Reduction of the Yb valence in YbAl3 nanoparticles
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AuthorRojas Pupo, Daniel; Fernández Barquín, Luis; Espeso Martínez, José Ignacio; Rodríguez Fernández, Jesús; Chaboy, J.
Measurements of specific heat, dc magnetic susceptibility, and Yb LII and LIII x-ray absorption near-edge
structure XANES and extended x-ray absorption fine structure EXAFS on YbAl3 milled alloys are reported.
X-ray diffraction patterns are consistent with a reduction in particle size down to 10 nm and an increase in the
lattice strain up to 0.4% for 120 h of milling time. A decrease in the mean valence from 2.86 for the unmilled
alloy to 2.70 for 120 h milled YbAl3 is obtained from the analysis of XANES spectra. From the analysis of
spectra in the EXAFS region, an increase in the mean-square disorder of neighbor distance with milling time
is detected in good agreement with the results of x-ray diffraction. Size effects strongly influence the magnetic
and thermal properties. The value for the maximum of the magnetic susceptibility decreases around 30% for
120 h milled alloy and an excess specific heat, with a peak around 40 K in the milled samples, is derived.
These changes in the physical properties along the milled YbAl3 alloys are associated with the reduction in
particle size. Such a reduction leads to the existence of a large number of Yb2+ atoms at the surface with
respect to the bulk affecting the overall electronic state.
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