The effect of Co-doping on martensitic transformation temperatures in Ni–Mn–Ga Heusleralloys

Abstract

The effect of Co-doping in non-stoichiometric Ni–Mn–Ga alloys on martensitictransformation temperatures is investigated. Experimental results showthat the effect of Co addition on martensitic transformation temperaturesis remarkable, but the Heusler structure of the alloys remains unchanged. ForNi48Mn27Ga25−xCox (x = 1,2, 3, 4) alloys, the martensitic transformation temperatures increase monotonically withincreasing Co substitution for Ga. The effect can be attributed to the variation ofintrinsic factors, i.e. the decrease in the unit-cell volumes and the increase in theelectronic concentrations and density. The martensitic transformation temperatures ofNi48Mn26−xCoxGa26 (x = 1,2, 3, 5) alloys do not change much with the variation of Co substitution and intrinsicfactors have no effect on the exceptional behaviour, which implies that many factors shouldbe considered simultaneously when designing practical alloys.