Spin Order and Excitations in Triangular Antiferromagnet La2Ca2MnO7

TL;DR

This study investigates the magnetic order and excitations in La2Ca2MnO7, revealing a two-dimensional three-sublattice order and magnon breakdown, challenging existing theoretical models of triangular antiferromagnets.

Contribution

It provides experimental evidence of spin order and excitation spectra in a triangular antiferromagnet, highlighting deviations from linear spin-wave theory and indicating magnon breakdown.

Findings

Three-sublattice order develops below 2.80 K

Spin excitations deviate from linear spin-wave theory

Magnon breakdown occurs in the material

Abstract

We report a spin S = 3/2 triangular antiferromagnet with nearest-neighbor coupling J = 0.29 meV in La2Ca2MnO7. A genuinely two-dimensional, three-sublattice order develops below 2.80 K << the Weiss constant (25 K). The spin excitations deviate substantially from linear spin-wave theory, suggesting that magnon breakdown occurs in the material. Such a breakdown has been anticipated in recent theoretical studies, although the excitation spectrum remains to be accounted for.