Experimental evidence of self-localized and propagating spin wave modes in obliquely magnetized current-driven nanocontacts

TL;DR

This paper presents experimental evidence of two distinct spin wave modes in nanocontact spin-torque oscillators, identifying one as a propagating wave and the other as a localized nonlinear bullet, with mode hopping caused by the Oersted field.

Contribution

It provides the first detailed experimental analysis of both self-localized and propagating spin wave modes in obliquely magnetized nanocontacts, supported by theory and simulations.

Findings

Two distinct spin wave modes with different frequencies and threshold currents

Identification of one mode as an exchange-dominated propagating wave

Observation of rapid mode hopping induced by the Oersted field

Abstract

Through detailed experimental studies of the angular dependence of spin wave excitations in nanocontact-based spin-torque oscillators, we demonstrate that two distinct spin wave modes can be excited, with different frequency, threshold currents and frequency tuneability. Using analytical theory and micromagnetic simulations we identify one mode as an exchange-dominated propagating spin wave, and the other as a self-localized nonlinear spin wave bullet. Wavelet-based analysis of the simulations indicates that the apparent simultaneous excitation of both modes results from rapid mode hopping induced by the Oersted field.