Magnetic structure of UPt

We have determined the magnetic structure of the 30 K ferromagnet UPt using neutron powder diffraction. The ferromagnetic structure consists of alternating layers of magnetic and non-magnetic uranium atoms on which is superimposed a non-colinear antiferromagnetic structure which itself reorders at 20 K. The ferromagnetic moments are aligned in the crystallographic b direction and agreement with experimental magnetization data is good. The complexity of the magnetic structure implies that delocalization of the uranium moments is not required to explain the loss of magnetism at high pressure.