SPIN FLUCTUATIONS IN (U1-XMX)(AL1-YCOY)2 COMPOUNDS

Experimental results involving the substitution of U atoms by M = Gd, Dy, Y, and La or Al by Co in the spin-fluctuation system UAl2 are stud ied in terms of a model calculation of the 5f-electron susceptibility. In the case of rare-earth impurities, besides the intraband f-f Coulo mb interaction, the modeL includes the Zener coupling between localize d 4f spins and itinerant 5f states. The effective f-f interaction in t he case of rare-earth impurities or the one-electron impurity-induced effects in the case of Y and La increases the proximity to a magnetic instability. Substitutional Co impurities introduce only small effects and have almost no influence on the magnetic properties of the compou nd.