Effect of the selected alloying on Ni-Mn-Ga alloys

The aim of the present study was to investigate the possibilities of changing some characteristics of ternary Ni-Mn-Ga alloys by alloying. Therefore, five quaternary materials were prepared from the same polycrystalline Ni-Mn-Ga master ternary alloy with about 2 at.% additions of Bi, Pb, Si, Sn and Zn. The transformation temperatures and Curie points of the annealed materials were determined with DSC and magnetic susceptibility measurements. The crystal structures of the alloys were determined with the X-ray diffraction. In alloys with Si and Sn phase transformations were retarded to very low temperatures or outside the observable temperature region (below 113 K). With Si alloying a clear premartensitic softening was present. Bi, Pb and Zn doping preserved the original monoclinic crystal structure of the master alloy with slight lattice parameter changes. Bi increased slightly the phase transformation temperatures and decreased the Curie point, while in the two others phase transformations were shifted little lower and Curie temperature to higher temperatures. The intermartensitic transformation present in the ternary alloy was either totally retarded or diminished to a large extent in all of the doped alloys