Phase diagram and magnetic moment of Ni50+Mn27−Ga23 ferromagnetic shape memory alloys

Abstract

Abstract Permeability, magnetization, differential scanning calorimetry and X-ray powder diffraction measurements were carried out on the off-stoichiometric ferromagnetic shape memory alloys Ni 50+ x Mn 27− x Ga 23 (−25 ⩽ x ⩽ 6) in order to establish the phase diagram over a wide range of concentration. The phase diagram was found to comprise of four regions, a paramagnetic austenite phase (Para-A), a paramagnetic martensite phase (Para-M), a ferromagnetic austenite phase (Ferro-A) and a ferromagnetic martensite phase (Ferro-M). Furthermore the martensitic transformation and the Curie temperatures crossed over at around x = 2.5. The martensitic transformation was found to occur over a wide Mn-rich region. A linear increase in the martensitic transformation temperature with increasing number of valence electrons per atom, e / a , was limited to a narrow concentration range around x = 0.0. Overall the martensitic transformation temperature exhibited a concave behavior with a minimum occurring at approximately x = −8.