Electron Paramagnetic Resonance of Trivalent Gadolinium in the Yttrium Gallium and Yttrium Aluminum Garnets

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Abstract
The spin Hamiltonian parameters for Gd+++ when substituted for Y+++ in two diamagnetic garnets, YAlG and YaG, have been determined by electron paramagnetic resonance techniques. From these results the contribution of the independent Gd+++ ions to the anisotropy of gadolinium iron garnets may be estimated. The fourth‐order constants in the spin Hamiltonian are very similar in YAlG and YGaG and their contribution to the anisotropy constant in GdIG shows good agreement with the experimental data. The contribution of the second‐order constants falls short of the values needed to fit experimental data by an order of magnitude. These constants, however, differ markedly in the two garnets and thus their use to predict anisotropy in GdIG is not justified. The present results, therefore, are not in disagreement with a model that ascribes the origin of the crystalline anisotropy in magnetic garnets to the anisotropy energy of the individual ions in the presence of the crystalline electrostatic field.