Magnetic properties of ErIG and approximation of isotropic exchange

A one-ion model calculation which considers the Er³⁺ ion subject to the crystal field, the isotropic exchange field and the applied magnetic field is compared with the following experimental data: the easy axis direction, the transition temperature, the temperature and field dependence of the magnetization, the compensation temperature, the magnetocrystalline anisotropy and the umbrella structure of Er³⁺ magnetic moments in ErIG. The crystal field parameters in Y(Er)GG and ErGG are discussed and determined first. The same parameters are used for ErIG, only those of second order are allowed to vary. In spite of the isotropic exchange approximation, the experiments (except the controversial umbrella structure and anisotropy data) are well reproduced within the framework of this model. Further improvements are expected by inclusion of the anisotropy of the exchange interaction.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.