Structural and magnetic properties of single domain CoFe2O4 magnetic nanoparticles dispersed in SiO2 matrix

Abstract

Uniformly dispersed CoFe2O4 nanoparticles in SiO2 matrix have been synthesized in two-step process by a co-precipitation route at lower temperature (70 °C). Phase purity and average crystallite size of cobalt ferrite (CFO) and CoFe2O4 nanoparticles dispersed in SiO2 matrix (Si-CFO) have been evaluated to be 17.6 nm and 15.2 nm respectively. Bond edges and bond lengths were evaluated from Rietveld refinment confirms the existence of compressed and tensile strain in CFO and Si-CFO nanoparticles. The average particle sizes evaluated from transmission electron microscope (TEM) were found to be 16 and 17.3 nm respectively. Functional groups present in CFO and Si-CFO nanoparticles were investigated from Fourier transform infrared spectra (FTIR). Magnetic properties were investigated by vibrating sample magnetometry (VSM). Lower saturation magnetization (25.6) with enhanced coercivity (977) at room temperature has been observed for Si-CFO nanoparticles and attributed to the increased number of disordered surface spins with reduced effective magnetic anisotropy, enhanced stress and surface anisotropy. Strain in CFO and Si-CFO nanoparticles have been evaluated from magnetic measurements and corroborate well with the strain evaluated from Williamson-Hall-Isotropic strain model (W-H-ISM) and Williamson-Hall-Anisotropic strain model (W-H-ASM). Effect of specific saturation magnetization specific surface area and dead magnetic layer thickness on magnetic properties of pristine CFO and Si-CFO nanoparticles have been investigated. The enhanced specific surface area and dead magnetic layer thickness resulted in increased strain in Si-CFO with reduced saturation magnetization. The dead layer thickness is evaluated to be 1.34 nm and 1.96 nm for CFO and Si-CFO nanoparticles respectively.