Valence state of CeAl2 nanoparticles studied by Ce L3-edge x-ray absorption spectroscopy

We report measurements of the Ce L3-edge x-ray absorption near-edge structure on CeAl2 nanoparticles with average diameters of 80 A. The Ce exhibits a mixed valence with a small amount of tetravalent Ce, which is in contrast to the purely trivalent Ce observed in bulk CeAl2. A shift in the absorption edge to higher energy and a narrower linewidth are also observed in the nanoparticle samples. These spectral differences are attributed to surface effects caused by the small particle size, including a lower coordination number and higher surface pressure. The observation of nonmagnetic tetravalent Ce with the 4f0 configuration is in good agreement with the small values of magnetic entropy seen in low temperature specific heat measurements.