A YB-170 MOSSBAUER-SPECTROSCOPY AND L(III)-EDGE STUDY OF THE KONDO-LATTICE YBCU3AL2

We present a detailed study of the magnetic and crystal-field properti es of the hexagonal Kondo lattice YbCu3Al2, using Yb-170 Mossbauer spe ctroscopy in the temperature range 0.1 K-50 K. L(III)-edge x-ray absor ption spectra at 10 K and 300 K were also obtained; they indicate that the Yb ion is very close to trivalent over the whole temperature rang e. In the antiferromagnetic phase, the thermal variation of the Yb3+ s pontaneous moment has been measured and the derived transition tempera ture (T-N = 1.95 K) is in agreement with previous specific heat and ma gnetic data. In the paramagnetic phase, the two components g(z) and g( p)erpendicular to of the g-tensor of the Yb3+ ground crystal-field dou blet have been measured. These g-values cannot be accounted for by a c rystal-field-only model, and we interpret this in terms of a Kondo red uction of the paramagnetism (T > T-N) and of the spontaneous moment (T < T-N), with a Kondo temperature T-K similar or equal to 2.3 K. In ad dition, the spectra in the antiferromagnetic phase show inhomogeneous broadenings due to the presence of random distortions with respect to the hexagonal Yb site symmetry, and, close to T-N, dynamical effects a re clearly evident and allow the Yb3+ fluctuation frequency to be meas ured in the magnetically ordered phase.