Spin excitations in the magnetically ordered phases of MnSc$_2$S$_4$

TL;DR

This study investigates spin excitations in MnSc$_2$S$_4$ using THz spectroscopy, revealing a single magnetic resonance and insights into weak anisotropies and low-frequency modes related to its frustrated magnetic phases.

Contribution

The paper provides the first detailed THz spectroscopic analysis of MnSc$_2$S$_4$, identifying a single magnetic resonance and characterizing its magnetic excitations in the context of frustrated magnetism.

Findings

Single magnetic resonance with linearly increasing frequency in magnetic field

g-factor of Mn$^{2+}$ ions determined as 1.96

Presence of low-frequency modes below 100 GHz

Abstract

Recent neutron scattering experiments suggested that frustrated magnetic interactions give rise to antiferromagnetic spiral and fractional skyrmion lattice phases in MnSc$_2$S$_4$. Here, to trace the signatures of these modulated phases, we studied the spin excitations of MnSc$_2$S$_4$ by THz spectroscopy at 300 mK up to 12 T. We found a single magnetic resonance with linearly increasing frequency in field. The corresponding $g$-factor of Mn$^{2+}$ ions $g$ = 1.96, and the absence of other resonances imply very weak anisotropies and negligible contribution of higher harmonics to the spiral state. The significant difference between the dc magnetic susceptibility and the lowest-frequency ac susceptibility in our experiment implies the existence of mode(s) below 100 GHz.