Ferromagnetism and spin-glass transitions in the Heusler compoundsRu2−xFexCrSi

Abstract

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.

Spin polarization of Fe-rich ferromagnetic compounds in Ru2−Fe CrSi Heusler alloys

“…For fully ordered Ru 2 À x Fe x CrSi, the predicted saturation magnetic moment should be 2 m B per formula unit [16]. The XRD measurements for these samples, which are presented elsewhere [17], indicate that Ru 2 À x Fe x CrSi is completely L2 1 structure.…”

“…We were successful to synthesize Ru 2 À x Fe x CrSi polycrystals and the physical properties of Ru 2 À x Fe x CrSi were clarified so far [17]. In this paper, we focus on spin polarization P of Ru 2 À x Fe x CrSi measured by the Andreev reflection technique using Ru-based Heusler alloy/superconductor junctions.…”

Low-temperature magnetic properties of Heusler compoundsRu2−xFexCrSi<

“…angular momentum S = 1 was predicted for these concentrations. 8 This S value leads to S m = R ln͑3͒ = 9.13 J / K mol. Here, R is the gas constant.…”

“…Unfortunately, in this system, it is unclear which atom is responsible for the magnetic moment at this stage. 7,8 Figures 3͑a͒-3͑c͒ are plots of specific heat C P ͑T͒ versus T in the temperature range between 1.4 and 80 K for x = 0.1, 0.3, and 0.5, respectively. No discontinuity indicating longrange order is observed for any of the samples around the temperature at which M͑T͒ / H has peak-type ͑at T f1 ͒ and irreversibility-type ͑at T f2 ͒ anomalies.…”

“…[3][4][5] In a theoretical study, it was pointed out that Ru 2−x Fe x CrSi is a strong candidate material in which the half metallicity is preserved in the presence of higher level defects and randomness of the crystalline structure. 6 Hiroi et al [7][8][9] synthesized Ru 2−x Fe x CrSi compounds over a wide range of x, and investigated their transport and magnetic properties. For 1.4Յ x Ͻ 2.0, Ru 2−x Fe x CrSi shows ferromagnetic transition at a Curie temperature T C ϳ 500 K. With x decreasing from x ϳ 1.4, T C decreases linearly, and the system becomes antiferromagnetic below x = 0.2.…”