MAGNETIC-PROPERTIES OF REACTIVELY SPUTTERED FE1-XO AND FE3O4 THIN-FILMS

We have investigated the magnetic properties of Fe3O4 thin films with thicknesses below 1000 Angstrom. Previous reports had indicated an anomalous decrease in the saturation magnetization of Fe3O4 films with thicknesses below 700 Angstrom. The films were prepared by reactive rf magnetron sputtering and effects of film thickness, oxygen flow rate, and substrate temperature were examined. A region of acceptable magnetic properties, which do not vary with film thickness, for Fe3O4 films has been found at both RT and 400 degrees C. Within the processing region for single-phase Fe3O4, the magnetic properties did not vary significantly with oxygen partial pressure but did change with substrate temperature. The RT films are characterized by low saturation magnetization, 250 emu/cm(3) and modest coercivity, 250 Oe. The films at 400 degrees C have a higher saturation magnetization, 330 emu/cm(3), but also a higher coercivity, 450 Oe. The increased saturation magnetization at higher temperature results from the higher film density and lower degree of cation disorder; the higher coercivity at 400 degrees C is anomalous. In addition, at RT we have discovered a processing region where ferrimagnetic wustite, Fe1-xO, is formed. The Fe1-xO films have good soft magnetic properties and warrant further study.