Effects of Rare-Earth Doping on the Martensitic Transition Temperatures and Magnetocaloric and Transport Properties of Ni$_{50}$Mn$_{35}$Sn$_{15}$ Alloys*

The structural, magnetic, magnetocaloric, and transport properties of rare-earth (R) doped Ni$_{49}$Sm Mn$_{35}$Sn$_{15}$ and Ni$_{49}$PrMn$_{35}$Sn$_{15}$ Heusler alloys have been studied by room temperature XRD and magnetization measurements. The studied compounds show a cubic L21-type structure at room temperature. The substitution of R $=$ Sm and Pr for Ni in Ni$_{50}$Mn$_{35}$Sn$_{15}$ resulted in the shifting of the martensitic temperature (T$_{M})$ from 160 K (for Ni$_{50}$Mn$_{35}$Sn$_{15})$ to 190 K (for Sm) and 212 K (for Pr). However the Curie temperature of the austenite phase (T$_{C})$ remained unchanged (\textasciitilde 325 K). Both conventional and inverse magnetocaloric effects were observed in these compounds. The maximum value of the positive magnetic entropy change ($\Delta $S$_{M})$ near T$_{M}$ with $\Delta $H $=$ 5T was \textasciitilde 5 J/kgK and \textasciitilde 12 J/kgK for R $=$ Sm and Pr, respectively. Large values of RCP, 278 and 315 J/kg, were obtained for R $=$ Sm and Pr, respectively. The maximum values of the magnetoresistance was found to be -18{\%} (R$=$ Sm) and -30{\%} (R$=$Pr) for $\Delta $H $=$ 5T.