Magnetic structure of U2Pt2Sn

U2Pt2Sn forms in a ternary derivative version (space group P4(2)/mnm) of th e tetragonal U3Si2-type of structure. Clear anomalies in the magnetic susce ptibility, specific heat and electrical resistivity around 15 K and their c hanges in magnetic fields indicate antiferromagnetic ordering below this te mperature. The antiferromagnetic ground state of U2Pt2Sn is corroborated by the metamagnetic transition observed in the magnetization around 22 T meas ured at 4.2 K and by magnetic reflections in the neutron-powder diffraction pattern at low temperatures. The U moments of 1.16 +/- 0.07 mu(B)/U form a complex incommensurate non-collinear magnetic structure. The moments are c onfined to (1 1 0)-type of planes and tilted from the c-axis by 60 degrees. Moreover they are sine-wave modulated along the tetragonal axis with a pro pagation vector q = (0, 0, 0.1823). (C) 1999 Published by Elsevier Science B.V. All rights reserved.