Highly spin-polarized current in Co-substituted Fe3O4 epitaxial thin films at room temperature

Epitaxial thin films of cobalt ferrite CoxFe3−xO4 (x = 0.0, 0.5, and 1.0) were fabricated on α-Al2O3 (001) substrates using pulsed laser deposition. It was found that the coercive force of the cobalt ferrite films could be tuned by changing the Co content. The films prepared under low oxygen pressure (1.0 × 10−6 Pa) showed semiconducting behavior even for x = 1.0. X-ray photoelectron spectroscopy revealed that the Co ions were 2+ for all compositions. On the other hand, it was found that the Fe ions were in the Fe2+/Fe3+ valence state, which may cause small-polaron hopping among the Fe-3d electrons in the films. An anomalous Hall effect was observed in the Co0.5Fe2.5O4 film even at 300 K, suggesting that carriers in the films were highly spin-polarized at room temperature.