Structural and magnetic phase transitions in shape-memory alloys Ni2+xMn1-xGa

The Heusler-type alloy Ni2+xMn1-xGa exhibits well defined shape memory prop erties in a ferromagnetic state, which means that the martensitic transitio n temperature is lower than the Curie point of this material. The change of composition makes these characteristic temperatures approach each other. T o study this behavior, the measurements of specific heat, ac magnetic susce ptibility, and de resistivity were performed. The phase diagram of the cubi c ferromagnet describing possible structural and magnetic transitions is ob tained theoretically. This diagram is compared with experimental data on Ni 2+xMn1-xGa. An estimate is given of the magnetic-field influence on the tem perature of martensitic transformation in the studied alloys. [S0163-1829(9 9)09701-5].