Exploring the structural, Mössbauer and dielectric properties of Co2+ incorporated Mg0.5Zn0.5−xCoxFe2O4 nanocrystalline ferrite

The nanocrystalline Mg0.5Zn0.5−xCoxFe2O4 (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) ferrites have been synthesized by sol-gel auto ignition method. Rietveld refinement of X-ray diffraction (XRD) patterns of all concentrations show mixed cubic spinel structure. The lattice constant values infer decreasing trend from 8.420 to 8.392 Å with the substitution of Co2+. The crystallite size calculated from Scherer formula lies in the range between 28 and 37 nm which confirms the nanocrystalline nature of synthesized samples. In order to study the morphology and phase structure of the synthesized samples, samples were examined by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) confirmed the homogeneous and well defined surface morphology of the synthesized samples. The elemental analysis as obtained from energy dispersive X-ray (EDAX) is in close agreement with the expected composition from the stoichiometry of reactant solutions used. The valence states of the Co2+ ions have been confirmed with the help of X-ray photoelectron spectroscopy. Magnetization results obtained from the vibrating sample magnetometer (VSM) confirm that the substitution of Co2+ for Zn2+ caused an increase in the saturation magnetization and coercivity. The dependence of Mössbauer parameters, viz., line width, isomer shift, quadrupole splitting and hyperfine magnetic field on Co2+ substitution have been analyzed. Cation distribution estimated from XRD and Mössbauer spectroscopy are in good agreement with each other. The frequency dependent dielectric properties were studied by measuring dielectric constant (ε׳) and ac conductivity (σac) at 300 K in the frequency range of 50 Hz-5 MHz. The highest value for ε׳ and σac is observed for x=0.5.