Low and very high magnetic field dependence of the magnetization and the Faraday rotation induced by the magnetic dipole transitions in YIG

From Faraday rotation experiment performed at 1.15 and 0.6328 μm wavelength under low and very high magnetic fields up to 4 MOe, the magnetic field dependences are analyzed of the magnetization and the Faraday rotation induced by the magnetic dipole transitions in both the octa‐ and tetrahedral sites of YIG. The best agreement between the magneto‐optical data under intense fields and a molecular field model iniplies a choice of the exchange parameters where the intra‐sublattice interactions must be neglected. The magnetic field dependence of the sublattices magnetization, calculated from this molecular field model follows a paramagnetic behaviour up to a spin‐flop critical field as observed in our experiment near 1.7 MOe. It is shown that the Faraday rotation induced by the magnetic dipole transitions is described from two terms having a magnetic field increase of opposite sign. The first term is the usual “magnetic” Faraday rotation proportional to the total magnetization and the second one, having a dispersive character, has a quadratic dependence on the effective field defined by the applied and exchange fields.