Crystal structure and transformation behavior of Ni–Mn–Ga martensites

The crystal structure of the martensitic phase Ni–Mn–Ga ferromagnetic shape memory alloys has been found to be extremely sensitive to composition. A systematic exploration of the composition–structure relationship has been performed using X-ray diffraction on several single crystals having large composition gradients. Also, temperature-dependent magnetic measurements show the martensitic transition to orthorhombic martensite is broader than to tetragonal martensite. This distinct character can be understood by considering the relative importance of strain energy effects in the two martensite phases.