Ferromagnetism and spin-glass transitions in the Heusler compounds Ru2-x Fex CrSi

The results of a comprehensive study of the structural, magnetic, and magnetotransport properties of the Heusler compounds Ru2-x Fex CrSi are presented. The Fe-rich compounds (x 1.5) exhibit a usual ferromagnetic transition. The Ru-rich compound (x=0.1) does not show ferromagnetism but exhibits a peak in magnetic susceptibility at TN =30K. Nevertheless, specific-heat measurements show that there is no antiferromagnetic transition at TN nor at any other temperatures. With further decreasing temperature strong irreversible behavior occurs below a temperature Tg. It is proposed that these results can be interpreted as successive spin-glass transitions at TN and Tg. The compounds with intermediate x (=0.3 and 0.5) are found to be ferromagnetic. Both the saturation magnetization and the Curie temperature TC increase with increasing x. However, being different from the Fe-rich compounds, hysteresis of the magnetization is observed and this suggests that the ferromagnetism has glassy character. In lower-temperature range fairly large negative magnetoresistance are observed. These results are suggestive of a magnetically inhomogeneous ferromagnetic state, that is, the formation of ferromagnetic clusters.