Equilibrium Spin Configuration and Resonance Behavior of RbMnF3

The equilibrium orientations of the magnetic sublattices of the cubic antiferromagnet RbMn${\mathrm{F}}_3$ have been studied. By assuming spatially uniform magnetization and restricting the applied steady magnetic field to lie in a {110} plane, the problem is considerably simplified. The analysis enables the equilibrium spin configurations for the important cases of the magnetizing field applied along any of the three principal crystal axes to be predicted. Each case has more than one solution. The theory predicts that abrupt spin flopping from one equilibrium state to another should occur under certain conditions. An antiferromagnetic-resonance theory is presented which is applicable over a wide range of field and embraces the low- and high-field resonance theories previously reported as restricted examples. Observations of the resonance spectrum at $X$-band frequencies for the applied field range 0 to 12 kOe are presented. The measurements provide excellent verification of the resonance theory and confirm the validity of the equilibrium analysis. The best fit between theory and experiment was obtained by assuming values of the anisotropy field significantly different from the previously published value. Abrupt spin flopping was not observed. The resonance data indicate that the magnetization can switch between equilibrium directions gradually over a range of field and at much lower field strengths than the theoretical flopping field.