Crystal structure and magnetic behaviour of UCoAs2

A new uranium compound UCoAs2, has been prepared and studied by means of si ngle-crystal X-ray diffraction and magnetic measurements. It crystallises w ith the tetragonal HfCuSi2-type structure (s.g. P4/nmm) and the lattice par ameters: a = 3.9615(6) Angstrom and c = 9.149(2) Angstrom. The compound ord ers ferromagnetically at 150(3) K with a spontaneous magnetic moment of abo ut 1.8 mu(B). The magnetic behaviour in UCoAs2 exhibits a giant anisotropy in both the ordered and the paramagnetic region. This feature we interpret as being caused predominantly by strong f-d hybridisation and pronounced cr ystal field effect. (C) 2000 Elsevier Science S.A. All rights reserved.