Superconductivity and magnetism in UPt3

We describe muon 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 theĉ axis and in the basal 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 alongĉ, as well as for a field of 1 T in the basal plane.