Influence of ionic migration induced by heat treatment on the Faraday rotation of PrxY3-xGayFe5-yO12garnets

The Faraday rotation of a Pr1.08Y1.92Ga1.11Fe3.89O12single crystal has been measured at 1.15 μm wavelength for 77< T <300 K and magnetic field applied along the [111] direction after different heat treatments. These heat treatments consisted of annealing under oxygene atmosphere at 1073, 1123, 1300 and 1473 K during a time long enough to allow the migration of gallium between the "a" and "d" ferric sites followed by quenching in air. The spontaneous rotation of this garnet which is negative (with respect to the positive Faraday rotation of YIG) increases in absolute value when the annealing temperature is increased. The Pr³⁺rotation ΔΘF, is extracted from the data assuming that the Fe³⁺ions behaviour is similar in PrxGay:YIG and Gay:YIG. Using the Van Erk thermodynamic model with the same gallium stabilization energies in "a" and "d" sites as in Gay:YIG, we observe a linear relationship between ΔΘFand the Ga³⁺content in tetrahedral sites.