Inelastic neutron-scattering (INS) experiments were performed to investigate the spin dynamics in magnetoelectric effect ${\text{LiCoPO}}_4$ single crystals. Weak dispersion was detected in the magnetic excitation spectra along the three principal crystallographic axes measured around the (0 1 0) magnetic reflection. Analysis of the data using linear spin-wave theory indicates that single-ion anisotropy in ${\text{LiCoPO}}_4$ is as important as the strongest nearest-neighbor exchange coupling. Our results suggest that ${\text{Co}}^{2+}$ single-ion anisotropy plays an important role in the spin dynamics of ${\text{LiCoPO}}_4$ and must be taken into account in understanding its physical properties. High-resolution INS measurements reveal an anomalous low-energy excitation that we hypothesize may be related to the magnetoelectric effect of ${\text{LiCoPO}}_4$.

• Received 29 August 2008

DOI:https://doi.org/10.1103/PhysRevB.78.184429