Field-induced change of the antiferromagnetic structure of UNiAl

UNiAl, which orders below T-N = 19.3 K antiferromagnetically (AF), exhibits pronounced magnetic-history-dependent phenomena. This concerns all bulk magnetic properties and also the microscopic magnetic structures. When a magnetic field larger than 7-8 T is applied along the c-axis at temperatures below 7 K, the zero-field-cooled AF structure characterized by a propagation vector (0.1,0.1,0.5), is transformed into a new AF structure with a propagation vector (0.173. 0, 0.5) that persists down to zero field. Uranium moments are in both structures sine-wave modulated with a similar magnitude of 1.2-1.3mu(B)/U, however, the modulation is in different directions. Effective Ni-mediated interactions along distinct chains of ions are likely responsible for the change in the basal-plane component of the propagation vector. (C) 2002 Elsevier Science B.V. All rights reserved.