Spontaneous decays of magneto-elastic excitations in noncollinear antiferromagnet (Y,Lu)MnO3

TL;DR

This study investigates the spontaneous decay of magnetoelastic excitations in noncollinear antiferromagnets, revealing strong magnon-phonon coupling effects and anharmonicity through experimental measurements and theoretical calculations in (Y,Lu)MnO3.

Contribution

It provides the first detailed experimental and theoretical analysis of magnetoelastic excitations and their decay in noncollinear antiferromagnets, highlighting the role of magnon-phonon coupling.

Findings

Identification of a hybrid magnetoelastic mode in (Y,Lu)MnO3

Quantification of decay rates and exchange-striction coupling

Demonstration of enhanced anharmonicity due to strong magnon-phonon coupling

Abstract

When magnons and phonons, the fundamental quasiparticles of the solid, are coupled to one another, they form a new hybrid quasi-particle, leading to novel phenomena and interesting applications. Despite its wide-ranging importance, however, detailed experimental studies on the underlying Hamiltonian is rare for actual materials. Moreover, the anharmonicity of such magnetoelastic excitations remains largely unexplored although it is essential for a proper understanding of their diverse thermodynamic behaviour as well as intrinsic zero-temperature decay. Here we show that in noncollinear antiferromagnets, a strong magnon-phonon coupling can significantly enhance the anharmonicity, resulting in the creation of magnetoelastic excitations and their spontaneous decay. By measuring the spin waves over the full Brillouin zone and carrying out anharmonic spin wave calculations using a Hamiltonian with an explicit magnon-phonon coupling, we have identified a hybrid magnetoelastic mode in (Y,Lu)MnO3 and quantified its decay rate and the exchange-striction coupling term required to produce it. Our work has wide implications for understanding of the spin-phonon coupling and the resulting excitations of the broad classes of noncollinear magnets.