OBSERVATION OF SUPERPARAMAGNETISM IN RF-SPUTTERED FILMS OF ZINC FERRITE

Structural and magnetic properties of rf-sputtered zinc ferrite, ZnFe2O4, have been studied using X-ray diffraction, susceptibility, and high-field magnetization measurement techniques. Films prepared by radio-frequency sputtering in argon, oxygen or mixed argon-oxygen atmospheres contain a microcrystalline phase, most likely nonstoichiometric wustite Fe2O. Argon-sputtered samples show spin freezing below 60 K. For samples deposited in pure or partial oxygen atmospheres, data on temperature and field dependence of susceptibility and magnetization provide strong evidence for a superparamagnetic character. Anomalous variations are observed in the ferromagnetic resonance line width at temperatures close to the spin freezing temperature. Ferrimagnetically ordered clusters are suggested to cause the superparamagnetic behavior.