Size control of nanocrystalline magnetite thin films containing a small amount of Ge

This study investigated the preparation and particle size control of nanocrystalline magnetite (Fe3O4) containing a small amount of Ge. Thin films were prepared by radio-frequency sputtering with a composite target of Ge chips set on a Fe3O4 compound target in a mixed atmosphere of Ar and O2. X-ray diffraction revealed that the diffraction peak of magnetite gradually broadened as the oxygen ratio increased, with the mean grain size ranging from 26 to 2 nm. Transmission electron microscopy also revealed that the magnetite structurally changed from polycrystalline single phase to isolated granular nanocrystals. Magnetization at 8 × 105 A/m was monotonically reduced from 0.32 to 0.04 T, and coercivity was monotonically reduced from 4.2 × 104 to 2.1 × 103 A/m with increasing the oxygen ratio from 0 to 0.4%.