LAUSR

Abstract The surfactant coated cobalt ferrite (CoFe2O4) samples were synthesized at different temperatures by different synthesis routes. The oleic acid (OA) coated cobalt ferrite sample synthesized at 80 °C by co-precipitation route while, sodium dodecyl sulfate (SDS) and cetyl-trimethyl ammonium-bromide (CTAB) cobalt ferrite samples were synthesized at 140 °C and 180 °C by hydrothermal process respectively. The average crystallite size of 14.9 ± 0.2 nm, 19.1 ± 0.3 nm and 21.3 ± 0.2 nm at higher intensity peak (311) of X-ray diffraction pattern (XRD) for CF-OA, CF-SDS, and CF-CTAB sample respectively were estimated using Lorentz fitting profile of experimental data. Transmission electron microscopy (TEM) images show randomly oriented nanoparticles of the irregular shape of CF-OA sample, globular shape for CF-SDS and rhomboidal shape of CF-CTAB sample respectively. The average particle size of 15.7, 22.7 and 30.1 nm for CF-OA, CF-SDS and CF-CTAB sample were estimated using TEM analysis. FTIR spectra of all samples confirmed the coating of surfactant on the surface of cobalt ferrite nanoparticles. The temperature dependence electron paramagnetic resonance (EPR) spectra of all samples in the non-magnetic matrix were measured in the temperature range (100 K–300 K). The linewidth and g-factor from their EPR signal were increased significantly with increase in particle size of the sample. The spin-spin relaxation time T2 was estimated from linewidth of EPR signal of the sample. The spin-spin relaxation time T2 decreased with increase in linewidth as an increase in particle size of the sample. The linewidth of EPR signal was decided by dipolar interactions between nanoparticles and super-exchange interaction between metal cations at tetrahedral and octahedral sites of the CoFe2O4 sample.