Enhanced magnetization in cubic ferrimagnetic CuFe₂O₄nanoparticles synthesized from a citrate precursor: the role of Fe²⁺

Abstract

We report a simple liquid dehydration route involving citrate precursors to synthesize single-phase ferrimagnetic copper ferrite (CuFe2O4) nanoparticles with a cubic crystal structure. Superparamagnetism was exhibited by 5 nm CuFe2O4 particles while ferrimagnetism prevailed at 11 nm and above. The cubic CuFe2O4 samples grown under specific conditions show a systematic enhancement in the saturation magnetization. Both quantitative chemical analysis and the unit cell volume data indicate that samples with larger magnetization contain a higher fraction of Fe2+ ions in place of Fe3+. We provide a plausible model for the cation distribution among the available tetrahedral and octahedral sites that quantitatively explains the observed enhancement in the saturation magnetization. This appears to be the first attempt to increase the magnetization by controlling the Fe2+ concentration.