Study on the influence of annealing temperature and ferrite content on the structural and magnetic properties of x(NiFe_2O_4)/(100-x)SiO_2 nanocomposites

摘要

Magnetic nanocomposites of nickel ferrite nanoparticles uniformly dispersed in the silica matrix have been synthesized successfully by a sol-gel process using tetraethylorthosilicate (TEOS) and metallic nitrates as precursors. In addition, the influence of the annealing temperatures, varying from 400 to 900°C, and NiFe_2O_4 contents, x(NiFe_2O_4)/(l00-x)SiO_2 (10 ≤x ≤ 60 wt.%), on the structural and magnetic properties of the nanocomposite samples have been investigated. The studies carried out using XRD, FT-IR, TEM, STA (TG-DTG-DTA) and VSM techniques. The results indicated that the structural and mag-netic properties of the samples showed great dependence on the variation of the particle size caused by the annealing temperature and NiFe_2O_4 content. The crystallization, saturation magnetization M_s and remenant magnetization M_r increased as the annealing temperature and NiFe_2O_4 content increase. But the variation of coercivity H_c was not in accordance with that of M_s and M_r, indicating that H_c is not determined only by the size of NiFe_2O_4 nanoparticles. TEM images showed spherical nanoparticles homogeneously dispersed in the silica network and were uniform in both morphology and particle size distribution with sizes of 10-15nm. The results showed that the well-established silica network pro-vided nucleation locations for NiFe_2O_4 nanoparticles to confinement the coarsening and aggregation of nanoparticles. The synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of nickel ferrite even more versatile.