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L. Fernandez Barquin, M. de la Fuente Rodriguez, C. Echevarria Bonet, D. P. Rojas, J.C. Gómez Sal, J.I. Espeso, P. Gorria, M. Garcia-Prieto, M.L. Fdez-Gubieda, E. Bauer:
"Anomalous thermal expansion of intermediate valence YbAl3 nanometric alloys";
Poster: ICM 2015, 20th International Conference onMagnetism, Barcelona, Spain; 2015-07-05 - 2015-07-10.

The Strongly Correlated Electron System YbAl3 alloy has attracted attention due to the fact that it exhibits a variety of cutting‐edge physical phenomena [1]. Recently, we have undergone a thorough study of YbAl3 nanoparticles. X‐ray absorption measurements supported the decrease of the valence with the reduction of the size of the particles, related to the increase of the Yb2+ contribution [2]. The effect was related to the surface/volume ratio increase due to the downsizing of the particles. We have recently carried out an X‐ray diffraction (λ= 0.4126 Å, YbAl3 > 99 %) experiment at ALBA synchrotron facility. A careful crystallographic Rietveld analysis has revealed an intriguing behaviour of the thermal expansion (α) of these YbAl3 nanoparticles at 80 ≤ T ≤ 300 K. The lattice parameter variation of the D = 10 nm nanoparticles (milled during 70 h) shows an unexpected change of slope around 180 K. It should be noted that heat capacity did not exhibited any sign of transition at this temperature. It is of paramount significance that the α= 7.5 10−6 Κ−1 value inferred from the linear variation below 200 K is within the values reported for the bulk alloy, whereas the one (α= 1.5 10‐6 K-1) extracted for T > 200 K is anomalously small. The latter α value is approaching those reported for Zero Thermal Expansion (ZTE) compounds [3]. Inconsequence, the use of the size as a parameter.