Magnetic properties of the novel nanocomposite (Zn0.15Ni0.85Fe2O4)0.15/(SiO2)0.85 at room temperature

The value of the effective magnetic anisotropy constant of the ferrimagnetic nanoparticles Zn0.15Ni0.85Fe2O4 embedded in a SiO2 silica matrix, determined through ferromagnetic resonance (FMR), is much higher than the magnetocrystalline anisotropy constant. The higher value of the anisotropy constant is due to the existence of surface anisotropy. However, even if the magnetic anisotropy is high, the ferrimagnetic nanoparticles with a 15% concentration, which are isolated in a SiO2 matrix, display a superparamagnetic (SPM) behavior at room temperature and at a frequency of the magnetization field equal to 50 Hz. The FMR spectrum of the novel nanocomposite (Zn0.15Ni0.85Fe2O4)0.15/(SiO2)0.85, recorded at room temperature and a frequency of 9.060 GHz, is observed at a resonance field (B0r) of 0.2285 T, which is substantially lower than the field corresponding to free electron resonance (ESR) (0.3236 T). Apart from the line corresponding to the resonance of the nanoparticle system, the spectrum also contains an additional weaker line, identified for a resonance field of ∼0.12 T, which is appreciably lower than B0r. This line was attributed to magnetic ions complex that is in a disordered structure in the layer that has an average thickness of 1.4 nm, this layer being situated on the surface of the Zn0.15Ni0.85Fe2O4 nanoparticles that have a mean magnetic diameter of 8.9 nm.