Multiple types of Fe4+ centers in Ca-doped YIG films

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Abstract
The effect of annealing in reducing atmosphere on Ca‐doped YIG films are studied by means of magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) in the near infrared. The LPE films had ‖110‖ and [100] orientation and the Ca content was about 0.1 atoms/formula unit. The MDC spectra are found to change shape dramatically after the first milder reducing treatments, then a definite and constant shape is acquired, the corresponding amplitude scaling down linearly with absorption until attainment of full infrared transparency. Such a behavior suggests the presence in the films of more than one type of Fe4+ centers which are reduced at different rates during the initial treatments, until a single type eventually prevails. Furthermore, an AVIA experiment indicates that the Fe4+ centers being reduced at a faster rate have markedly different orientational properties than the later ones, with in‐plane MLD about 20 times smaller. The results are explained in terms of different acceptor centers being involved in the earlier and later stages of the reducing treatments and are assumed responsible for the recently reported nonlinear behavior and for increasing oxygen‐vacancies concentration of the uniaxial anisotropy constant of YIG:Ca films.