Effect of thermal-treatment on structural, mössbauer and magnetic properties of ZN-Nanoferrite

We report synthesis of spinel ZnFe2O4 ferrite by solution combustion method. Room temperature x-ray diffraction ‘XRD’; magnetic; 57Fe Mössbauer measurements were used to probe thermal treatment dependence of the structural, magnetic properties, and connection between them. Mössbauer spectroscopy was particularly used to identify the presence of magnetic/non−magnetic phases, their effect on magnetic properties. XRD confirms the formation of spinel phase, trace of α−Fe2O3 was also detected. Thermally treated samples show: i) substantial increase of grain diameter: 20.3 to 48.8 nm, presence of compressive−strain, ii) increase of inversion parameter: 0.20 to 0.65, iii) redistribution of Zn2+, Fe3+ ions on A, B site, therefore increasing the disorder, iv) strengthening of A−O−B, A−O−A, with simultaneous weakening of B−O−B superexchange interaction, v) increase of magnetic−dead−layer thickness, thus affecting magnetic properties. Coercivity variation with grain diameter suggests that the studied samples lie in the overlap region between single/multiple−domains. Non−zero canting angle suggests the applicability of Yafet−Kittel three sub lattice model. Magnetization behaviour is explained using core (ordered−spin)−shell (spin−canting) model. Mössbauer results confirm: a) the 3+ state of Fe ions, b) the presence of α−Fe2O3 phase, and being antiferromagnetic reduces the saturation magnetization. Thermal treatment assisted modification of line width range between 0.42 to 0.72 mm/s, is attributable to surface strain/domain pinning. Mössbauer spectra confirm the presence of two superparamagnetic doublets that are explained by core (lower quadrupole splitting) − shell (higher quadrupole splitting) model. XRD, magnetic measurements combined with Mössbauer spectrosopy, provide improved understanding on the effect of thermal treatments on magnetic properties.