Nickel Ferrite Thin Films: Microstructures and Magnetic Properties

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Abstract
Thin films of nickel ferrite (NiFe2O4) have been prepared by a reactive‐sputtering technique using an iron‐nickel alloy as the cathode and oxygen‐argon mixtures as the reactive gas. Electron microscopy and electron‐diffraction studies indicate that films deposited on substrates at temperatures below 0°C are noncrystalline whereas films deposited at higher temperatures are polycrystalline, the size of the crystallites increasing as the temperature is increased. Measurements of electrical conductivity and magnetic susceptibility have been made on films prepared at various temperatures, and the results are interpreted in terms of film microstructure. In particular, the noncrystalline films show paramagnetic behavior, and the micropolycrystalline films show superparamagnetic behavior; ferrimagnetism is only found in films having a grain size greater than 150 Å and prepared at 400°C and above.