Effects of thickness and high magnetic field on the microstructure and magnetic properties of FeNi-SiO2 nanoparticle composite films

In order to obtain uniform distribution of nanoparticles with various thicknesses, FeNi-SiO2 nanoparticle composite films have been fabricated by co-evaporation using molecular beam vapor deposition method. Meanwhile, insitu high magnetic field is used to tune the growth of nanoparticles. The films are formed with the FeNi nanoparticles embedded in dielectric SiO2. The size of nanoparticles is observed to increase with the film thickness, however, diameter of the nanoparticles remains in the range of 3-5 nm and distributes uniformly in the film whose thicknesses is within the range of 15-100 nm. High magnetic field is found to promote the aggregation of FeNi nanoparticles and helps diffusing through the SiO2 matrix to the film boundaries. This leads to a refinement of nanoparticle size. Magnetic anisotropy of the 0 T films due to the existence of two phases and the shape anisotropy does not change to isotropy with applying high magnetic field. Coercivity still remains at about 9 Oe for all the films. Saturation magnetization is increased with increasing thickness and applying high magnetic field. This means that high magnetic field has a strong effect on the improvement of the magnetization saturation and, at the same time, the refinement of nanoparticle sizes. (C) 2016 Elsevier Ltd. All rights reserved.