Unusual occupancy of more Fe3+ ions at A-site and enhanced metallic magnetization in nano Mg0.5Zn0.5Fe2O4

• Unique observation of A-site occupancy of Fe 3+ instead of conventional B site occupancy is observed.
• Increased charge carriers at the grain boundary due to nano nature are responsible for the unusual metalicity.
• The different between the actual and predicted Fe3+ ions are accommodated in the grain boundaries.
• Experimental magnetization is found to be greater than the Mossbauer calculated magnetic moment added to surface contribution.
• Enhanced magnetization [(35.56 emu/g)+30% (10 emu/g)] can be explained by A-O-B Zeners’ double exchange interaction.

Unusual Fe3+ occupancy at A-site, giving rise to saturation magnetization (Ms) close to bulk accompanied by reduced coercivity at increased particle size has been found in co-precipitated Magnesium Zinc ferrite (Mg0.5Zn0.5Fe2O4) by varying precipitation temperature. Cation distribution independent enhanced magnetization is observed in the superparamagnetic regime with existence of only Fe3+ in A site from Mossbauer studies. Owing to increased grain boundary volume, localization induced metalicity has been found from the electrical characterization. Anomalous changes like very low dielectric constant and high resistance with increasing temperature in the impedance analysis has been found. The vanishing of dielectric constant is a consequence of more Fe at either A or B site which further confirms the Mossbauer result of increased Fe3+ content at A-site. Uniquely, increased Fe3+ ions at A site is independently confirmed from the electrical and magnetic characterization. Highly intense Raman A1g mode occurring at high energy of 695 cm−1 is mainly ascribed to the motion of Fe3+ in the tetrahedral AO4 complex and the particle size induced red shift has also been found.