Cryogenic magnetocaloric effect in Gd2O3 nanoparticles studied by heat capacity

Structural characteristics and magnetic properties with respect to magnetocaloric effect was studied in the nanocomposite systems consisting of Gd2O3 nanoparticles embedded in the regular pores of amorphous silica matrix. The particles of size 2-16 nm were prepared by nanocasting method within the pores of periodic silica matrices of hexagonal (SBA15 type) and cubic (SBA16 type) symmetries. Magnetocaloric response of the systems was examined in the applied fields up to 9 T in the low temperature region ranging from 0.4 K to 55 K. The data obtained from the measurements of the heat capacity C-p(H,T) revealed a peak at temperature below 10 K. Taking into account the superposition principle, the contributions corresponding to the lattice and the magnetic subsystem heat capacities were analyzed separately. The high value of magnetic entropy change vertical bar Delta S-M vertical bar = similar to 27 JK(-1)kg(-1) and vertical bar Delta S-M vertical bar = 37 JK(-1)kg(-1) for the systems with hexagonal and cubic matrices, respectively were observed at the temperature close to 2 K under field change from 0 to 9 T. The evidence on considerable high vertical bar Delta S-M vertical bar values along with the large surface area of mesoporous silica, easy and reproducible preparation manifest some extra advantages over the conventional refrigeration technology.