Synthesis of a new type of GdAl2nanocapsule with a large cryogenic magnetocaloric effect and novel coral-like aggregates self-assembled by nanocapsules

A new type of GdAl2 nanocapsule with single-phase intermetallic compound GdAl2 as the core and amorphous Al2O3 as the shell has been synthesized by the arc-discharge technique with modified strategies. Meanwhile, novel three-dimensional coral-like hierarchical branching macro-aggregates were self-assembled by disordered nanocapsules synthesized simultaneously in the arc-discharge process. The GdAl2 nanocapsules display superparamagnetic properties between their blocking temperature of 100 K and Curie temperature of 162 K. The magnetocaloric effect of the GdAl2 nanocapsules was measured between 5 and 165 K. The absolute value of the change of magnetic entropy of the GdAl2 nanocapsules sharply increases with decreasing temperature and reaches 14. 5Jk g −1 K −1 at 5 K in magnetic fields varying from 0 to 50 kOe. As a result, this new type of nanocapsule can prospectively be applied in cryogenic magnetic refrigerator devices.