Dynamics of two coupled vortices in a spin valve nanopillar excited by spin transfer torque

TL;DR

This paper explores the behavior of two coupled magnetic vortices in a spin valve nanopillar under spin transfer torque, demonstrating controllable dynamics and high coherence in microwave signals, relevant for spintronic applications.

Contribution

It introduces a method to independently control and detect coupled vortex states, revealing high-coherence microwave emissions influenced by vortex polarities.

Findings

Coherent microwave signals with linewidth down to 46 kHz observed at high current densities.

Signal coherence persists even at zero magnetic field.

Emission frequency varies linearly with perpendicular magnetic field.

Abstract

We investigate the dynamics of two coupled vortices driven by spin transfer. We are able to independently control with current and perpendicular field, and to detect, the respective chiralities and polarities of the two vortices. For current densities above $J=5.7*10^7 A/cm^2$, a highly coherent signal (linewidth down to 46 kHz) can be observed, with a strong dependence on the relative polarities of the vortices. It demonstrates the interest of using coupled dynamics in order to increase the coherence of the microwave signal. Emissions exhibit a linear frequency evolution with perpendicular field, with coherence conserved even at zero magnetic field.