MAGNETIC-PROPERTIES OF THE UCO1-XNIXAL SYSTEM

We have measured the DC-and AC-magnetic susceptibility on the pseudote rnary system UCo1-xNixAl in the composition range 0 less than or equal to x<1.0. AU the samples studied were single phase and crystallize in the hexagonal Fe,P-type structure. Such behaviour can be explained as suming that the Ni-atoms first occupy the (1b)-sites up to x similar t o 0.3 and then the (2c)-sites. Substitution of Co with small amounts o f Ni in UCoAl(x < 0.1) leads to a disappearance of a magnetic ordering . Below 15 K these compositions exhibit a metamagnetic transition in m agnetic fields. In the composition range 0.1 < x < 0.5, there exist fe rromagnetic correlations between U-moments at low temperatures, weaken ing with increasing x. Hence, the compositions x = 0.5-0.7 are paramag netic to the lowest temperature measured (1.7 K). On the Ni-rich side of compositions (x greater than or equal to 0.8), the antiferromagneti c state sets in. For these alloys, the susceptibility anomaly related to the Neel temperature, increases from 3 to 23 K, being highest for U NiAl. (C) 1997 Elsevier Science S.A.