Effect of uniaxial compressive stress on martensitic transformation has been investigated in a single crystalline Ni₂MnGa, which exhibits a parent to an intermediate (P→I) phase transformation at T_I (250K) and successively an intermediate to 10M (I→10M) phase transformation at T_M (200 K). We found that a new phase, which is referred to as X-phase, appears under a compressive stress applied along [001]_P direction. That is, in a stress applying process, a successive I→X→10M or P→X transformation appears depending on temperature. On the other hand, in a cooling process under a stress applied along [001]_P direction, a successive P→X→I→10M or P→X→10M transformation appears depending on the strength of the stress. The I→X and the X→10M transformations are both first order with an apparent temperature hysteresis, but no hysteresis is observed for the P→X transformation. The X→10M and the P→X transformation temperatures increase as stress increases, but the I→X one decreases as stress increases. The increasing ratios against compressive stress, dT/dσ, are about 0.5 K/MPa, 0.3 K/MPa and −4.0 K/MPa for the X→10M, the P→X and the I→X transformations, respectively.

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1. Crystal structure of martensite and intermediate phases in Ni₂MnGa studied by neutron diffraction