Using magnetic x-ray and neutron diffraction in UP${\mathrm{t}}_3$, we find that a suppression of the antiferromagnetic scattering intensity in the superconducting phase is due to a reduction in the magnitude of the staggered moment with no change in symmetry. The existence of the suppression as well as the magnetic correlation lengths are not affected by the presence or absence of a visible splitting in the superconducting transition. The simplest models wherein antiferromagnetic order provides the symmetry-breaking field for the splitting do not provide a compete explanation of our results.

• Received 16 January 1995

DOI:https://doi.org/10.1103/PhysRevLett.75.1178