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.