Infrared Faraday Rotation in Ferrites

Abstract

The absorption and Faraday rotation of crystals of the spinel ferrites Li_0.5Fe_2.5O₄, NiFe₂O₄, and MgFe₂O₄ and of the hexagonal ferrites BaFe₁₂O₁₉ and Ba₂Zn₂Fe₁₂O₂₂ have been measured at 300°K between 1 and 8 μ. The rotation consists of a nearly wavelength‐independent term θ_M arising from the magnetic resonance and of a strongly dispersive term θ_d originating mainly from electronic transitions of Fe³⁺. As in YIG, the Fe³⁺ ions in tetrahedral and octahedral coordination contribute differently to θ_d. The experimental curves of the Faraday rotation of YIG, Li_0.5Fe_2.5O₄ and MgFe₂O₄ can be described rather accurately with the same constants for the rotary powers of Fe³⁺ in tetrahedra and of Fe³⁺ in octahedra. Also the contribution of Ni²⁺ to θ_d in NiFe₂O₄ at 80°, 300°, and 373°K has been determined.