Martensitic transformation and magnetocaloric effect of Ni45-xCo5Mn40+xSn10 alloys

The magnetocaloric effect (MCE) is a thermodynamic phenomenon of magnetic materials, which is subjected to the variation of magnetic field. Much effort has been put into developing the magnetocaloric materials over the past years, and a lot of materials with large magnetocaloric effect have been found, in which Ni-Mn-X (X= In, Sn, Sb, Ga) Heusler alloys attract extensive attention because it possesses structural and magnetic phase transition simultaneously, significant magnetocaloric effect and tunable phase transition temperature, etc. Due to these excellent performances, Ni-Mn based Heusler alloys have great potential applications in the field of magnetic refrigeration, magnetoelectronics, micro-actuator, and thermal magnetoelectricity conversion. Particularly, the alloy Ni₄₅Co₅Mn₄₀Sn₁₀ shows the excellent performance in magnetic properties, in which the austenite has a remarkably high magnetization, low magnetic anisotropy, and almost minimum thermal hysteresis under high applied magnetic field and furthermore at relatively small applied field. In addition, it has been proved that Mn content plays an important role in the evolution of the crystal structure of Ni-Mn based alloys, making the structure of alloys transform the cubic phase to tetragonal with increasing Mn content. Meanwhile, the alloys show a martensitic transformation when Mn content is comparatively rich, which generates a large magnetocaloric effect, making it a promising material for magnetic refrigeration technology. Therefore, in this paper, we investigate the structural and magnetic properties of Mn-rich Ni_45-xCo₅Mn_40+xSn₁₀ alloys systematically.