Magnetic anisotropy and exchange paths for octa- and tetrahedrally coordinated Mn$^{2+}$ ions in the honeycomb multiferroic Mn$_2$Mo$_3$O$_8$

TL;DR

This study explores the magnetic properties and anisotropy of Mn$^{2+}$ ions in Mn$_2$Mo$_3$O$_8$, revealing how different coordination environments influence magnetic behavior through experimental and theoretical analysis.

Contribution

It provides a detailed analysis of magnetic anisotropy and exchange interactions in Mn$_2$Mo$_3$O$_8$, combining experimental spectroscopy with ab initio calculations to assign anisotropies to specific sites.

Findings

Magnetic field dependence of spin-wave resonances explained by a two-sublattice model.

Weak easy-plane and easy-axis anisotropies identified for tetrahedral and octahedral sites.

Ab initio calculations assign anisotropies to specific Mn$^{2+}$ coordination sites.

Abstract

We investigated the static and dynamic magnetic properties of the polar ferrimagnet Mn$_2$Mo$_3$O$_8$ in three magnetically ordered phases via magnetization, magnetic torque, and THz absorption spectroscopy measurements. The observed magnetic field dependence of the spin-wave resonances, including Brillouin zone-center and zone-boundary excitations, magnetization, and torque, are well described by an extended two-sublattice antiferromagnetic classical mean-field model. In this orbitally quenched system, the competing weak easy-plane and easy-axis single-ion anisotropies of the two crystallographic sites are determined from the model and assigned to the tetra- and octahedral sites, respectively, by ab initio calculations.