Investigation of significant magnetic transformation for hydrogenated ZnFe2O4 nanoparticles.

This paper firstly studied an obvious magnetic transformation from paramagnetism to superparamagnetism in hydrogenated ZnFe2O4 nanoparticles. The zinc ferrite nanoparticles were successfully prepared by a simple solid-state reaction followed by a ball milling method. Moderate thermal treatments under hydrogen atmosphere were carried out, and a phenomenon was observed that the magnetic behavior of zinc ferrite nanoparticles transformed from paramagnetism to superparamagnetism. Various characterizations were carried out to confirm the creation of the hydrogen doping induced defects under post-treatments, which may be crucial for the magnetic transformation. By studying the effect of the defects caused by hydrogenation on the magnetization, we found that the oxygen vacancies could alter the magnetic ordering of materials and therefore modulate the magnetic behaviors. In addition, the saturation magnetization decreased after reheating the hydrogenated Zn-ferrite samples in the air, which indicated that the oxygen vacancies and Fe2+ ions directly modulated the magnetization of the Zn-ferrite materials. Notably, the residual saturation magnetization was still higher than raw Zn-ferrite, indicating that the changes of cation distribution could also modulate the magnetization and certain changes were irreversible. [ABSTRACT FROM AUTHOR]