Magnetic properties of uniform gamma-Fe2O3 nanoparticles smaller than 5 nmprepared by laser pyrolysis

gamma-Fe2O3 spherical particles with diameters between 5 and 3.5 nm-very un iform in size-have been prepared by laser pyrolysis of iron pentacarbonyl. The infrared spectra of the samples showed features that indicated differen t degrees of crystallinity according to the preparation conditions. Low sat uration magnetization values (approximate to 10 emu/g) and very high coerci vities at low temperature (3000 Oe) have been found for the gamma-Fe2O3 nan oparticles with the smaller particle size and the highest structural disord er. To explain the magnetic properties, it was necessary to consider additi onal anisotropies caused by the increase in surface and structural disorder as the particle size decreased.