New aspects of structural and magnetic behaviour of martensites in Ni-Mn-Ga alloys

The structural changes and magnetic anomalies accompanying martensitic transformations tit Ni-Mn-Ga allows are briefly, discussed. The role of lattice tetragonality of martensite in the reduction of magnetic field needed for the observation of large magnetostrain effect is theoretically analyzed, considering the compensation of the magnetic anisotropy. The possibility of the field reduction is based on the previously observed lattice parameter dependence on the temperature and proper tit of the alloy specimen shape. The model shows that a significant reduction of the magnetic field needed for the giant MSE can take place in martensites with 0.98 < c/a < 1.04.