One important group of shape memory alloys is the ferromagnetic Ni₂MnGa.  At room temperature, the alloy has a Heusler alloy L2₁ type structure.  A martensitic phase transition occurs upon cooling.  At the stoichiometric composition, the martensitic transformation temperature is below room temperature. Since the magnetic shape memory effect (MSM) occurs in the LT martensitic structure, non-stoichiometric alloys have been developed to enable the MSM effect at ambient conditions. One of the possibilities is the non-stoichiometric Ni₂Mn_1+xGa_1-x alloys providing modification of transformation temperature maintaining the Curie point.  The deviation from stoichiometry yields non-homogenous materials after casting due to the coring effect. Another problem is that the exchange between Mn and Ga reduces the degree of order which makes neutron diffraction more sensitive to the crystallographic characterization. In this work the crystal structure of several non-stoichiometric polycrystalline alloys were investigated at several temperatures using pulsed neutron source at Argonne National Laboratory. The following parameters were studied: The deviation from stoichiometry; temperature of isothermal heat treatment for homogenization and ordering; cooling rate after homogenization. It was found that the homogenization process at high temperature following by fast cooling is essential in order to obtain single non-stoichiometric phase. There is no indication to B2 to L1₂ transition.    

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