ON THE MAGNETIC AND SUPERCONDUCTING PHASES OF HEAVY-FERMION UPT3

The electronic instability in the highly correlated electron system UPt3 gives rise to various intriguing phenomena at liquid-helium temperatures, among which the occurrence of unconventional superconductivity (T(c)+ = 0.49 K, T(c)- = 0.44 K) has attracted most attention. In a magnetic field three superconducting phases are observed that meet at a tetracritical point. We here present a discussion of a number of puzzling aspects of a superconducting phase diagram (B perpendicular-to c) of unprecedented accuracy, determined by dilatometry. The possible interplay of superconductivity and reduced moment antiferromagnetism (T(N) = 5 K) is investigated. Furthermore, we report on recent studies of the suppression of T(c), by alloying with Pd, Y, Th, Au and Ir.