Elastic and inelastic neutron-scattering studies reveal details of the antiferromagnetic transition and intriguing spin dynamics in the magnetoelectric effect single crystal ${\text{LiMnPO}}_4$. The elastic-scattering studies confirm that the system is antiferromagnetic below $T_N=33.75\text{K}$ with local magnetic moments (${\text{Mn}}^{2+}$; $S=5/2$) that are aligned along the crystallographic $a$ axis. The spin-wave dispersion curves propagating along the three principal axes, determined by inelastic scattering, are adequately modeled in the linear spin-wave framework assuming a spin Hamiltonian that is parametrized by inter- and in-plane nearest- and next-nearest-neighbor interactions and by easy-plane anisotropy. The temperature dependence of the spin dynamics makes this an excellent model many-body spin system to address the question of the relationship between spin-wave excitations and the order parameter.

• Received 6 November 2008

DOI:https://doi.org/10.1103/PhysRevB.79.144410