Cation effect on the magnetic and magnetotransport properties of CoxFe3−xO4 films: An experimental and first-principles study

The spin polarization is a key quantity for spintronics . Spinel-type multiple oxides such as Fe₃O₄ or CoFe₂O₄, are commonly used in the spintronic devices to generate highly spin-polarized electrons, either for spin injection into semiconductors or for magnetoresistive effects . The inverse spinel structure is a cubic crystal system, with oxide anions arranged in a cubic close-packed lattice and metal cations tetragonally or octahedrally surrounded by the oxygen. For Fe₃O₄ and CoFe₂O₄, Fe³⁺ ions occupy the tetrahedral sites and half of the octahedral sites, whereas Fe²⁺ and Co²⁺ ions are located at the remaining octahedral sites . Because of the different cations at the remaining octahedral sites, Fe₃O₄ and CoFe₂O₄ exhibit series of cation-specific properties, such as Fe₃O₄ is a half-metal semiconductor while CoFe₂O₄ is an insulator at room temperature . In our previous studies on multiferroic composite Fe₃O₄/BiFeO₃ [1, 2], we found that the cations at the interface strongly influence the magnetoelectric of the multiferroic composites . Previous studies always characterized the magnetic properties of Co_xFe_3-xO₄ spinels [3, 4] . To date, only a limited number of papers have reported the electrical transport properties of Co_xFe_3-xO₄. However, a fundamental understanding of the microstructure, magnetic and electrical transport properties of the Co_xFe_3-xO₄ is crucial. The purpose of the present study is to give a systematic investigation of the cation-specific properties of the Co_xFe_3-xO₄ spinel .