Resonant magnetic x-ray scattering study of phase transitions in UPd2Al3

Resonant magnetic x-ray scattering measurements were performed on a single microcrystallite at the surface of a polycrystalline boule of the antiferromagnetic, heavy fermion superconductor UPd2Al3. These measurements show a strong anomaly in the order parameter at 11.8 K, below TN∼14.5 K, indicating at least two antiferromagnetically ordered phases which share a common periodicity. Measurements performed at temperatures near and below Tc=2.0 K show the antiferromagnetic order parameter to be unaffected on passing into the superconducting phase, to ±2%.