Effect of the chemical composition to martensitic transformation in Ni–Mn–Ga–Fe alloys

Recently, there have been studies of the influence of Fe addition in Ni–Mn–Ga alloys. In the present study, the aim was to investigate the effect of iron alloying in Ni–Mn–Ga compound on transformation temperatures, crystal structures and magnetic shape memory (MSM) properties. Alloying was carried out by applying two main ideas: (1) by using different Fe-contents from 0.7 to 11.4 at.% and (2) by variation of the Ni–Mn–Ga composition ratios with fixed 2 at.% Fe. The alloys were manufactured with induction melting in Ar-atmosphere with alumina Bridgman crucibles. The transformation temperatures together with Curie point were determined by DSC and magnetic susceptibility measurements. Chemical compositions were obtained with SEM-EDS studies. It is shown that clear increase of the iron content raises the Curie point and lowers the martensitic transformation temperatures. Also, addition of Fe in some cases changes the structure that was confirmed by applying X-ray crystal structure study. The ratio between Ni, Mn and Ga was confirmed to affect strongly on the crystal structure of the obtained martensite in the quaternary Ni–Mn–Ga–Fe alloy. Furthermore, the twinning stresses and MSM properties of one of the alloys are presented.