Antiferromagnetic structure of UNiAl

Abstract

UNiAl crystallizes in the hexagonal ZrNiAl-type structure. Magnetic, transport, and thermal properties of UNiAl point to an antiferromagnetic (AF) ordering below ${T}_{N}=19.3\mathrm{K}.$ Below this temperature UNiAl orders with propagation vector $\mathbf{q}=(0.1,0.1,0.5).$ U magnetic moments are oriented along the hexagonal axis and modulated sinusoidally within the basal plane. The modulation is not even partially squared-up down to 1.7 K. The maximum size of U moment is $(1.24\ifmmode\pm\else\textpm\fi{}0.03){\ensuremath{\mu}}_{B}/\mathrm{U}.$ However, the three U atoms that are crystallographically equivalent do not carry the same moment within the crystallographic unit cell. The propagation vector of AF structure does not change in the whole temperature range. AF correlations that propagate also with $\mathbf{q}=(0.1,0.1,0.5)$ can be traced at temperatures up to 30 K showing the critical scattering near ${T}_{N}.$