Instability of Magnons in Two-dimensional Antiferromagnet at High Magnetic Fields

TL;DR

This study investigates the spin dynamics of a two-dimensional square lattice antiferromagnet, revealing magnon instabilities at high magnetic fields through neutron scattering and bulk measurements.

Contribution

It provides new experimental evidence of magnon instability in a 2D antiferromagnet at high magnetic fields, combining multiple measurement techniques.

Findings

Identification of easy plane antiferromagnetic order below 4 K

Estimation of exchange interactions J1 and J2

Observation of magnon instability near 0.7 to 0.85 of the saturation field

Abstract

Spin dynamics of the square lattice Heisenberg antiferromagnet, \BaMnGeO, is studied by a combination of bulk measurements, neutron diffraction, and inelastic neutron scattering techniques. Easy plane type antiferromagnetic order is identified at $T \le 4.0$ K. The exchange interactions are estimated as $J_1$ = 27.8(3)${\mu}$eV and $J_2$ = 1.0(1) ${\mu}$eV, and the saturation field $H_{\rm C}$ is 9.75 T. Magnetic excitation measurements with high experimental resolution setup by triple axis neutron spectrometer reveals the instability of one magnon excitation in the field range of $0.7H_{\rm C} \lesssim H \lesssim 0.85H_{\rm C}$.