Phase transitions in ferromagnetic Ni2+xMn1-xGa alloys with regard for themodulation order parameter

The phase diagram of ferromagnetic alloys Ni2+xMn1- xGa is reconstructed on the basis of temperature dependences of the resistance. It is seen from th is diagram that for small x, structural transitions from the cubic to the t etragonal phase are preceded by structural transformations in the cubic pha se. In the framework of the phenomenological Landau theory of phase transit ions, phase diagrams of the structural and magnetic phase transitions in th ese alloys are analyzed with regard for the modulation order parameter. It is shown that premartensitic and postmartensitic phase transitions related to the appearance of the modulated structure can occur along with martensit ic transformations. The strain and modulation order parameters substantiall y affect the magnetic phase transitions via the interaction with the magnet ic order parameter. (C) 2001 MAIK "Nauka/ Interperiodica".