Magnetic Anisotropy Of Antiferromagnetic Rbmnf3

RbMnF3 is known to have a very small magnetic anisotropy and to be a nearly ideal realization of a three-dimensional Heisenberg antiferromagnet. Although its critical behavior has been studied in detail, the origin of the residual magnetic anisotropy has not had sufficient attention. Here we present an experimental investigation of the temperature dependence of the anisotropy in RbMnF3 and show that it can be explained by a model for the crystal field. The experimental data are obtained with magnetization and susceptibility measurements from which we can accurately obtain the critical magnetic field for the transition from the antiferromagnetic to the spin-flop phase. The fit of the theoretical model to the data yields information on some microscopic parameters.