The Mn-excess Ni50Mn25+xGa25-x alloys with 1 < x < 7 were developed to investigate structural transitions and magnetic properties. The martensitic transformation temperature (TM) for the structural transformation from tetragonal to cubic was clearly observed from magnetization, electrical resistivity and X-ray diffraction studies as a function of temperature for temperatures below 400 K. The TM value increased roughly from 260 K to 355 K with increasing Mn concentration and TM showed an abrupt change at the composition x = 5. For the structural transition, the Curie temperature (TC) decreased slightly from 380 K and was insensitive to variations on the Mn/Ga ratio. During the heating and the cooling processes, the samples showed a temperature hysteresis at and below TM. A magnetic-field-induced strain (MFIS) of about 0.2 % at an applied magnetic field of 4.2 kOe was derived by using the martensitic transition temperature for polycrystalline samples.
