MOSSBAUER AND X-RAY-DIFFRACTION STUDIES OF HEAT-TREATED FE3O4 FINE PARTICLES

Samples of Fe3O4 fine particles heated at different temperatures have been studied using Mossbauer spectroscopy and X-ray diffraction. The fresh sample and that heated at 160 degrees C both show superparamagnetic behavior. However, the Mossbauer spectra of samples heated at higher temperatures are all magnetically split. The Mossbauer data with and without the application of similar to 0.4 T magnetic field perpendicular to the direction of propagation of the gamma-rays indicate a gradual conversion of Fe3O4 to gamma-Fe2O3 and then to alpha-Fe2O3 with increasing heating temperature, and a complete conversion to alpha-Fe2O3 in the sample heated at 550 degrees C. The observed increase in the B-hf With heating temperature is attributed to particle growth. Also, X-ray data indicate particle growth with increasing heating temperature, and partial transformation to alpha-Fe2O3 in the sample heated at 350 degrees C, and a total conversion in the sample heated at 550 degrees C.