# Indirect observation of phase conjugate magnons from non-degenerate four-wave mixing

## TL;DR

This paper demonstrates the first experimental realization of a phase conjugate mirror using four-wave mixing in a magnetic system, supported by simulations and theory, with potential applications in magnonic devices.

## Contribution

It introduces the first experimental demonstration of phase conjugation of magnons via four-wave mixing in a magnetic system, combining experimental data with simulations and theoretical analysis.

## Key findings

- Observation of a signal at frequency 2f1 - fp indicating phase conjugation
- Signal amplitude depends on magnetic field and mode structures
- Experimental results align with theoretical predictions of phase conjugate magnons

## Abstract

A phase conjugate mirror utilising four-wave mixing in a magnetic system is experimentally realised for the first time. Indirect evidence of continuous-wave phase conjugation has been observed experimentally and is supported by simulations. The experiment utilizes a pump-probe method to excite a four-wave mixing process. Two antennae are used to pump a region of a thin-film yttrium iron garnet waveguide with magnons of frequency $f_{1}$ to create a spatio-temporally periodic potential. As the probe magnons of $f_{\mathrm{p}}$ impinge on the pumped region, a signal with frequency $f_{\mathrm{c}} = 2f_{1}-f_{\mathrm{p}}$ is observed. The amplitude of the nonlinear signal was highly dependent on the applied magnetic field $H$. Width modes of the probe magnons and standing wave modes of the pump magnons were shown to affect the amplitude of the signal at $f_{\mathrm{c}}$. Experimental data is compared with simulations and theory to suggest that $f_{\mathrm{c}}$ is a phase conjugate of $f_{\mathrm{p}}$.