Magnetic Excitations in LiCoPO$_{4}$

LiCoPO$_{4}$ continues to attract much attention due to its exceptionally large magnetoelectric (ME) effect coefficient and the observed weak ferromagnetism and ME ``butterfly loop'' anomaly. To gain insight into the microscopic magnetic interactions in LiCoPO$_{4}$, inelastic neutron scattering experiments were performed in the antiferromagnetic phase at T = 8 K (T$_{N} \approx $ 21.8 K). Weak dispersion was detected in the magnetic excitation spectra along the three crystallographic axes measured around the (0 1 0) magnetic reflection. A gap of $\sim$ 4.7 meV was observed below T$_{N}$ that vanished above T$_{N}$. We analyze the data within a linear spin-wave approximation by explicitly including single-ion anisotropy terms in the Heisenberg spin Hamiltonian. The magnitude of the single-ion anisotropy is found to be comparable to the strongest nearest-neighbor magnetic interaction suggesting that the Co$^{2+}$ single ion anisotropy plays an important role in the spin dynamics of LiCoPO$_{4}$.