This paI:er will review recent anisotropy data, deduced from static and resonance measurements, on the r:u-e-earth lron ga:nets of formula 5Fe2C?a 3M20 3, where M i~ Y, Gd, Vb, Er, Sm, Tb, Dy, and Ho, respectively. Both the hIgh temperature behavlOr (up to 300 0 K) whIch can be expressed in terms of the anisotropy const~nts KI a.r:d K2 and the ~nomalous ~nisotropy properties which occur at liquid helium temperatures are dl.scussed. 'Ihe results are mterpreted III terms of the single ion model which considers the anisotropy resu!tIn,g from the effe.ct .of the combined crystal and exchange fields of the garnet on the energy levels of ~he IlldlVldual.magnet~c IOns, and the extent to which this model can describe the anisotropy of rare-earth Iron garnets wIll be brIefly discussed.

Measurements of the Faraday rotation in YIG and TbIG have been made as a function of temperature in the range 100°–450°K at the helium-neon laser wavelength of 1.15 μ. This wavelength lies on the edge of the YIG window at the short-wavelength absorption limit. Measurements were made on single-crystal blocks of YIG and TbIG up to 7 mm thick in applied fields of up to 10 kOe. In YIG the major contribution to the Faraday rotation at this wavelength is the dispersive part associated with absorption bands in the visible and near ir. This contribution reaches a maximum of 188°/cm at 280°K and can be fitted to the sublattice magnetization data of Anderson. For TbIG we find αF = 448°/cm at 300°K and a very strong temperature dependence. In addition we observe a field-dependent Faraday rotation of −3.8°/cm/kOe at 300°K. Extrapolation of the observed rotations to zero internal field removes he discontinuity in | αF | which otherwise appears at the compensation temperature (245°K). The zero-field Faraday rotation may be analyzed in terms of three contributions: a nondispersive part arising from the exchange resonance, a dispersive part arising from the Fe3+ sublattices, and a dispersive contribution from the Tb3+ sublattice. Additional information on the Tb3+ contribution was obtained from Verdet constant measurements on TbGaG and TbAlG.

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Torque measurements have been made at 4.2°K on crystals of silicon-doped yttrium iron garnet which were irradiated with infrared light. The radiation caused large photomagnetic anneal effects which were found to depend on the plane of polarization of the light.

Using the single-ion theory of anisotropy, it is possible to derive the anisotropy constants at OaK 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 KI has been compared with experimental values derived from torque measurements on single crystals of Y.Ga.Fe6-Z012 (x = 1.15), Y.ln.Fe.-z012 (x=0.12, 0.20, 0.49), Y.Sc.Fe6_z012 (x=0.87) between 1.5° and 300 0 K. Although the results of the tetrahedral substitution fit the sample theory, the results for octahedral substitution give values of KI much lower than predicted. These values can be explained by assuming that the octahedral substitutions modify the crystal-field parameters of the unsubstituted Fe H ions and thus alter their contribution to the over-all magnetocrystalline anisotropy.