Specific-heat study of nanocrystalline palladium

Abstract

We have performed measurements of the low-temperature specific heat for T=0.7--20 K and magnetic susceptibility for T=1.8--300 K of Pd nanocrystals with average particle size 84 \AA{}. An enhancement of the specific heat is observed at temperatures T>3.5 K for 84-\AA{} Pd nanocrystals. This enhancement is primarily related to the softening of and the size effect on the phonons. The temperature coefficient of specific heat \ensuremath{\gamma} decreases to a lower value as compared to that of bulk Pd. An estimated surface coefficient of specific heat ${\ensuremath{\gamma}}_{\mathit{s}}$ is about 30% that of the bulk. This is also reflected in a reduction of the magnetic susceptibility of the Pd nanocrystals. The peak of the magnetic susceptibility observed at \ensuremath{\sim}80 K in bulk Pd is not observed in the nanocrystals; this could be due to a change of the energy band structure in the Pd nanocrystals.