Effect of amorphous silica matrix on structural, magnetic, and dielectric properties of cobalt ferrite/silica nanocomposites

Abstract

Effect of amorphous silica (SiO2) matrix concentration on structural, magnetic, and dielectric properties of (CoFe2O4)1y/(SiO2)y nanocomposites with y (SiO2 concentration)=10, 30, 50 and 60% was studied in detail. CoFe2O4 nanoparticles dispersed in SiO2 matrix were prepared by using sol-gel method. X-ray diffraction (XRD) analysis revealed the spinel ferrite structure for all the samples. The average crystallite size was decreased with SiO2 concentration (y) due to large number of nucleation sites formed by SiO2 matrix during synthesis (for the formation of nanoparticles), which finally restricts the particle growth. Fourier transform infrared (FTIR) spectroscopy confirmed the formation of spinel ferrite and SiO2 matrix. Scanning electron microscopy (SEM) images showed that the particles are spherical in shape and less agglomerated. The magnetization was decreased on increasing the SiO2 concentration and is attributed to diminishing of the particle size with SiO2 concentration. Smaller nanoparticles exhibit lower magnetization as compared to larger nanoparticles due to disordered surface spins. Dielectric constant, loss tangent and imaginary part of dielectric constant all showed decreasing trend with increasing frequency due to inability of the space charge carriers to keep with the alternation electric field, while ac conductivity increases with increasing frequency. All dielectric parameters also showed dependency on SiO2 concentration and were decreased with increasing SiO2 concentration. The reduction of magnetic and dielectric properties is attributed to diminishing of crystallite size with increasing SiO2 matrix concentration. Therefore SiO2 matrix can be useful in controlling the nanoparticle size and dielectric as well as magnetic properties of the ferrite nanoparticles.