An alloying strategy for tuning magnetism, thermal hysteresis, and mechanical properties in Ni-Mn-Sn-based Heusler alloys

Ni-Mn-Sn metamagnetic shape memory alloys have great application potential, with numerous advantages but are constrained by limitations, such as limited magnetization differences (△M), large thermal hysteresis (△THys), and intrinsic brittleness. To ameliorate these limitations, fourth-element doping has been extensively experimentally conducted, yet theoretical insights at the atomic scale remain limited. Here, the phase stability, martensite transformation, magnetism, and mechanical properties of the Ni2Mn1.5Sn0.5 alloy doped with a 3d-transition element Z (Z = Fe, Co, and Cu) were systematically investigated using the first-principles calculations, provide theoretical explanations for changes in physical properties. The phase transformation path and magnetic properties of Ni-Mn-Sn-Z alloys containing four-layered orthorhombic (4O) martensite were revealed. The strong ferromagnetic coupling between Ni-Co and the change in MnSn magnetic moment spin direction are the primary reasons for the increase in austenite magnetic moment in Ni2-xCoxMn1.5Sn0.5 (x > 0.125) alloys. Cu doping leads to a reduction in volume contraction (△V), thereby lowering △THys. The mechanical property results indicate that Fe or Cu doping significantly enhances the plasticity and toughness, while Co doping reduces the toughness and increases stiffness. Furthermore, the origin of physical properties related to martensitic transformation and magnetism is explained by the electronic density of states. This research provides essential theoretical explanations for understanding and predicting the changes in physical properties associated with different doping elements, which is critical for the design and development of high-performance Heusler alloys.