Magnetic properties of sputtered Fe thin films: Processing and thickness dependence

The microstructure and magnetic properties of polycrystalline Fe films with thicknesses of 200-1000 Å have been investigated. The films were prepared by rf sputtering onto SiO₂ substrates. The investigation was prompted by the lack of data on sputtered Fe films in this thickness regime as well as disagreement in the data for evaporated films. In addition to thickness, substrate temperature and deposition pressure were varied to examine their effect on the microstructure. The film microstructure was characterized by x-ray diffraction, transmission electron microscopy, and Auger spectroscopy. The polycrystalline films did not display a strong preferred orientation and had average grain sizes of 60-85 Å. Surface oxide layers formed upon exposure to air ranged from 10 to 80 Å, the thicker oxides formed on films with lower density. Magnetic hysteresis measurements were made with a vibrating sample magnetometer. Below 1000 Å, porosity and surface oxidation result in reductions up to 25% in the saturation magnetization. An anomalous peak in coercivity at film thicknesses of 300-500 Å was observed, which can be explained by the change in domain wall type.