The Structural Phase Transitions in Ni ₂ MnGa induced by low-temperature uniaxial stress

An experimental study is presented of the multiple phase transitions occurring in the single crystals of Ni 2 MnGa, which had first been stressed and unloaded at liquid nitrogen temperature. The measurements of the specific heat, of the low-field magnetic susceptibility and of the ultrasonic velocity reveal that the material experiences the first-order structural phase transitions at T 3 = 190 K, at T 2 = 230 K, and at T 1 , = 290 K. The relative deformation not resulting in the plastic flow of the crystal was Δ L/L = 0.05. After unloading the dimensions and the shape of the samples were restored upon heating. The new phases appear in Ni 2 MnGa because of an anomalous instability of the lattice of this compound with respect to atomic displacements along a (110) direction in the (110) plane.