Superconductivity and Magnetism in UPt3

We describe ninon spin rotation/relaxation (μSR) measurements of UPt3. In zero applied field, we find that a spontaneous field appears below the lower superconducting transition and is visible when the initial muon polarization is both along the ĉ axis and in the basM plane. In addition, we have measured the muon Knight shift for fields in both primary directions. We find that the Knight shift decreases within the superconducting state for fields along ĉ, as well as for a field of 1 T in the basal plane.