Instability of magnons in two-dimensional antiferromagnets at high magnetic fields

Abstract

Spin dynamics of the square lattice Heisenberg antiferromagnet, ${\text{Ba}}_{2}{\text{MnGe}}_{2}{\text{O}}_{7}$, is studied by a combination of bulk measurements, neutron diffraction, and inelastic neutron-scattering techniques. Easy plane type antiferromagnetic order is identified at $T\ensuremath{\le}4.0\text{ }\text{K}$. The exchange interactions are estimated as ${J}_{1}=27.8(3)\text{ }\ensuremath{\mu}\text{eV}$ and ${J}_{2}=1.0(1)\text{ }\ensuremath{\mu}\text{eV}$, and the saturation field ${H}_{\text{C}}$ 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 $0.7{H}_{\text{C}}\ensuremath{\lesssim}H\ensuremath{\lesssim}0.85{H}_{\text{C}}$.