Normally, shape memory effect (SME) is obtained by the reverse martensitic transformation, therefore only induced by heating a sample from the deformed martensite phase. In this study, we report a phenomenon of cooling-induced SME, observed in a Co2Cr(Ga,Si) Heusler alloy, where the normal heating-induced SME can be obtained at the same time. The cooling-induced SME is attributed to an abnormal martensitic transformation in Co2Cr(Ga,Si) Heusler alloy. Moreover, an inverse temperature dependence of superelastic stress was also observed. The discoveries of these phenomena provide application possibilities for shape memory alloys, especially at low temperatures.
For the Co2Mn(Ga1−xZx) (Z=Si, Ge, and Sn) Heusler alloys, the L21/B2 order-disorder transition temperature TtL21/B2, the Curie temperature TC, and the saturation magnetization Ms were determined. The TtL21/B2 for all the systems linearly increases with increasing x. Although the TtL21/B2 was not determined in the high x region because of melting of alloys, those of Co2MnGe and Co2MnSn could be estimated by extrapolation from the quaternary data. The Ms at 4.2 K and the TC increase with x, and the Ms for all the systems is in good agreement with the Slater Pauling rule.
The concentration dependence of the order-disorder phase transformation temperature from the L21 to the B2 phase (TtL21/B2) and magnetic properties of Co2Fe(Ga1−xSix) and Co2Fe(Al1−ySiy) Heusler alloys were investigated. In the phase diagrams, a crossover of the Curie temperature (TC) and TtL21/B2 was confirmed at around y = 0.45 in Co2Fe(Al1−ySiy), whereas the TC and TtL21/B2 monotonically changed with x in Co2Fe (Ga1−xSix). The slopes of the linear concentration dependence of TtL21/B2 for Co2Fe(Al1−ySiy) drastically changed at about y = 0.45, suggesting that the chemical interchange energy between Fe and Al in Co2FeAl alloy is affected by the magnetic ordering.
Magnetic properties of the B2 phase in Co50−xNixMn25Al25 alloys were investigated. Spontaneous magnetization Ms measured at 4.2 K increases linearly with increasing x in the region of x ≤ 30 in accordance with following the generalized Slater-Pauling (GSP) line. However, Ms abruptly decreases with increasing x and deviates from the GSP line in the Ni-rich region of x > 30, suggesting a drastic change in the density of states at the Fermi energy. The Curie temperature TC decreases monotonically with increasing x and significantly decreases in the region of x > 30. Antiferromagnetic evidence is clearly observed at x > 45, and the Néel temperature TN increases with increasing x, in reaching the value of the B2 phase in Ni2MnAl.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.