Theory of Magnetodynamics Induced by Spin Torque in Perpendicularly Magnetized Thin Films

TL;DR

This paper develops a nonlinear theoretical model for spin wave excitation in thin ferromagnetic films, predicting high-frequency dynamics and nonlinear effects relevant to recent spin-torque experiments.

Contribution

It introduces a cubic complex Ginzburg-Landau type equation to describe magnetodynamics induced by spin torque, providing new insights into high-frequency excitations and nonlinear frequency shifts.

Findings

Predicts excitation frequencies over 0.2 THz for small contact diameters

Shows saturation and red shift of frequency at high currents

Modeled nonlinear frequency shifts with perturbation techniques

Abstract

A nonlinear model of spin wave excitation using a point contact in a thin ferromagnetic film is introduced. Large-amplitude magnetic solitary waves are computed, which help explain recent spin-torque experiments. Numerical simulations of the fully nonlinear model predict excitation frequencies in excess of 0.2 THz for contact diameters smaller than 6 nm. Simulations also predict a saturation and red shift of the frequency at currents large enough to invert the magnetization under the point contact. The theory is approximated by a cubic complex Ginzburg-Landau type equation. The mode's nonlinear frequency shift is found by use of perturbation techniques, whose results agree with those of direct numerical simulations.