Nonreciprocal Spin Waves Driven by Left-Hand Microwaves

TL;DR

This paper demonstrates that left-hand microwaves can excite nonreciprocal spin waves in ferromagnets under certain conditions, revealing a new mechanism for controlling magnonic signals and enabling diode-like functionalities.

Contribution

It reveals how ellipticity mismatch enables left-hand microwaves to excite nonreciprocal spin waves, challenging conventional wisdom and introducing a tunable mechanism for magnonic control.

Findings

Identification of a critical frequency where left-hand microwaves cannot excite spin waves.

Demonstration of switchable nonreciprocal spin wave propagation by tuning microwave frequency.

Proposal of a mode-dependent mutual demagnetizing factor to explain the phenomena.

Abstract

It is a conventional wisdom that a left-hand microwave cannot efficiently excite the spin wave (SW) in ferromagnets, due to the constraint of angular momentum conservation. In this work, we show that the left-hand microwave can drive nonreciprocal SWs in the presence of a strong ellipticity-mismatch between the microwave and precessing magnetization. A critical frequency is predicted, at which the left-hand microwave cannot excite SWs. Away from it the SW amplitude sensitively depends on the ellipticity of left-hand microwaves, in sharp contrast to the case driven by right-hand ones. By tuning the microwave frequency, we observe a switchable SW non-reciprocity in a ferromagnetic single layer. A mode-dependent mutual demagnetizing factor is proposed to explain this finding. Our work advances the understanding of the photon-magnon conversion, and paves the way to designing diode-like functionalities in nano-scaled magnonics.