The effect of alloying element aluminum on the magnetic properties and martensitic transition in Ni8Mn6Sn2−xAlx shape memory alloys has been studied using the density-functional theory. It is found that the tetragonality, c/a, of the martensite phase increases gradually from 1.30 to 1.34 with increasing Al content. The equilibrium equation of state results show that the alloys Ni8Mn6Sn2−xAlx exhibit an antiferromagnetic-ferromagnetic phase transition in the austenite phase with x increasing. In particular, when x = 2, an unique magnetic transition occurs from ferromagnetic austenite (6.30 μB/f.u) to antiferromagnetic martensite (1.82 μB/f.u), as characterized by the spin polarized electronic density of states.

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