Stress and temperature dependence of the structure of the martensite and X-phase in Ni2MnGa

Stress and temperature dependence of the structure of the X-phase in Ni2MnGa has been investigated by neutron diffraction measurements to clarify the structural relationship among the parent (P-), intermediate (I-), martensite (M-) and X-phases. The satellite position and intensity of the X-phase differ from those of the I-phase under compressive stress, but approach those of the I-phase with increasing temperature and decreasing stress. In other words, the structure changes discontinuously with I X transformation under compressive stress, but continuously under zero stress. On the other hand, the X P transformation is continuous, regardless of stress or temperature. These results suggest the existence of a multicritical point for successive P X I transformation.