Entropy change at the martensitic transformation in ferromagnetic shape memory alloys Ni_{2+x}Mn_{1-x}Ga

The entropy change $\mathrm{\Delta }S$ between the high-temperature cubic phase and the low-temperature tetragonally-based martensitic phase of Ni${}_{2+x}$Mn${}_{1-x}$Ga ($x=0-0.20$) alloys was studied. The experimental results obtained indicate that $\mathrm{\Delta }S$ in the Ni${}_{2+x}$Mn${}_{1-x}$Ga alloys increases with the Ni excess $x$. The increase of $\mathrm{\Delta }S$ is presumably accounted for by an increase of magnetic contribution to the entropy change. It is suggested that the change in modulation of the martensitic phase of Ni${}_{2+x}$Mn${}_{1-x}$Ga results in discontinuity of the composition dependence of $\mathrm{\Delta }S$.