Synthesis of Z-type hexagonal ferrite films by rf magnetron sputtering techniques (abstract)

The synthesis of textured stoichiometric Z-type hexagonal ferrite films, Ba3Me2Fe24O41 (Me2-Z), where Me is a divalent ion, by sputtering techniques is reported. The compound Co2-Z shows a large planar anisotropy with a high permeability at room temperature, and thus, are promising candidates for microwave device applications. The objective here was to develop thin films of these materials for devices on integrable substrates. The films were deposited on unheated Si substrates by rf magnetron sputtering using oxide targets in a mixed argon/oxygen atmosphere. Studies on the crystal structure, composition, and magnetic properties were performed on 1.6 μm thick films. The films were characterized by x-ray diffraction and scanning electron microscopy, and the composition was analyzed by energy dispersive x-ray analysis and Auger electron spectroscopy/secondary-ion-mass-spectroscopy techniques. As-deposited films were amorphous and paramagnetic. The films were subjected, either to a rapid thermal anneal at 900 or 1000 °C for 2 min, or a conventional furnace anneal at 800 °C for 60 min. The rapid annealed films were found to contain 10%–40% of M- and Y-phases, and the saturation magnetization M was 50% smaller than the expected values. The furnace annealed films were textured with the c axis perpendicular to the film plane and showed a small amount of impurity phases. The measured M of 28.2 μB at 4.2 K is in excellent agreement with the theoretical value of 29.2 μB. Room-temperature data on the field dependence of M show a squareness ratio of 0.8 for in-plane fields and an in-plane anisotropy field on the order of 6 kOe.