Anisotropy of Fe3+ Ions in Yttrium Iron Garnet

Using the single-ion theory of anisotropy, it is possible to derive the anisotropy constants at 0°K for yttrium iron garnet in which the iron ions on tetrahedral and octahedral sites are replaced by nonmagnetic ions of gallium, indium, or scandium, respectively. The theoretical variation of K1 has been compared with experimental values derived from torque measurements on single crystals of Y3GaxFe5−xO12 (x=1.15), Y3InxFe3−xO12 (x=0.12, 0.20, 0.49), Y3ScxFe5−xO12 (x=0.87) between 1.5° and 300°K. Although the results of the tetrahedral substitution fit the sample theory, the results for octahedral substitution give values of K1 much lower than predicted. These values can be explained by assuming that the octahedral substitutions modify the crystal-field parameters of the unsubstituted Fe3+ ions and thus alter their contribution to the over-all magnetocrystalline anisotropy.