Martensitic transformation in Ni-Mn-Ga alloy under high magnetic fields

An effect of magnetic field on the martensitic transformation (MT) temperature in ferromagnetic shape memory Ni49.4Mn27.7Ga22.9 single crystal with the MT temperature 285 K is studied by measuring and theoretical treatment of the magnetization versus temperature dependencies in a wide range of the high magnetic fields higher than saturating one. In this way, a linear approximation of the field dependence of MT temperature was proved for the high-field range. The linear increase of transformation temperature is characterized by the slope of 3.5×10-2 K/kOe. This value is essentially larger than the value 2×10-2 K/kOe reported by Gonzales-Comas et al. [Phys. Rev. B 60 (1999) 7085-7090] for the Ni49.5Mn25.4Ga25.1 alloy with a low MT temperature. This difference is in an agreement with the predictions of the Landau theory.