Magnetic properties of gamma-Fe2O3 nanoparticles obtained by vaporization condensation in a solar furnace

The magnetic properties of gamma-Fe2O3 nanoparticles synthesized by vaporization condensation in a solar image furnace have been studied using both magnetic measurements and Mossbauer spectroscopy. The mean size of the particles turns out to be easily controlled by changing the pressure conditions in the growth chamber. The particles exhibit superparamagnetic behavior at room temperature. Magnetic measurements show the 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 distribution 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.