Study of spin- and valence-fluctuation systems in the Amsterdam High-Field Installation

High-field magnetization measurements on some typical spin-fluctuation (UAl2 and UCo2) and valence-fluctuation (YbCuAl and YbCuAl-based quasiternary compounds) systems reveal common features. For both types of compounds the low-temperature magnetic isotherms exhibit abrupt changes in slope between 15 and 20 T. Further, a correlation is found between the sign of the field dependence and the sign of the temperature dependence of the initial susceptibility. For the spin-fluctuation compounds the Zeeman energy connected with the field where the kink in the low-temperature magnetic isotherms occurs is comparable with the thermal energy at Tsub(SF). Quantitatively, for UAl2 it could be established that the differential susceptibility of the high-field part of the magnetization is equal to the initial susceptibility above the spin-fluctuation temperature. For UCo2, spurious contributions to the susceptibility make quantitative conclusions impossible. (Auth.)