Thermal properties and microstructure of bulk nanocrystalline Gd material

Bulk nanocrystalline gadolinium (Gd) material has been consolidated from Gd nanoparticles using spark plasma sintering (SPS). High density (>99.5%) bulk nanocrystalline material was achieved after sintering at a temperature of 280 °C with a pressure of 500 MPa. Microstructure analysis shows that the consolidated bulk material exhibits a single phase with hexagonal close packed structure and a fine grain microstructure with a mean grain size of about 15 nm. The structural transformation from hexagonal condensed packed to face centered cubic was not observed, and the second-order magnetic transition remained in the nanocrystalline Gd sample. The Curie temperature of the nanocrystalline Gd decreased by more than 10.7 K below that of the coarse-grained. The activation energies for the coarse-grained and the as-consolidated Gd materials are 2.7702 and 1.0130 eV, respectively.