Strained CoFe2O4-amorphous SiO2 nanocomposites: Evaluation of structural and magnetic properties

Abstract

Strained CoFe2O4 nanoparticles were dispersed in a SiO2 matrix prepared by the co-precipitation method. Rietveld refinement is performed to estimate structural parameters and distribution of cations at tetrahedral and octahedral sites respectively. W-H-ISM and W-H-ASM models were applied to evaluate lattice strain, crystallite size and lattice deformation stress. The decrease in coercivity and saturation magnetization observed with increased temperature and SiO2 content. Reduction in magnetization is attributed to the increased number of disordered surface spins with enhanced strain and reduced effective and surface anisotropy. The blocking temperature (TB)is evaluated as 347.9 K for CF, 349.2 K for 5%SiCF, 352.1 K for 10%SiCF and 353.4 K for 15%SiCF nanoparticles respectively. The Higher value of μSP(μB) is observed for CF nanoparticles at 350 K, represented in temperature and magnetic field dependent superparamagnetic moment (μSP(μB)) curves. A new dependency observed between variations of μSP(μB) with strain values as enhanced μSP(μB)is observed with increasing strain values for the higher concentration of SiO2. An enhancement in the saturation magnetic field (HHT) with increasing temperature confirms the necessity of a higher magnetic field for reaching saturation values. A new relation is examined for variation of Ms and μSP(μB) with strain values from 5 K to 350 K.