The metamorphosis of heterometallic trinuclear antiferromagnetic complexes into nano-sized superparamagnetic spinels

Thermal decomposition of the trinuclear heterometallic oxoacetates [Fe2M(μ3-O)(CH3COO)6(H2O)3] has been used as a single-precursor method for synthesis of the spinel-structured ternary oxides MFe2O4 (M = MnII, CoII, and NiII). This facile process occurring at 320 °C results in the formation of nanocrystalline (7-20 nm) highly pure stoichiometric ferrites in quantitative yield. The magnetic properties of these nanoparticulate ferrites were studied in the 10-300 K temperature range, revealing superparamagnetic behavior for the Ni and Mn particles and ferrimagnetic behavior for the Co ones at room temperature. Their blocking temperatures follow the order: CoFe2O4 > MnFe2O4 > NiFe2O4.