The phase diagram of Ni–Mn–Ga alloys with account of crystal lattice modulation and external magnetic field

The phase diagram of Ni–Mn–Ga Heusler alloys is investigated theoretically with the help of Ginzburg–Landau theory including magnetic, elastic and crystal lattice modulation order parameters as well as an external magnetic field. The influence of the parameters of the Ginzburg–Landau functional on the phase diagrams is discussed in detail. It is shown that the volume and anisotropic magnetostriction have significant influence on the phase diagrams of Ni–Mn–Ga alloys. For an appropriated combination of phenomenological parameters, the sequence of the phase transitions is in good agreement with the experimental ones. The condiditons for the existence of a critical point in the H–T diagram are discussed.