Depth-dependent lattice parameter variation and stress-induced magnetic anisotropy of ultrathin Dy2BiFe4GaO12 garnet films deposited on the glass substrate by pyrolysis

Abstract

Lattice parameter variation as a function of depth from the free surface of ultrathin Dy2BiFe4GaO12 garnet films for magneto-optic application has been investigated. These thin films were synthesized by pyrolysis on the glass substrate and annealed at 660 °C in the glass transition range. The lattice parameters were determined by grazing incidence x-ray in asymmetric Bragg diffraction. X-ray diffraction results show that film stress is compressively greater near the glass/film interface and becomes smaller in magnitude toward the free-film surface. This observation has been interpreted as a result of softening of the glass substrate during annealing in the glass transition range and the subsequent larger shrinkage of the glass substrate with respect to the deposited crystalline film upon cooling. The thermal expansion difference between the substrate and the deposited film can in turn cause the stress-induced magnetic anisotropy. The induced magnetic anisotropy factor Ku has the maximum value above a threshold film thickness, about 600 Å. Down to this limit, Ku increases with the decreasing film thickness.