Magnon gap excitations in van der Waals antiferromagnet MnPSe$_3$

TL;DR

This study uses magneto-spectroscopy to reveal gapped magnon excitations in MnPSe$_3$, demonstrating its biaxial antiferromagnetic nature with specific anisotropy characteristics.

Contribution

It provides the first detailed characterization of magnon gaps and anisotropy in MnPSe$_3$ using magneto-spectroscopy, highlighting its biaxial antiferromagnetic properties.

Findings

Two low-energy magnon gaps at 14 and 0.7 cm$^{-1}$.

MnPSe$_3$ is identified as a biaxial antiferromagnet.

Strong out-of-plane anisotropy with weaker in-plane anisotropy.

Abstract

Magneto-spectroscopy methods have been employed to study the zero-wavevector magnon excitations in MnPSe$_3$. Experiments carried out as a function of temperature and the applied magnetic field show that two low-energy magnon branches of MnPSe$_3$ in its antiferromagnetic phase are gapped. The observation of two low-energy magnon gaps (at 14 and 0.7 cm$^{-1}$) implies that MnPSe$_3$ is a biaxial antiferromagnet. A relatively strong out-of-plane anisotropy imposes the spin alignment to be in-plane whereas the spin directionality within the plane is governed by a factor of 2.5 $\times$ 10$^{-3}$ weaker in-plane anisotropy.