Influence of 5d-metal on magnetic properties of UNi1-xTxAl compounds

We have studied structure and magnetic properties of UNi1-xTxAl (T=Ir, Pt) alloys. UNiAl does not form continuous solid solutions with either UPtAl or UIrAl. The solubility ranges extend only to 20% from each side in both sys tems. The alloys with 0.20<x<0.80 contain two isostructural phases with the ZrNiAl-type structure. Ln both systems, the compounds with x greater than or equal to 0.80 order ferromagnetically, whereas those with x less than or equal to 0.20 exhibit metamagnetic behaviour characteristic for antiferrom agnets like UNiAl. The initial Pt (Ir) substitutions lead to an increase (d ecrease) of the Neel temperature whereas the critical field for metamagneti sm becomes gradually reduced in both cases. The electronic specific-heat co efficient gamma is strongly reduced in UNi1-xPtxAl (from 164 to 113 mf mol( -1) K-2 for x increasing from 0 to 0.2) and enhanced in UNi1-xIrxAl (up to 198 mJ mol(-1) K-2 for x=0.2). The obtained results are discussed in the co ntext of the effects induced by substitutions of other transition metals in UNiAl considering the evolution of the 5f-d hybridization. (C) 1999 Elsevi er Science S.A. All rights reserved.