Magnetic-field-induced magnon portfolio in a van der Waals magnet

TL;DR

This study explores how magnetic fields influence magnon excitations in the van der Waals antiferromagnet CrOCl, revealing complex phase transitions and coexistence of magnetic states through broad-range absorption experiments.

Contribution

It provides the first detailed analysis of magnetic-field-induced magnon spectra and phase transitions in CrOCl, highlighting the role of competing interactions and anisotropies.

Findings

Magnon spectra exhibit strong bi-axial anisotropy at low fields.

Canted phases show unique magnon features influenced by in-plane anisotropies.

Hysteretic magnon spectra indicate coexistence of magnetic phases.

Abstract

Magnonic excitations are investigated in chromium oxychloride (CrOCl), a van der Waal (vdW) antiferromagnet prone to a multitude of magnetic phase transitions, with absorption experiments in a broad continuous energy range. At low magnetic fields, the magnon spectra show a strong bi-axial anisotropy and inform on the relative weights of the effective exchange coupling and the system anisotropies. As the magnetic field increases, magnons characteristic of a canted phase are first observed, with peculiarities attributed to in-plane anisotropies and magnon-magnon coupling. Subsequently, a hysteretic magnon spectrum appears as the system transitions to a ferrimagnetic state, with two new magnon branches partly coexisting with the lower energy canted phase branch, indicating the formation of spatially separated magnetic phases. Further changes in the magnon spectrum in higher magnetic fields accompany transitions to the different canted magnetic phases previously reported. Our experiments show that competing exchange interactions and ground states broaden the options to generate different kinds of magnonic excitations in the same vdW material upon the variation of external parameters.