Spin dynamics and exchange interactions in CuO measured by neutron scattering

TL;DR

This study uses neutron scattering to map the spin dynamics and exchange interactions in CuO, revealing continuum features at high energies and a good fit to a spin-wave model at lower energies, with implications for multiferroicity.

Contribution

It provides a comprehensive experimental characterization of CuO's spin dynamics and determines exchange constants using neutron scattering and spin-wave modeling.

Findings

High-energy continuum features consistent with $S=1/2$ Heisenberg chain

Low-energy spectrum well-described by linear spin-wave model

Unexplained low-energy features in the high-temperature phase

Abstract

The magnetic properties of CuO encompass several contemporary themes in condensed matter physics, including quantum magnetism, magnetic frustration, magnetically-induced ferroelectricity and orbital currents. Here we report polarized and unpolarized neutron inelastic scattering measurements which provide a comprehensive map of the cooperative spin dynamics in the low temperature antiferromagnetic (AFM) phase of CuO throughout much of the Brillouin zone. At high energies ($E \gtrsim 100$\,meV) the spectrum displays continuum features consistent with the des Cloizeax--Pearson dispersion for an ideal $S=\frac{1}{2}$ Heisenberg AFM chain. At lower energies the spectrum becomes more three-dimensional, and we find that a linear spin-wave model for a Heisenberg AFM provides a very good description of the data, allowing for an accurate determination of the relevant exchange constants in an effective spin Hamiltonian for CuO. In the high temperature helicoidal phase, there are features in the measured low-energy spectrum that we could not reproduce with a spin-only model. We discuss how these might be associated with the magnetically-induced multiferroic behavior observed in this phase.