MAGNETOTRANSPORT AND MAGNETISM IN GRANULAR EUS-CO AND EUS-AG NANOCOMPOSITES PREPARED BY MECHANICAL ALLOYING

Magnetic and magnetotransport properties have been studied in nanocomp osites (EuS)-Co and (EuS)-Ag prepared by mechanical alloying. For (EuS )(70)Co-30, the large negative magnetoresistance (similar to-50%) foun d at 20 K,just above the Curie temperature (T-c) of EuS, arises from t he suppression of spin fluctuation in EuS. Below T-c, the positive mag netoresistance (similar to 15%), which is uncharacteristic of ferromag netic semiconductors, is probably due to defect-induced magnetic fluct uation. On the other hand, (EuS)(70)Ag-30, where nonmagnetic silver re places cobalt, exhibits negative magnetoresistance below T-c, which is possibly related to the spin dependent scattering commonly seen in GM R materials. While (EuS)(70)Co-30 shows semiconducting conductivity, ( EuS)(70)Ag-30 is metallic. Reentrant spin glass behavior has been obse rved in EuS-Ag system, where the rise of antiferromagnetic coupling is due to the defects and disorder caused by mechanical milling.