Magnetooptical Kerr Spectra in Sputtered Strontium Ferrite Films

Abstract
Magnetooptic (MO) polar Kerr effect spectra and MO hysteresis loops of SrFe₁₂O₁₉ hexagonal ferrite films are presented. The films were prepared by rf sputtering and subsequently annealed at 800 or 900°C in O₂/Ar. The crystallographic orientation with the c-axis perpendicular to the film plane was checked using XRD. The films display perpendicular magnetic anisotropy and rectangular hysteresis loops with a remanence ratio close to one. At low photon energies below the absorption edge of SrFe₁₂O₁₉ at 2.5 eV MO spectra are affected by the radiation penetration into the film and the quartz substrate. Above this energy they display the features typical for bulk SrFe₁₂O₁₉ crystals. The coercive field, structure of the MO spectra and the magnitude of the prominent peak in the spectra near 4.5 eV can be correlated with the structural quality of the films. Consequently, the magnetooptics can serve as a diagnostics tool for these films.