Determination of ferromagnetic, superparamagnetic and paramagnetic components of magnetization and the effect of magnesium substitution on structural, magnetic and hyperfine properties of zinc ferrite nanoparticles

Mg(x)Zn(1-x)Ee(2)O(4) nanoparticles (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0) were synthesized by auto combustion method. Structural refinement of the samples using Rietveld method revealed cubic spinel structure and showed migration of Fe3+ ions from octahedral to tetrahedral site with increase in magnesium concentration. TEM analysis showed that Mg doping has no significant influence on average particle size of the samples. The FTIR confirmed spinel structure and shift of v(1) and v(2) bands with magnesium concentration corroborated cation migration obtained from Rietveld analysis. The simultaneous presence of doublet and collapsed sextet in the Mossbauer spectra is attributed to superparamagnetic or paramagnetic and ferromagnetic particles respectively. The strength of the collapsed sextet increased with the magnesium concentration owing to the enhancement of A-B superexchange interaction. Saturation magnetization is found to be varied with magnesium concentration in accordance with Yafet-Kittel model. The superparamagnetic, ferromagnetic and paramagnetic phases in each sample were resolved by curve fitting the experimental M - H curves which confirm findings of our Mossbauer results. Also the contribution of these phases to saturation magnetization was estimated and the coexistence of different magnetic phases is attributed to distribution of particle size.