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The results of a comprehensive study of the structural, magnetic, and magnetotransport properties of the Heusler compounds Ru 2−x Fe x CrSi are presented. The Fe-rich compounds ͑x Ն 1.5͒ exhibit a usual ferromagnetic transition. The Ru-rich compound ͑x = 0.1͒ does not show ferromagnetism but exhibits a peak in magnetic susceptibility at T N ‫ء‬ = 30 K. Nevertheless, specific-heat measurements show that there is no antiferromagnetic transition at T N ‫ء‬ nor at any other temperatures. With further decreasing temperature strong irreversible behavior occurs below a temperature T g . It is proposed that these results can be interpreted as successive spin-glass transitions at T N ‫ء‬ and T g . The compounds with intermediate x ͑=0.3 and 0.5͒ are found to be ferromagnetic.Both the saturation magnetization and the Curie temperature T C 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.

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We carried out magnetization M͑T͒ and specific-heat C P ͑T͒ measurements of the new Heusler compounds Ru 2−x Fe x CrSi ͑x = 0.1, 0.3, and 0.5͒, which exhibit spin-glass freezing. M͑T͒ has peak-and irreversibilitytype anomalies. The temperatures at which these anomalies appear have magnetic field dependence described by the Gabay-Toulouse and de Almeida-Thouless lines in the low-field range. For the magnetic specific heat C m ͑T͒, we did not observe a discontinuity indicating long-range magnetic phase transition but a broad hump characteristic of spin-glass freezing. C m ͑T͒ in the low-temperature range is described as a combination of linear-and quadratic-T terms. The quadratic-T dependence of C m ͑T͒ is probably associated with excitation of the Ising component of the freezing spins.

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