Martensitic Transformation and Magnetocaloric Effect of Ni45−xCo5Mn40+xSn10 Alloys

The structural, magnetic, and martensitic transition properties of Ni_45-xCo₅Mn_40+xSn₁₀ ($x=2$ , 4, 6, and 8) alloys are investigated systematically. X-ray diffraction reveals that the alloys mainly exhibit a tetragonal phase at room temperature, but also a small amount of impurity phase when the Mn content is >46%. The temperature dependence of magnetization indicates that there are two different magnetic transitions in the alloys, the Curie transition and the martensitic transition. With the substitution of Mn for Ni, the Curie temperature of alloys remains almost unchanged, while the martensitic transition temperature decreases, which is attributed to the decrease in the valence electrons concentration. In particular, the strong coupling between magnetism and structure occurs in Ni_45-xCo₅Mn_40+xSn₁₀ alloys, and the Ni₄₃Co₅Mn₄₂Sn₁₀ alloy exhibits a large magnetic entropy change of 30.6 Jkg^-1K^-1 at a field change of 3 T in martensitic transition, making it a good candidate for magnetic refrigeration materials.