Magnetic phase diagram of Ni2Mn1.44−xCuxSn0.56 shape memory alloys

• The magnetic phase diagram of Cu-modified Ni–Mn–Sn shape memory alloys was first established.
• Substitution of Cu for Mn slightly increases magnetization whereas the Cu element has no magnetic moment.
• TC was decreased by pressure, suggesting the important role of the nearest neighbor exchange interaction of Mn–Mn.

Magnetization measurements have been carried out on the magnetic shape memory alloys (MSMAs) Ni2Mn1.44−xCuxSn0.56 (0 ⩽ x ⩽ 0.09). On the basis of the experimental results, the phase diagram of Ni2Mn1.44−xCuxSn0.56 (0 ⩽ x ⩽ 0.09) alloys in the temperature-concentration plane has been determined. The resultant phase diagram is spanned by paramagnetic austenite (Para-A), ferromagnetic austenite (Ferro-A) and ferromagnetic martensite (Ferro-M) phases. The martensitic transition temperature TM makes a broad maximum as a function of x, whereas, in the austenite phase the Curie temperature TC decreases slightly with x. The TC of Ni2Mn1.415Cu0.025Sn0.56 was found to decrease linearly with pressure, whereas TM increased linearly with pressure. The values of dTM/dp and dTC/dp of Ni2Mn1.415Cu0.025Sn0.56 were found to be 0.88 K/kbar and −0.31 K/kbar, respectively.