Relation between martensitic transformation temperature range and lattice distortion ratio of NiMnGaCoCu Heusler alloys

In order to study the relation between martensitic transformation temperature range D T (where D T is the difference between martensitic transformation start and finish temperature) and lattice distortion ratio (c/a) of martensitic transformation, a series of Ni46Mn28-xGa22Co4Cux (x = 2-5) Heusler alloys is prepared by arc melting method. The vibration sample magnetometer (VSM) experiment results show that Delta T increases when x > 4 and decreases when x < 4 with x increasing, and the minimal Delta T (about 1 K) is found at x = 4. Ambient X-ray diffraction (XRD) results show that Delta T is proportional to c/a for non-modulated Ni46Mn28-xGa22Co4Cux (x = 2-5) martensites. The relation between Delta T and c/a is in agreement with the analysis result obtained from crystal lattice mismatch model. About 1000-ppm strain is found for the sample at x = 4 when heating temperature increases from 323 K to 324 K. These properties, which allow a modulation of D T and temperature-induced strain during martensitic transformation, suggest Ni46Mn24Ga22Co4Cu4 can be a promising actuator and sensor.