On the superconducting phase transitions of UPt₃

The possible role of antiferromagnetic order in causing a multiplicity of superconducting phase transitions in UPt₃ is investigated. Two results are presented which shed light on this question. First, a small hydrostatic pressure is found to have a significant effect on both 1) the neutron scattering intensity of the antiferromagnetic Bragg peak, which is more than halved by 2 kbar, and 2) the H_c2(T) curve, from which the kink — regarded as a signature of phase multiplicity — disappears above 1.5 kbar. Secondly, the kink in H_c2(T) is observed for all field directions within the basal plane. This evidence is discussed in connection with current theories.