Size and compositionally controlled manganese ferrite nanoparticles with enhanced magnetization

A facile solvothermal approach was used to synthesize stable, superparamagnetic manganese ferrite nanoparticles with relatively small sizes (<10 nm) and enhanced magnetic features. Tetraethylene glycol has been used in all the syntheses as a biocompatible and stabilizing agent. By varying the oxidation state of manganese precursor, Mn(acac)₂ to Mn(acac)₃, different sizes, 8 and 5 nm, of MnFe₂O₄ nanoparticles were obtained respectively, while by tailoring the synthetic conditions iron-rich Mn_0.77Fe_2.23O₄ nanoparticles have been isolated with identical sizes and enhanced saturation magnetization. The magnetization values increased from 58.2 to 68.3 Am²/kg and from 53.3 to 60.2 Am²/kg for the nanoparticles of 8 and 5 nm, respectively. Blocking temperature (T _B), ranging from 80 to 180 K, and anisotropy constant (K _eff), ranging from 1.5 × 10⁵ to 4.9 × 10⁵ J/m³, were found higher for the iron-rich samples and associated with size and composition effects.