Abstract
The thermal transformation and magnetic properties of Ni49.0Mn27.2Ga23.8 single crystals were investigated. A martensitic transformation was observed at 172 K during cooling. At this temperature, the strain in the [100] direction under an applied field of 10.1 kOe in a direction parallel to the [100] plane was approximately −8000 ppm. The entropy change in this transformation was estimated as 5.6 J/kg·K by calorimetric measurement. On the other hand, an intermediate phase transformation was observed at 230±2 K. The entropy change was 0.3 J/kg·K. At this temperature, the thermal expansion coefficient was increased, the magnetization in the low-field region was decreased, and the magnetostriction in the [100] direction was increased. The magnetostriction at 232 K was 2.3 times larger in the parallel field and 7.3 times larger at 228 K in the vertical field than the values at room temperature.
