Effect of substrate temperature on structure and magnetic properties of Fe/C granular multilayers

[Fe (3 nm)/C (3 nm)]₁₀ granular multilayers were synthesized by alternately depositing iron and carbon at different substrate temperatures using magnetic sputtering. The effects of substrate temperature on the microstructure, surface morphology and magnetic properties were investigated using X-ray diffraction, Raman spectroscopy, atomic force microscopy, transmission electron microscopy, magnetic force microscopy and superconducting quantum interference device magnetometer. Results show that the Fe/C granular multilayers films exhibit amorphous-like structure and the crystalline Fe particles are dispersed in an amorphous C matrix, namely, the Fe/C granular multilayers consisting of successive planes of nanosized Fe grains are separated by amorphous C along the growth direction. With the increase of substrate temperature from room temperature to 350 °C, Fe grain sizes increase from ~8.42 to ~9.59 nm, and Fe and C phases are separated completely at 350 °C. Magnetic measurements reveal that the coercivity and saturation magnetization of the Fe/C granular multilayers are strongly dependent on substrate temperature. The coercivity increases with the increase of substrate temperature, while the saturation magnetization decreases. It suggests that the enhanced coercivity can be attributed to the weakened inter-grain interaction because of the phase segregation and the increase in grain size, and the reduction of saturation magnetization is due to the diffusion of the C atoms to the surfaces of Fe particles. The magnetic domain percolation behavior cannot be observed in Fe/C granular multilayers since the Fe volume fraction is less than percolation threshold in our experiment.