Annealing effects and charge compensation mechanism in calcium-doped Y3Fe5O12 films

A large series of calcium-doped Y3Fe5O12 (YIG) films were investigated to determine their behaviour upon annealing in air at temperatures between 100 and 700 °C, and upon treatment with reducing and oxidizing solutions at 100 °C. On the basis of the observed changes in the mismatch, and of the optical and electrical properties of the films, it was concluded that for the as-grown Ca, YIG films in which the calcium content is smaller than the sum of the platinum and lead content the charge compensation is accomplished by the self-compensating ability of the lead ions. For the samples in which the calcium content is larger than the sum of the platinum and lead content the charge compensation is performed by electron holes on the oxygen ions rather than by the introduction of Fe4+ ions. Treatment of the samples with a FeCl2 solution or annealing at 250 °C results in a reduction of the Pb4+ ions and as a consequence in the creation of oxygen vacancies. Reoxidation of the reduced samples can be accomplished by treating the samples in a KMnO4 solution or by annealing at 600 °C. Magnetic measurements showed that the saturation magnetization is not affected by annealing or treatment with oxidizing or reducing solutions. The small changes observed in the uniaxial anisotropy on reduction of the samples could well be explained by the changes in the lattice constant resulting in changes in the stress-induced anisotropy. The reaction rate of the reduction of Ca,YIG films is determined by the relative reaction rates of the surface process and the oxygen diffusion process of the film. In the case where the surface process is much faster than the oxygen diffusion, a diffusion rate of 7.4 μm/h at 100 °C was observed.