Ultrasound measurements of the B-T diagram of the heavy-fermion material UPt3 in very high magnetic fields

We present elastic constant measurements of the heavy-fermion superconductor UPt(3) at temperatures down to 50 mK and in static magnetic fields up to 30 T. These experiments yield information about the metamagnetic (MM) transition itself as a function of field as well as about the accompanying transitions as a function of temperature both above and below the critical field B* = 20.5 T. A comparison is made with analogous measurements in CeRu(2)Si(2). Moreover, we present new results on the region of the antiferromagnetic spin density wave (AF-SDW) in the B-T plane and its anisotropy with respect to the direction of the magnetic field. Here a comparison with the anisotropy of the superconducting critical fields gives clues about the interaction of superconductivity and magnetism in UPt(3).