Lotus leaf-inspired superhydrophobic strategy to prepare high-quality Ni50Mn35In15 single-crystal spheres for magnetic refrigeration

The Ni-Mn based ferromagnetic shape memory alloys (FSMAs) usually show large magnetocaloric effects for the first order magnetic phase transition. In the view of the practical applications, the high sphericity and surface smoothness of the magnetic refrigerant particles are essential to improve heat exchange efficiency and avoid pressure drop in the active magnetic regenerator cycle. However, it is difficult to synthesis FSMAs spheres due to their poor mechanical performance. Inspired by lotus leaf, high-quality Ni50Mn35In15 single-crystal spheres are successfully prepared through a superhydrophobic strategy. The designed spheres exhibit perfectly spherical shape, smooth surface and are fully dense without pores or inclusions. Benefit from the static heat treatment process, the spheres present single-crystal structure and enhanced mechanical homogeneity. As for the magnetocaloric performance, the spheres show a large magnetic entropy change of 11.8 J kg-1 K-1 and a high effective refrigeration capacity of 102.6 J kg-1 with a magnetic field change of 5 T around room temperature, which are larger than these of the Ni50Mn35In15 raw material. This work provides a promising approach to prepare highquality single-crystal FSMAs spheres for the magnetic refrigeration.