave excitations driven by direct spinpolarized current in the free layer of nanoscale Ir20Mn80/Ni80Fe20/Cu/Ni80Fe20 spin valves. The measurements reveal that large-amplitude coherent spin wave modes are excited over a wide range of bias current. The frequency of these excitations exhibits a series of jumps as a function of current due to transitions between different localized nonlinear spin wave modes of the Ni80Fe20 nanomagnet. We find that micromagnetic simulations employing the Landau-Lifshitz-Gilbert equation of motion augmented by the Slonczewski spin torque term (LLGS) accurately describe the frequency of the current-driven excitations including the mode transition behavior. However LLGS simulations give qualitatively incorrect predictions for the amplitude of excited spin waves as a function of current.