Magnetic and transport properties of magnetite thin films

Abstract

Magnetite (Fe 3O 4) 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 Fe 3O 4 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 Fe 3O 4 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 Fe 3O 4 nanoparticles originated from RKKY exchange interaction and dipolar interaction, this made the films differ from metallic granular ones and higher-order terms of (M/M s) 2, such as (M/M s) 4 and (M/M s) 6, should be added to the fitting functions of the MR–(M/M s) curves.