Unidirectional spin waves measured using propagating spin wave spectroscopy

TL;DR

This paper introduces a method to analyze unidirectional spin waves using propagating spin wave spectroscopy, revealing unique phase behaviors and addressing challenges in identifying wavevectors in such systems.

Contribution

The authors develop a novel analysis technique for unidirectional spin waves, enabling accurate dispersion measurements despite spectral identification difficulties.

Findings

Unidirectional spin waves confirmed in a synthetic antiferromagnet

Phase accumulation depends on antenna width and decay length

Method improves accuracy of dispersion relation measurements

Abstract

The dispersion relation of spin waves can vary monotonically about the center of the Brillouin zone, allowing zero-momentum wavepackets to flow unidirectionally, which is of interest for applications. Techniques such as propagating spin wave spectroscopy are inoperative in such cases because of the difficulty to identify the spin wave wavevector at a particular frequency within a spectrum. Here we present a method to analyse this case and apply it to acoustic spin waves in a synthetic antiferromagnet in the scissors state, in which we confirm that propagation parallel to the applied fields is unidirectional. Interestingly, we find that in this unidirectional situation, the phase accumulated by the spin waves propagating between two antenna is not proportional to the antenna spacing. It is also a function of the two other lengths of the problem: the antenna width and the spin wave decay length. Accounting for them is required to avoid wavevector errors in the dispersion relations.