Decoherence and mode-hopping in a magnetic tunnel junction-based spin-torque oscillator

TL;DR

This paper investigates the coherence of magnetic oscillations in a spin-torque oscillator, revealing mode-hopping phenomena influenced by external field angles and couplings, which affect oscillator stability.

Contribution

It provides a detailed analysis of mode-hopping mechanisms in magnetic tunnel junction oscillators and identifies conditions minimizing this effect.

Findings

Mode-hopping occurs between distinct oscillator modes.

Mode-hopping is minimized near the antiparallel current threshold.

Away from the threshold, mode-hopping reduces oscillator coherence.

Abstract

We discuss the coherence of magnetic oscillations in a magnetic tunnel junction-based spin-torque oscillator as a function of external field angle. Time-frequency analysis shows mode-hopping between distinct oscillator modes, which arises from linear and nonlinear couplings in the Landau-Lifshitz-Gilbert equation, analogous to mode-hopping observed in semiconductor ring lasers. These couplings and therefore mode-hopping are minimized near the current threshold for antiparallel (AP) alignment of free layer with reference layer magnetization. Away from the AP alignment, mode-hopping limits oscillator coherence.