MAGNETIC AND NMR-STUDY OF VALENCE PHASE-TRANSITION IN YBIN1-XTXCU4(T = AG AND AU)

The magnetic susceptibility, In-115 Knight shift and Cu-63 NQR frequency nu(Q) in YbIn1-xTxCu4 (T = Ag and Au) with x less-than-or-equal-to 0.1 have been measured in order to investigate the valence phase transition at T(v) = 40 K. For x = 0 they exhibit drastic changes at T(v). The Ag or Au substitution increases T(v) and also decreases nu(Q), which is mainly ascribed to an increase in its electronic contribution and suggests a change in the 4f and conduction electron hybridization. The effect of the Ag substitution on T(v) and nu(Q) is more remarkable, probably because of a heavy fermion character of YbAgCu4.