Abstract

Nanoparticles of Fe_2O_3 with a mean particle size of 4-30 nm have been prepared by a pulsed wire evaporation method, and its structural and magnetic properties were studied by SQUID magnetometer and Mossbauer spectroscopy. From the main peak intensity of XRD and absorption rate of Mossbauer spectrum, the amounts of gamma-Fe_2O_3 and alpha-Fe_2O_3 in as-prepared sample are about 70% and 30%, respectively. The coercivity (53 Oe) and the saturation magnetization (14 emu/g) are about 20% of those of the bulk gamma-Fe_2O_3. The low value of coercivity and saturation magnetization indicate that the gamma-Fe_2O_3 phase nearly shows the spin glass-like behavior. Analysis of the set of Mossbauer spectrum indicates a distribution of magnetic hyperfine fields due to the particle size distribution yielding 20 nm of average particle size. The magnetic hyperfine parameters are consistent with values reported of bulk gamma-Fe_2O_3 and alpha-Fe_2O_3. A quadrupole line on the center of spectrum represents of superparamagnetic phase of gamma-Fe_2O_3 with a mean particle size of 7 nm or below.

• Keywords: Fe_2O_3;Mossbauer spectrum;Superparamagnetic;