Magnetic properties of the UCo1-xNixAl system

We have measured the DC-and AC-magnetic susceptibility on the pseudoternary 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 assuming that the Ni-atoms first occupy the (1b)-sites up to x similar to 0.3 and then the (2c)-sites. Substitution of Co with small amounts of Ni in UCoAl(x < 0.1) leads to a disappearance of a magnetic ordering. Below 15 K these compositions exhibit a metamagnetic transition in magnetic fields. In the composition range 0.1 < x < 0.5, there exist ferromagnetic correlations between U-moments at low temperatures, weakening with increasing x. Hence, the compositions x = 0.5-0.7 are paramagnetic to the lowest temperature measured (1.7 K). On the Ni-rich side of compositions (x greater than or equal to 0.8), the antiferromagnetic state sets in. For these alloys, the susceptibility anomaly related to the Neel temperature, increases from 3 to 23 K, being highest for UNiAl. (C) 1997 Elsevier Science S.A.