Tuning the magnetocaloric properties of the $Ni2+xMn1−xSn$ Heusler alloys

We report the effect of Ni substitution on the magnetic properties of polycrystalline $Ni2+xMn1−xSn$ (x = 0, 0.05, and 0.1) Heusler alloys using the magnetization and neutron diffraction measurement techniques. The paramagnetic to ferromagnetic transition temperature (Curie temperature, $TC$⁠) has been tuned with the substitution of Ni at the Mn sites (⁠$TC≈$ 349, 337, and 317 K for x = 0, 0.05, and 0.1 samples, respectively) without a significant reduction in the magnetic entropy change $−ΔSM$⁠. For a magnetic field change from 0 to 5 T, $−ΔSM$ of 2.9, 2.5, and $2.2 J kg−1 K−1$ have been observed for x = 0, 0.05, and 0.1 samples, respectively. From the neutron diffraction study, it has been found that with increasing x, the Mn site ordered moment decreases. $−ΔSM$ as a function of changing magnetic field and Curie temperature follows the molecular mean field model. The studied $Ni2+xMn1−xSn$ alloys, with their nontoxic constituent elements and low-cost, can be used for magnetic cooling over a wide temperature range of 278–379 K covering room temperature.