THE STRUCTURE AND MAGNETIC-MOMENT DISTRIBUTION IN THE ANTIFERROMAGNETIC PHASE OF U14AU51

The antiferromagnetic structure of the intermetallic compound U14Au51 has been determined from neutron polarimetric measurements and refined by combining these data with integrated intensity measurements. The s tructure was found to be non-collinear with the U moments confined to the a-b plane. The moments of U atoms in each of the two sets of sixfo ld sites are arranged hexagonally with rotations of 60 degrees between them and the two sets are rotated with respect to one another by 50 d egrees. The third (twofold) set of U atoms has no ordered moment. Thes e conclusions are in disagreement with a previous determination of the structure from powder data which gave a collinear structure with mome nts parallel to the c axis. Magnetization measurements made on single crystals in the temperature range 300-2 K can be understood in terms o f a transition to a non-collinear easy plane antiferromagnetic structu re stable below 22 K. Polarized neutron measurements have been used to determine the contribution of each of the U sites to the susceptibili ty between 22 and 2 K. These show that of the two sixfold U sites, tha t with the smaller ordered moment contributes more than half of the to tal susceptibility. The twofold site, which is characterized by a smal l U-U separation, makes the smallest contribution.