Magnetic spectrum of the two-dimensional antiferromagnet La2CoO4 studied by inelastic neutron scattering

TL;DR

This study investigates the magnetic excitation spectrum of La2CoO4 using inelastic neutron scattering, revealing spin-wave modes, a high-energy peak, and the influence of orbital degrees of freedom within a Heisenberg model.

Contribution

The paper provides a detailed experimental characterization of La2CoO4's magnetic spectrum and demonstrates its description through a comprehensive Heisenberg model including orbital effects.

Findings

Spin-wave modes with strong in-plane dispersion up to 60 meV

Nearly dispersionless peak at 190 meV

Magnetic spectrum explained by a Heisenberg model with orbital degrees of freedom

Abstract

We report measurements of the magnetic excitation spectrum of the layered antiferromagnet La2CoO4 by time-of-flight neutron inelastic scattering. In the energy range probed in our experiments (0-250 meV) the magnetic spectrum consists of spin-wave modes with strong in-plane dispersion extending up to 60 meV, and a nearly dispersionless peak at 190 meV. The spin-wave modes exhibit a small (~1 meV) dispersion along the magnetic zone boundary. We show that the magnetic spectrum can be described very well by a model of a Heisenberg antiferromagnet that includes the full spin and orbital degrees of freedom of Co2+ in an axially-distorted crystal field. The collective magnetic dynamics are found to be controlled by dominant nearest-neighbour exchange interactions, strong XY-like single-ion anisotropy and a substantial unquenched orbital angular momentum.