Anomalous physical properties of Heusler-type Co2 Cr (Ga,Si) alloys and thermodynamic study on reentrant martensitic transformation

Electronic, magnetic, and thermodynamic properties of Co2Cr(Ga,Si)-based shape-memory alloys, which exhibit reentrant martensitic transformation (RMT) behavior, were studied experimentally. For electric resistivity (ER), an inverse (semiconductor-like) temperature dependence in the parent phase was found, along with anomalous behavior below its Curie temperature. A pseudobinary phase diagram was determined, which gives a "martensite loop" clearly showing the reentrant behavior. Differential scanning calorimetry and specific-heat measurements were used to derive the entropy change ΔS between martensite and parent phases. The temperature dependence of the derived ΔS was analyzed thermodynamically to confirm the appearances of both the RMT and normal martensitic transformation. Detailed studies on the specific heat in martensite and parent phases at low temperatures were also conducted.