Magnetic and transport properties of magnetite thin films

Magnetite (Fe3O4) films were prepared by DC reactive magnetron sputtering at various oxygen partial pressures with the ratio γ of oxygen to argon changing from 0.50:50 to 0.70:50 at room temperature, and then the Fe3O4 films were annealed at 480 °C for 80 min. The properties of the films were studied by X-ray diffraction, scanning electron microscopy, magnetic hysteresis loops, magnetoresistance (MR), etc. The results showed when γ increased, resistivity of magnetite films were increased exponentially, and only these magnetite films of γ>0.60:50 showed MR effects. After annealing, the resistivity decreased about one order; and all magnetite films showed MR effects. The Verwey transition of the magnetite films was confirmed by MR-T curves. XRD and SEM showed that the films were composed of Fe3O4 nanoparticles with highly preferential orientation and the best conditions for high-quality magnetite films were γ=0.65:50 and 0.675:50. The magnetic transport properties of the films infer that strong coupling between Fe3O4 nanoparticles originated from RKKY exchange interaction and dipolar interaction, this made the films differ from metallic granular ones and higher-order terms of (M/Ms)2, such as (M/Ms)4 and (M/Ms)6, should be added to the fitting functions of the MR-(M/Ms) curves.