Magneto-Optical Effects of Tetrahedrally Coordinated Co2+ in Ferrites II: Effects of Low Symmetry Crystal Field S4 on Faraday Rotation Spectrum.

The effect of the low-symmetry crystal field S₄ on the spectral shape of Faraday rotation in ferrites containing tetrahedral Co²⁺ ions was investigated. The calculated shape of Faraday rotation in ⁴T₁ (⁴F) becomes broad with increasing a´, a parameter proportional to the magnitude of the S4 low-symmetry field, above about a´ = 1000cm^-1 and has a shoulder or other structure when a´ ~ 2000 cm^-1. Using the value a´ = 2000 cm^-1, it is possible to explain satisfactorily the broad shape of the experimentally observed Faraday rotation at about 1.5 μm in a (Y_2.8 Gd_0.2)(Fe_4.6Co_0.2Ge_0.2)O₁₂ thin film grown by the conventional liquid phase epitaxy (LPE) method.