Magnetic Studies of Some Orthoferrites

This paper describes a method to distinguish between two mechanisms that may cause weak ferromagnetism in the orthoferrites, i.e., antisymmetric exchange and single-ion magnetocrystalline anisotropy. The free energy of a magnetic crystal is expressed as a series in the applied field. The condition of invariance of the energy with respect to the magnetic point group of the crystal, determines the coefficients of the energy series that are needed to describe the magnetic properties of the crystal. Magnetization and static torque measurements make possible the evaluation of these coefficients, including those of the terms cubic in the applied field. These coefficients are also calculated for the antisymmetric exchange and the single-ion magnetocrystalline anisotropy interactions. The comparison between the measured and calculated coefficients shows that in the orthoferrites the antisymmetric exchange mechanism is predominant. The method described is quite general and should be applicable to a variety of other materials.