Tunable magnetic and electrical properties of polycrystalline and epitaxial Ni_xFe_3-xO₄ thin films prepared by reactive co-sputtering

Polycrystalline and epitaxial Ni_xFe_3-xO4 (0 ≤ x ≤ 1.03) thin films were fabricated by reactively co-sputtering Fe and Ni targets in a mixed Ar + O₂ atmosphere, and the structure, magnetic and magnetotransport properties were investigated systematically. The saturation magnetization and resistivity can be tuned over a wide range. The room-temperature saturation magnetization for the polycrystalline thin films decreases linearly with x from 440 to 230 emu cm^-3, due to Ni substitution. For the epitaxial thin films, the saturation magnetization and the resistivity can be tuned in the range 195-340 emu cm^-3 and 10 ^-4-10^-2 Ω m by Ni substitution and the introduction of Fe vacancies, because both Ni substitution and Fe vacancies can influence the charge carrier density and the double exchange on the B sublattice.