Tuning martensitic transformation and enhancing magnetocaloric effect in Ni$_{47}$Mn$_{40}$Sn$_{13-x}$W$_x$ Heusler alloy via experiments and first-principle insights

The influence of tungsten (W)-doping on the structural, magnetic, and magnetocaloric properties of Ni$_{47}$Mn$_{40}$Sn$_{13-x}$W$_x$ (x = 0, 0.5, 1, 1.25) metamagnetic shape memory alloys was investigated using a combination of experimental and first-principles methods. W-doping in Ni-Mn-Sn shifts the martensitic transformation (MT) towards room temperature and enhances the inverse magnetocaloric effect (MCE), with a maximum magnetic-field-induced entropy change of 13.2 J/kg·K at 5 T for the x = 1 alloy. Direct cyclic measurements at 1.96 T show stable adiabatic temperature changes (ΔT$_{ad}$ ≈ 0.5 K at the MT temperature and ΔT$_{ad}$ ≈ 1.4 K at the Curie temperature) over hundreds of cycles, confirming the cyclic stability. Density functional theory calculations reveal that the W-dopant increases the energy gap between the cubic and tetragonal crystal structures (from 15.8 to 43.6 meV), which correlates with the higher MT temperature observed in W-doped samples. The analysis of the total and local density of states identified W-induced enhancement of hybridization and a change in the density of states near the Fermi level, resulting in a shift of MT to room temperature and an improvement in MCE. ... mehrW-doping improves the MCE properties of Ni–Mn–Sn alloys, providing a path towards energy-efficient magnetic cooling.