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 ΔT (where ΔT is the difference between martensitic transformation start and finish temperature) and lattice distortion ratio (c/a) of martensitic transformation, a series of Ni₄₆Mn_28-xGa₂₂Co₄Cu_x (x= 2-5) Heusler alloys is prepared by arc melting method. The vibration sample magnetometer (VSM) experiment results show that ΔT increases when x> 4 and decreases when x< 4 with x increasing, and the minimal ΔT (about 1 K) is found at x=4. Ambient X-ray diffraction (XRD) results show that ΔT is proportional to c/a for non-modulated Ni₄₆Mn_28-xGa₂₂Co₄Cu_x (x= 2-5) martensites. The relation between ΔT 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 ΔT and temperature-induced strain during martensitic transformation, suggest Ni₄₆Mn₂₄Ga₂₂Co₄Cu₄ can be a promising actuator and sensor.