ANTIFERROMAGNETIC ORDER IN UPT3 UNDER PRESSURE - EVIDENCE FOR A DIRECT COUPLING TO SUPERCONDUCTIVITY

We use neutron diffraction to study the effect of hydrostatic pressure on the ordered antiferromagnetic moment in the heavy-fermion superconductor UPt3. It is found that hydrostatic pressure suppresses and eventually destroys the antiferromagnetic order. A comparison of our results with specific-heat measurements made under hydrostatic pressure shows that the splitting of the two anomalies in the low-temperature heat capacity correlates well with the collapse in the magnitude of the ordered moment. This suggests a coupling between the superconducting and antiferromagnetic order parameters.