OBSERVATION OF SUPERPARAMAGNETISM IN RF-SPUTTERED FILMS OF ZINC FERRITE

Structural and magnetic properties of rf-sputtered zinc ferrite, ZnFe2 O4, have been studied using X-ray diffraction, susceptibility, and hig h-field magnetization measurement techniques. Films prepared by radio- frequency sputtering in argon, oxygen or mixed argon-oxygen atmosphere s contain a microcrystalline phase, most likely nonstoichiometric wust ite Fe2O. Argon-sputtered samples show spin freezing below 60 K. For s amples deposited in pure or partial oxygen atmospheres, data on temper ature and field dependence of susceptibility and magnetization provide strong evidence for a superparamagnetic character. Anomalous variatio ns are observed in the ferromagnetic resonance line width at temperatu res close to the spin freezing temperature. Ferrimagnetically ordered clusters are suggested to cause the superparamagnetic behavior.