We have investigated the magnetic properties of Fe3O4 thin films with
thicknesses below 1000 Angstrom. Previous reports had indicated an ano
malous decrease in the saturation magnetization of Fe3O4 films with th
icknesses below 700 Angstrom. The films were prepared by reactive rf m
agnetron sputtering and effects of film thickness, oxygen flow rate, a
nd substrate temperature were examined. A region of acceptable magneti
c properties, which do not vary with film thickness, for Fe3O4 films h
as been found at both RT and 400 degrees C. Within the processing regi
on for single-phase Fe3O4, the magnetic properties did not vary signif
icantly with oxygen partial pressure but did change with substrate tem
perature. The RT films are characterized by low saturation magnetizati
on, 250 emu/cm(3) and modest coercivity, 250 Oe. The films at 400 degr
ees 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 deg
ree of cation disorder; the higher coercivity at 400 degrees C is anom
alous. 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.