Magnetoresistance of a (gamma-Fe2O3)(80)Ag-20 nanocomposite prepared in reverse micelles

The magnetic and transport properties of a (gamma-Fe2O3)(80)Ag-20 nanocompo site, prepared by a reverse micelle technique, have been studied. gamma-Fe2 O3 nanoparticles and Ag particles were individually synthesized in reverse micelles. The nanocomposite material was then prepared by mixing the two di fferent particles in a gamma-Fe2O3/Ag molar ratio 80/20. The morphology of the nanoparticles was examined with transmission electron microscopy. Mossb auer spectra revealed no obvious presence of any divalent iron. Zero field cooled and field cooled magnetic susceptibilities indicated a blocking temp erature of about 40 K. Negative magnetoresistance was observed resembling t hat in ball milled gamma-Fe2O3/Ag nanocomposites. However, the magnitude of the negative magnetoresistance is smaller and is similar to 2.2% at 220 K and 9 T. Two possible mechanisms, spin-dependent hopping and tunneling acro ss magnetic barriers, are discussed. (C) 2000 American Institute of Physics . [S0021-8979(00)47208-7].