Martensitic and magnetic domain structures in polycrystalline shape memory alloys Ni _{2+x} Mn _{1-x} Ga

The martensitic twin and magnetic domain structures of polycrystalline samples of the shape memory Ni _{2+x} Mn _{1-x} Ga alloys are studied by magnetooptic and Bitter colloid techniques. It is shown, that the analysis of the magnetic domain structure allows one to determine the martensitic structure characteristics, such as symmetry of phases and tetragonal axes orientation. A theoretical model is in good agreement with the experiment.