Phase decomposition and related structural and magnetic properties of iron-cobaltite thin films

Iron-cobaltite (Co3-xFexO4) thin films exhibited a spinodal decomposition (SD) into two distinct cubic spinel phases as the Fe composition was varied near x = 1. Polycrystalline films of spinel oxides (x ≤ 2.0) were prepared on Si(100) substrates by using a sol-gel deposition, followed by subsequent air-annealing at 800 .deg. C. X-ray diffraction results revealed that the two coexisting spinel phases (I and II) in the SD region had different lattice constants by about 2% (aI < aII). Phases I and II were found to have Fe compositions of about 0.5 and 1.5, respectively. The X-ray photoelectron spectroscopy investigation indicated that the Fe ions mainly had a valence of +3 for all Fe compositions. Magnetic hysteresis measurements revealed that phase II had a magnetization strength larger than that of phase I by about 20 times. These experimental results imply specific site preference of Co2+ ions for the two phases of the SD region: tetrahedral sites for phase I and octahedral sites for phase II.