Enhanced Cryogenic Magnetocaloric Effect Induced by Small Size GdNi 5 Nanoparticles

GdNi5 nanoparticles and GdNi5/Gd2O3nanocapsules（with GdNi5 core and Gd2O3 shell） were prepared by arcdischarge technique under different hydrogen partial pressure.The GdNi5 nanoparticles show irregular spherical shape and have a size distribution of 10—50 nm with an average diameter of 15 nm.In comparison,the GdNi5/Gd2O3 nanocapsules present spherical morphology and show a size distribution of 10—100 nm with an average diameter of 60 nm.Under a magnetic field change of 50 kOe,the maximum magnetic entropy change of GdNi5 nanoparticles is 13.5 J/（kg K） at 5 K,while the corresponding value of the GdNi5/Gd2O3nanocapsuels is only 5.7 J/（kg K） at 31 K.The origin of the large magnetic entropy change of GdNi5nanoparticles is ascribed to its high atomic moments and small anisotropy energy barrier induced by its small particle size.