A comparative study on the structural, magnetic and dielectric properties of magnesium substituted cobalt ferrites

Abstract

The structural, morphological, vibrational, dielectric and magnetic properties of polycrystalline samples of Co 1- x Mg x Fe 2 O 4 ( x = 0.00, 0.02, 0.07, 0.12 and 0.30) acquired from sol-gel process has been reported. Structural studies from Rietveld refinement of XRD patterns verified the development of single-phase samples. Raman spectroscopy shows the presence of additional peaks at 620 cm −1 and 660 cm −1 confirming the mixed–spinel structure. With the increase in Mg 2+ substitution, the saturation magnetization decreases from 77.6 emu/g to 56.9 emu/g while the coercive field initially increases ( x < 0.07) and then decreases from 846 Oe to 742 Oe. Except for the x = 0.30 sample, the impedance spectroscopy shows two relaxation peaks in the rest of the samples. The contribution of electroactive regions such as grains, grain boundaries and electrode effect are identified by the comparative study of impedance and modulus spectroscopy. The Nyquist plots are modeled to equivalent circuits accordingly. The activation energy estimated from modulus spectroscopy and Nyquist plots is found to be comparable. The dielectric constants at 323 K are initially found to increase and then decrease. The ac conductivity is interpreted by considering Jonschers’ Power Law as well as Double Power Law and concluded that the small polaron hopping is responsible for electrical conductivity.