Resistivity of single-crystalline UPt3 and its pressure dependence; Interpretation by a spin-fluctuation model

Resistivity measurements on a series of uranium-platinum compounds were carried out in the range 1.3 up to 300 K and pressures up to 5 kbar. The resistivity of single-crystalline UPt₃ is strongly anisotropic and points to pronounced spin-fluctuation effects that are partly suppressed at a pressure of 4 kbar. In paramagnetic UPt₂ and UPt₅ spin-fluctuation effects are less pronounced, whereas in ferromagnetic UPt the spin-disorder scatter is dominant above 27 K.     

Field induced moment-reorientation transitions in hexagonal ferrimagnets

It is shown that the basal plane anisotropy in a hexagonal easy-plane ferrimagnetic 3d-4f system yields discontinuities in the magnetisation curve for external fields applied in the easy plane. These discontinuities are believed to be the origin of the anomalously large high-field susceptibility in the Dy₂Fe_17?yAl_y compounds. At the discontinuities First-Order Moment-Reorientati on (FOMR) transitions occur. They are governed by the basal plane anisotropy and take place in the easy plane as a result of a competition between the exchange and the magnetostatic energies of the two sublattice magnetisations. The moment reorientation process should be taken into consideration even at low fields in the case of a small difference between the two magnetisation values. The transition fields give a direct method to evaluate the exchange coupling between the 3d and 4f spins.     

Upper critical fields of single-crystalline and polycrystalline Ca-Sr-Bi-Cu-O compounds

The ac resistivity of a 110 K phase multiphase polycrystalline Ca-Sr-Bi-Cu-O compound and an 85 K phase single-crystalline Ca_0.9Sr_2.1Cu_2.0O_{8 +} has been measured in various magnetic fields up to 8 T. Values forB _c ^2/ (0) of 71.5 T and forB _c2 (0) of 542 T are found for the 85 K phase sample. A value forB _c2(0) of 57.9 T is estimated for the 110K phase compound.     

Upper critical magnetic fields of the heavy fermion superconductors CeCu2Si2, UPt3, and UBe13: Comparison between experiment and theory

We report measurements of the upper critical magnetic field,B _c2 (T), on single crystal and polycrystalline samples of the heavy-fermion superconductors CeCu₂Si₂, UPt₃ and UBe₁₃. Comparison is made with experimental results for a conventional superconductor (CeRu₃Si₂) and with results of the weak-coupling theory applied to both ans-wave superconductor in the dirty-limit and ap-wave superconductor. New anomalies are discovered to add to the unusualB _c2 (T) behavior.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

A rheological and structural study of a discotic side chain polymer solution

The structural and dynamical properties of a physical network in a discotic side-chain polymer solution have been studied. For that purpose, use has been made of rheological measurements and a statistical network model for the crosslinking of polymer. The goal of the investigation was to gain more insight into processes playing important roles in the subtle interactions between discotic side-chain polymers. A relatively simple mechanical model is presented to describe the mechanical behaviour of the solutions. Moreover, results are shown for the specific dynamic as well as structural properties of the physical networks in these solutions.