ANTIFERROMAGNETIC STRUCTURE OF UNIAL

UNiAl crystallizes in the hexagonal ZrNiAl-type structure. Magnetic, t ransport, and thermal properties of UNiAl point to an antiferromagneti c (AF) ordering below T-N= 19.3 K. Below this temperature UNiAl orders with propagation vector q=(0.1,0.1,0.5). U magnetic moments are orien ted along the hexagonal axis and modulated sinusoidally within the bas al plane. The modulation is not even partially squared-up down to 1.7 K. The maximum size of U moment is (1.24+/-0.03)mu(B)/U. However, the three U atoms that are crystallographically equivalent do not carry th e same moment within the crystallographic unit cell. The propagation v ector of AF structure does not change in the whole temperature range. AF correlations that propagate also with q =(0.1,0.1,0.5) can be trace d at temperatures up to 30 K showing the critical scattering near T-N. [S0163-1829(98)02529-6].