MICROSTRUCTURAL ORIGIN OF THE PERPENDICULAR ANISOTROPY IN M-TYPE BARIUM HEXAFERRITE THIN-FILMS DEPOSITED BY RF MAGNETRON SPUTTERING

Barium hexaferrite thin films deposited by rf magnetron sputtering have been made which exhibit saturation magnetization 90% of that of bulk single crystals, whereas the perpendicular uniaxial anisotropy is only 60% of that of the bulk. X-ray diffraction spectra suggest good c-axis orientation perpendicular to the film plane. However, M-H hysteresis loops show a fairly large in-plane hysteresis. Scanning electron microscopy and transmission electron microscopy show that the films are made of a mixture of platelet-shaped grains and acicular grains. Microdiffraction studies in a transmission electron microscope indicate that the platelets have their c-axis oriented perpendicular to the plane and that the acicular grains have c-axis orientation in the plane. Preferential grain growth in the basal plane of the crystal is believed to be responsible for these grain geometries. Because the platelets occupy a much larger volume of the film than the acicular particles, there is a preferential c-axis orientation perpendicular to the film plane.