Magnetotransport and antiferromagnetic coupling in nanocomposites EuS-Co

Nanocomposites (EuS)xCo100-x (x=30, 50 and 70) were prepared by mechanical alloying the powders of EuS and cobalt. X-ray diffraction analysis indicated that the average particle size of EuS was reduced to about 10 nm after 50 h of milling. These EuS nanoparticles were finely mixed with the metallic cobalt. Below the Curie temperature of EuS, its moments tended to couple antiferromagnetically with that of cobalt. This macroscopic ferrimagnetic behavior was best demonstrated in the magnetization versus temperature curve of (EuS)30Co70, where a rapid decrease in the magnetization below about 16 K (TC=16 K for EuS) was observed in the ball milled samples. Interesting magnetotransport behaviors were observed for (EuS)70Co30. Its magnetoresistance was positive at room temperature and changed to negative (-6.3%) at 100 K. Much larger negative magnetoresistance (∝-50%) was found at 20 K. These results are discussed in the context of spin fluctuation and possible spin tunneling in the system. (orig.)