Influence of annealing atmosphere on the magnetic properties of SiO_2/Fe/SiO_2 sandwiched nanocomposite films

摘要

The magnetic properties of SiO_2/Fe/SiO_2 nanocomposite films are studied by magnetic force microscopy and vibrating sample magnetometer. The films were fabricated by alternately depositing SiO_2, Fe, and SiO_2 on Si substrates with magnetron sputtering followed by thermal annealing. It is found that the annealing atmosphere significantly influences the sample structure, composition, and magnetic properties. The samples annealed in forming gas show much better magnetic properties than those annealed in vacuum and in N_2. The saturation magnetization can reach 200 emu/g, fairly close to the value of bulk Fe, and the coercivity can reach 400 Oe, much higher than 10 Oe of the bulk Fe. X-ray photoelectron spectroscopic depth profile measurement was carried out to study the mechanism of the strong influence of annealing atmosphere. For the samples annealed in forming gas, Fe nanoparticles are mildly oxidized, forming thin shells of Fe_2O_3 surrounding them, which is beneficial for maintaining the ferromagnetic behavior and enhancing the coercivity of nanoparticles.