A. L. Giorgi

Lower critical field of U0.97Th0.03Be13: evidence for two coexisting superconducting order parameters

Evidence is presented for the coexistence of two superconducting order parameters in U0.97Th0.03Be13 below Tcb = 0.26 K. Measurements of the lower critical magnetic field performed for the first time and published data on the specific heat prove that the lower transition in U0.97Th0.03Be13 is a superconducting transition below which a new order parameter adds to the one existing below Tca = 0.48 K. Our conclusion contrasts the picture where one order parameter is replaced by another one.

Seebeck coefficient of heavy fermion compounds

The thermoelectric power (TEP) of the magnetically ordered Kondo lattices CeCu2Ge2, CeCu4Al8 and CePb3 was measured up to 350 K and compared with that of heavy-fermion UBe13. New low-T TEP-anomalies, presumably coherence-derived, are found to show up in CePb3 and UBe13, but to be absent in U0.97Th0.03Be13.

Pressure dependences of the specific heats of UPt3, UBe13 and CeAl3

The specific heats of UPt3, UBe,3 and CeAl3 have been measured under pressures to ≈9 kbar. The densities of electronic states decrease sharply with increasing pressure. For UPt3 the spin fluctuation terms decrease with increasing pressure, suggesting a positive correlation with superconductivity. For CeAl3 there is a qualitative change in the temperature dependence of the specific heat.

Low temperature and high magnetic field study of UBe13, U0.97Th0.03Be13 and UBe12.94Cu0.06

The pronounced maxima in the resistivity,p(T), and specific heat,C(T), observed in UBe13 near 2 K are partially suppressed by both field and doping. Normal-state U0.97Th0.03Be13 and UBe12.94Cu0.06 exhibit remarkable upturns in their Sommerfeld coefficient γ(T)=C(T)/T below 0.5 K which are strongly depressed by a magnetic field. The additional specific heat anomaly that exists in U0.97Th0.03Be13 belowTc is not reflected by any feature in the measurements of the DC Meissner effect.

MAGNETISM OF ACTINIDE COMPOUNDS

Abstract Actinide compounds exhibit most of the known magnetic phenomena. Their properties are easily modified in intermetallic compounds. We present some new results on uranium ferromagnets and heavy fermion antiferromagnets and explain their implications. We show magnetic ordering in a high T c superconductor.

A neutron small angle scattering study of the onset of ferromagnetism in TiBe2-xCux alloys

Abstract The onset of ferromagnetic order in TiBe 2- x Cu x alloys, with x = 0.5, 0.4, 0.3, 0.2 and 0.15, has been examined using the technique of neutron small-angle scattering. The Curie temperature, T c , for these alloys has been determined from the temperature dependence of the magnetic critical scattering. A linear extrapolation of T c versus copper concentration yields a critical concentration for ferromagnetic order of x c = 0.05 ± 0.02. For the alloys with x = 0.4, 0.5 the lineshape of the magnetic critical scattering, at and above T c , is well explained by the Ornstein-Zernicke form of the spin correlation function. For the lower concentration alloys the exact form of the spin correlation function is still unclear.

Evidence for unconventional superconductivity in UPt3: Splitting of the specific heat anomaly at Tc

Abstract The specific heats of two samples of UPt3 have been measured in the vicinity of Tc. Both samples show specific heat anomalies sharper than any previously observed and two clearly resolved maxima. The results are interpreted as evidence of splitting of the transition and unconventional pairing.

Small angle neutron scattering from TiBe1.5Cu0.5

Abstract Metals on the verge of and just in the weakly magnetic state offer a unique test ground for current theories of itinerant magnetism. TiBe 1.5 Cu 0.5 becomes ferromagnetic below 27 K with a low temperature moment of 0.07μ B per average atom. Using the temperature and wavevector dependence of small angle neutron scattering data we have investigated the spectrum of low energy spin dynamics both in the magnetically ordered and disordered phases. Over the experimentally accessible range the low wavevector excitations are characterized by damped spin waves which evolve continuously into overdamped diffusive modes above T c .