Specific heat and magnetization studies in UPt 3 and UBe 13 at very low temperatures

Abstract

We have measured the specific heat capacity of a single crystal of UPt 3 in zero magnetic field and in 2 T, just above B c2, with the adiabatic warm-up method down to a final temperature of 15 mK. The results prove our previous assumption that in the normal state of UPt 3 there exists a similar but modified specific heat anomaly around 20 mK as in the superconducting state. Entropy balance between both states is fulfilled if one includes the low temperature peaks. For UBe 13 we find no indication of such a specific heat anomaly down to 35 mK. Dc-magnetization measurements in a SQUID system with B//c show a temperature dependence of the London penetration depth in UPt 3 changing from a T x -law with x=3.2−3.7 at higher temperatures to a T 2-law below 150 mK, extending down to 20 mK. Magnetic field sweeps up to B c2 resulted in strong sudden heating, predominantly around the thermodynamical critical field (Bean-Livingston effect) but also at higher field values.