THE MAGNETIC-BEHAVIOR OF FE2O3-BI2O3-ZNO FILMS

The observation of superparamagnetism is reported in thin films of 0.5 Fe(2)O(3)-0.1Bi(2)O(3)-0.4ZnO sputtered at high temperatures. The samp les were deposited in a mixed oxygen-argon atmosphere at substrate tem peratures T-s = 325-525 K. Films are X-ray amorphous and paramagnetic for T-s less than or equal to 475 K. For T-s = 525 K, 50 nm microcryst als of an unidentified phase are detected by X-ray diffraction (XRD). Magnetic measurements were done on this film for static fields as high as 30 kG and temperatures over the range 5-300 K. Curves of magnetiza tion versus temperature for field-cooled and zero-field-cooled conditi ons separate at a specific temperature T-f. Below T-f, hysteresis and remanence are observed in the static field dependence of the magnetiza tion. The superparamagnetic behavior is attributed to clusters with a mean diameter of 7 nm which are not identified by XRD.