Superexchange field and intense magnetic field dependences of the Faraday rotation induced by the electric dipole transitions in YIG

The influence of the superexchange field on the Faraday rotation induced in YIG at 1.15 μm wavelength by electric dipole transitions is analyzed in both the octahedral and tetrahedral sites where the contributions of the strong allowed transitions and the weak “forbidden” transitions are determined. It is shown that the temperature evolution of the magneto‐optical coefficients associated with the electric dipole transitions, as deduced from experiments on YIG, is well described by an effective field model which uses the superexchange and the applied magnetic fields. From this model it is shown also that under high (≈ 10 5 Oe) and intense (> 10 6 Oe) magnetic fields, H a , the total Faraday rotation depends on H a , firstly through the direct influence of the field on the sublattice magnetization and secondly through the magnetic field dependence of the “electric” magneto‐optical coefficients in the a and d sites.