YB-170 MOSSBAUER STUDY OF THE CRYSTALLINE ELECTRIC-FIELD AND EXCHANGE INTERACTION IN YBFE2

The Moessbauer study of **1**7**0Yb in YbFe//2 was performed in the temperature range 4. 2-60K. The thermal variations of the hyperfine field and of the electric quadrupole coupling suggest that the crystalline field effects on the ytterbium ion are rather small and we get good least square fits with pure exchange only ( mu //B H//e//x/k//B equals 111 plus or minus 4 K); the corresponding values of the conduction electron field and of the Sternheimer shielding factor are respectively H//c equals 240 plus or minus 100kOe and R//Q equals 0. 22 plus or minus 0. 01. In connection with the smallness of the crystalline field, we discuss the influence of the magnetostriction on the crystalline potential seen by a rare earth ion in the RFe//2 compounds.