Results of temperature-dependent magnetic susceptibility and powder x-ray diffraction (XRD) measurements on ${\mathrm{Ni}}_2{\mathrm{Mn}}_{1.05}{\mathrm{Ga}}_{0.95}$ and ${\mathrm{Ni}}_{2.13}{\mathrm{Mn}}_{0.87}\mathrm{Ga}$ magnetic shape memory alloys are compared. The transformation behavior of these two alloys is found to be entirely different. Detailed LeBail and Rietveld analyses of powder XRD data of ${\mathrm{Ni}}_2{\mathrm{Mn}}_{1.05}{\mathrm{Ga}}_{0.95}$ alloy show that the martensite phase belongs to the Pnnm space group with $7M$ modulation. The limits of the supercooled austenite and the superheated martensite phases have been determined by Rietveld analysis of powder XRD data recorded at close temperature intervals. It is shown that the martensite and the austenite phases coexist over $\sim 30\mathrm{K}$ temperature range around the martensitic transition temperature. The transformation strains during cooling in [001], [010], and [100] directions are found to be $-4\%$, $+1.6\%$, and $2.1\%$, respectively, while the volume change is only 0.06%.

• Received 24 January 2006

DOI:https://doi.org/10.1103/PhysRevB.74.224443