Synthesis of nonstoichiometric zinc ferrite nanoparticles with extraordinary room temperature magnetism and their diverse applications

A series of nonstoichiometric zinc ferrite (Zn_dFe _3-dO₄) nanoparticles with Zn-dopant concentration d ranging from 0 to 0.5 was synthesized via thermal decomposition route employing oleic acid as surfactant. The zinc dopant concentration was controlled by the ratio of Zn/Fe precursors. High room temperature saturation magnetization of 110 emu g^-1 was obtained for large Zn ferrite particles (more than 100 nm) with nominal composition of Zn_0.468Fe_2.532O ₄. The origin of the extraordinary magnetic property was revealed as the Zn substitution of Fe atoms at the tetrahedral site (A site) in the spinel magnetite phase. It was found that the precursor/surfactant ratio was an important parameter for the control of the shape and size of as-synthesized Zn ferrite particles. The details were investigated through a series of experimental work. Size-dependent applications, such as radar absorption and magnetic fluid hyperthermia, were further studied. Both applications required magnetic particles with high saturation magnetization, hence our samples displayed advantages over Fe₃O₄ magnetite nanoparticles. Especially for magnetic fluid hyperthermia, 26 nm Zn ferrite nanoparticles coated by P-mPEG polymer showed superior biocompatibility and heating efficiency, implying the potential usefulness to in vivo cancer therapy.