Ultrasonic study of the phase transition in Ni2MnGa

The ultrasonic attenuation and velocity of waves associated with the three independent elastic constants C₁, C₄₄ and C´ were studied as a function of temperature in a Ni₂MnGa single crystal. Recent neutron diffraction studies have reported the existence of an intermediate phase transition near 265K in this alloy. The present ultrasonic measurements confirm the existence of this intermediate phase transition. All three elastic constants soften as the temperature is lowered from 300K to 265K. Also, large increases in attenuation are observed as the temperature is lowered. Pretransformation effects are observed for temperatures as high as 285K for the C´ elastic constant. The velocities obtained from the neutron data are consistent with the velocities directly measured by the ultrasonic technique. The ultrasonic measurements will be compared with the neutron scattering results in Ni₂MnGa and also with the elastic behavior near the martensitic phase transformation in NiAl alloys