Coupled Antiferromagnetic-Nuclear-Magnetic Resonance inRbMnF3

The coupling between antiferromagnetic and ${\mathrm{Mn}}^{55}$ nuclear resonances in ${\mathrm{RbMnF}}_3$ has been studied both theoretically and experimentally. The electronic and nuclear frequencies have been derived by solving the coupled equations of motion for (a) a four-sublattice model, consisting of two electronic and two nuclear magnetic sublattices; (b) a two-sublattice model in which the electron-nuclear interaction is represented by a static anisotropy field. For the electronic modes, the differences in the frequencies obtained from the two models are negligible. However, only the four-sublattice theory predicts the NMR frequencies to good accuracy, for applied fields both greater and less than the spin-flop value. The temperature dependence of the crystal parameters has been included, and comparison is made between theory and experiment in the temperature range where the parallel susceptibility is significant.