COMMENSURATE AND INCOMMENSURATE MAGNETIC ORDER OF UPDSI

UPdSi was studied by the neutron powder diffraction. It crystallises w ith the orthorhombic TiNiSi-type structure and exhibits two magnetic p hase transitions (27 and 33 K). The ground state is commensurate antif erromagnetic with q = (0.25, 0, 0.25). U moments (1.40 mu(B), at 3.5 K ) are oriented along the b-axis. Between 27 and 33 K we observe an inc ommensurate phase with q(inc) = (delta, 0, delta). At 31 K, delta = 0. 217 and mu(U) = 0.65 mu(B) parallel to b. (C) 1998 Elsevier Science B. V. All rights reserved.