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We have measured the dc magnetization of three high-quality single crystals of UPt 3 with a SQUID magnetometer down to ഠ5 mK in magnetic fields below 2 mT. With B in theĉ direction we find a double superconducting transition, while for B kâ we observe only one. At lower temperatures the temperature dependence of the magnetization follows power laws indicating unconventional behavior for the penetration depth. Below 20 mK a steep diamagnetic drop occurs, coinciding with the specific heat anomaly which we found earlier at 18 mK, pointing to static antiferromagnetic order.

Recently, a superconductive reference device, SRD1000, with ten reference materials has been developed to enable simplified in situ calibration of interpolating thermometers. We report on the evaluation of SRD1000 prototypes at various laboratories. The devices were built and tested by HDL and KOL, calibrated at NMi-VSL and then distributed to other partners where they were re-calibrated against the local realisations of the PLTS-2000 or laboratory scales. As a result, we obtained data on the superconductive transition temperatures, widths and shapes for four different devices. Reproducibility, sharpness of the transitions, supercooling and sensitivity to magnetic fields are evaluated. This leads to estimates of the uncertainty in determination of the transition midpoint and temperature.

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