CHEMICAL MODIFICATION OF MAGNETOOPTIC GARNET FILM PROPERTIES

Single-crystal magneto-optic garnet films of composition (BiTm)3(FeGa)5012 have applications to spatial light modulators, optical isolators, and magnetic-field sensors. These as-grown films have a coercivity under 1 Oe and can support cm-size stable domains. It has been found that chemical treatments with oxidizing or reducing gases can reversibly modify the magnetic properties. Treatments are performed at 400-700-degrees-C for fixed times. Reducing treatments dilate the x-ray lattice constant up to 0.1%, introduce Fe2+ monitored by increased optical absorption at 1.00-1.06 pm and decrease Faraday rotation about 5% over the visible spectrum. Oxidation can partially or totally reverse these parameters. Magnetic measurements on the bulk film show that coercivity can be finely controlled, square hysteresis loops attained, and domain-wall mobility changed. At the same time the initial perpendicular anisotropy H(k) Of 8-12 kOe is decreased while the saturation magnetization (4piM(s)) of 100-150 G is affected to a minor degree. For magneto-optic imaging of defects, the resolution, contrast, and device operation are assisted favorably. Magnetic measurements are presented as a function of specific chemical treatment. The data suggest that an oxygen vacancy mechanism is operative at the film surface layers.