Cation ratio and oxygen defects for engineering the magnetic transition of monodisperse nonstoichiometric zinc ferrite nanoparticles

Monodisperse nonstoichiometric zinc ferrite nanoparticles with a tunable size of 4.1–32.2 nm are fabricated via thermal decomposition. An extrinsic impurity phase the ZnO component is present in <10 nm, but this can be eliminated after air annealing treatment. The atom ratio Zn/Fe and concentration oxygen vacancies decrease as particle increases, causing magnetic transition from superparamagnetism to ferromagnetism. X-ray circular dichroism spectra reveal that spin moments Fe3+ reduced, orbital frozen increasing Zn/Fe. Therefore, saturation magnetization decreases. magnetizations all treatment, suggesting considerably influence properties. treatment minimize number defects, which trigger some Fe3+-OV-Fe3+ ferrimagnetic couplings transfer into Fe3+-O2−-Fe3+ antiferromagnetic couplings. This work provides new insights regarding performance spinel ferrites by tuning stoichiometric defects.