Magnetic structure of UPd2Si2 in a magnetic field

Elastic neutron-scattering and magnetization measurements have been performed on a single crystal of UPd2Si2 in fields along the c axis. In zero field there is a simple body-centered antiferromagnetic structure for temperatures up to 108 K. Between 108 K and the Néel temperature there is an incommensurate longitudinal spin-density-wave phase. For fields above 1.9 T, a new phase appears that separates the two zero-field phases. The new phase …