Dynamics and thermodynamics of the S = 5/2 almost Heisenberg triangular lattice antiferromagnet K2Mn(SeO3)2

TL;DR

This study investigates the magnetic phases and excitations of the large-S triangular lattice antiferromagnet K2Mn(SeO3)2, revealing complex spectra and the importance of magnon interactions.

Contribution

It provides detailed experimental and theoretical analysis of magnetic phases and excitations in a nearly Heisenberg S=5/2 triangular lattice antiferromagnet with weak anisotropy.

Findings

Identification of multiple magnetic phases including Y, 1/3 plateau, and V phases.

Observation of both single-magnon and high-energy continuum excitations.

Spectral features well described by non-linear spin wave theory, highlighting magnon interactions.

Abstract

We report calorimetric, magnetic, and neutron scattering studies on an S = 5/2, nearly Heisenberg triangular-lattice antiferromagnet K2Mn(SeO3)2 with weak XXZ easy-axis anisotropy. Multiple magnetic phases are identified, including a non-collinear Y phase in zero field, a field-induced collinear m = 1/3 magnetization plateau, and a high-field V phase. In the Y phase, the magnetic excitation spectrum exhibits both single-magnon excitations and an extended high-energy continuum. Both features are well described by non-linear spin wave theory. In the field-induced phases, complex effects of the spectrum renormalization even for large S = 5/2 material are clearly detectable. These results underscore the essential role of magnon-magnon interactions in the dynamics of large-S Heisenberg spin systems on a triangular lattice.