Magnetocaloric effect in bulk nanocrystalline Gd metals by spark plasma sintering

摘要

Bulk nanocrystalline gadolinium metals have been consolidated from gadoliniumnanoparticles using spark plasma sintering. Transmission electron microscopyobservation shows that SPS technique can effectively restrain the grain growth inbulk Gd metals. The adiabatic temperature changes of the as-consolidated andcoarse-grained gadolinium metals were measured directly using a homemademagnetocaloric effect (MCE) measuring apparatus with a magnetic-field changeof 1.5 T. With the decrease of Gd grains from micrometre to nanometre range, theadiabatic temperature change drops surprisingly from 3.5 to 1.1 K, and theirresultant adiabatic temperature change uniformly peaks at 298, 296 and 288 K,respectively, corresponding to the magnetic transition temperature of the threesamples. The Curie temperature TC of the nanocrystalline Gd shifts by more than10 K below that of coarse-grained Gd sample. However, the value of adiabatictemperature change of the as-consolidated sample at low temperature exhibitsa more constant tendency compared with the coarse-grained sample. On the otherhand, nanostructures do not change the magnetic transition and still preserve thesecond-order magnetic transition in the bulk nanocrystalline Gd metals.All results indicate the remarkable influence of the nanostructure on the MCEsof Gd due to the finite size effect.