MAGNETIC-PROPERTIES OF GAMMA-FE2O3 NANOPARTICLES OBTAINED BY VAPORIZATION CONDENSATION IN A SOLAR FURNACE

The magnetic properties of gamma-Fe2O3 nanoparticles synthesized by va porization condensation in a solar image furnace have been studied usi ng both magnetic measurements and Mossbauer spectroscopy. The mean siz e of the particles turns out to be easily controlled by changing the p ressure conditions in the growth chamber. The particles exhibit superp aramagnetic behavior at room temperature. Magnetic measurements show t he appearance of magnetic hysteresis in the low-temperature range and from the evolution with temperature of the ferromagnetic ratio, M(R)/M (S), we have determined the distribution of the blocking temperatures for the smallest particles that is fitted to a log-normal distribution leading to a mean blocking temperature [T-B]=38+/-15 K. The size dist ribution of the magnetic unit is also determined from this fitting, as well as from the Mossbauer spectra, obtaining a mean particle volume of about 3.5X10(5) Angstrom(3). (C) 1996 American Institute of Physics .