Magnetism and magneto-optics of hexaferrite layers

Recent contributions to research in magnetism and magneto-optics of hexaferrite layers, resulting from the collaboration between the above-mentioned institutions, are comprehensively reviewed. The pulsed laser deposition (PLD) technique is described and its main features, relying on the plume diagnostics and correct oxygen pressure, both being important for the deposition of hexaferrites of complex stoichiometry, are highlighted. The fabricated layers were investigated structurally and it was found that they are highly textured with the c-axis perpendicular to the film plane. Their magnetization was measured over a wide temperature range, 4.2-300 K, and in fields up to 12 T. Its dependence upon the cobalt content x in BaFe12-x-yCoxTiyO19 was also determined in the interval 0 less than or equal to x less than or equal to 0.8. The results were interpreted in terms of Neel theory and this, when combined with our results of Mossbauer spectra measurements, led to the formulation of a consistent model for the cation distribution in Co-Ti-substituted barium hexaferrites. The hysteresis-loop measurements provided data for obtaining values of anisotropy, which are in agreement with those of the bulk materials. The domain structure of thin hexaferrite layers was also studied, particularly the domain period dependence upon the sample thickness and cobalt content. The domain period dependence was found to be in very good agreement with theoretical micromagnetic calculations. Ellipsometry, reflectance photometry and Kerr/Faraday polarimetry were used to determine the optical and magneto-optical properties of hexaferrite platelets and thin layers. The complex refractive index and magneto-optic parameter were determined over the spectral range 350-850 nm and the reliability of the data was tested by comparison with photometric measurements of reflectance. The Faraday rotation and absorption spectra of substituted hexaferrite thin layers were measured in the 500-2000 nm wavelength range at room temperature and 80 K. The results obtained are interpreted in terms of single-ion optical electron transitions belonging to either cobalt or iron cations occupying the tetrahedral and/or octahedral positions in the spinel block of hexagonal ferrite crystal lattice.