A theoretical study of the magnetic and magneto-optical properties of Nd-substituted yttrium iron garnets

The neodymium substitution in yttrium iron garnet induces a large enhancement of the Faraday rotation although the magnetic moment of the Nd 3+ ion in yttrium iron garnet is very small. A detailed theoretical analysis of both magnetic and magneto-optical (MO) properties in Nd x Y 3- x Fe 5 O 12 using the quantum theory is developed. The intra-ionic electric dipole transitions between the 4f 3 and 4f 2 5d configuration split states are studied taking into account the spin-orbit, crystal field and super-exchange interaction perturbations. For the excited configuration, the coupling scheme of Yanase is extended to the Nd 3+ ion. A good agreement between experimental and calculated values is obtained for the temperature dependence of both the magnetic moment and Faraday rotation, and the MO resonance frequencies. Attention is paid to the mixing of the ground state multiplets. It is concluded that the Faraday rotation is well described by the intra-ionic electric dipole transition model and is unambiguously of the paramagnetic type.