A. Grauel

Heavy-fermion superconductivity atT c =2K in the antiferromagnet UPd2Al3

UPd2Al3 is a new heavy-fermion superconductor with a recordTc of 2 K. In addition, it shows a transition to long-range antiferromagnetic order atTN=14 K. Its Sommerfeld coefficient is reduced from γp=210mJ/K2 mole in the paramagnetic to γ0=150mJ/K2 mole in the antiferromagnetic phase.

A new heavy-fermion superconductor: UNi2Al3

Measurements of the resistivity, susceptibility and specific heat are reported which clearly show that the hexagonal compound UNi2Al3 is a heavy-fermion magnet belowTN=4.6 K and a heavy-fermion superconductor belowTc=1 K.

Neutron diffraction study of the heavy fermion superconductors UM2Al3(M=Pd, Ni)

An elastic neutron scattering study was performed on the new superconducting heavy fermion systems UPd2Al3 and UNi2Al3. The neutron diffraction patterns reveal unambiguously long range antiferromagnetic order in UPd2Al3 with an ordered magnetic momentμU = (0.85±0.03)μB, which coexists with the superconducting state. This is by far the largestμU value observed for any heavy fermion superconductor. For UNi2Al3, no long-range magnetic order could be observed for temperaturesT≧1.5 K, yielding an upper limit of the ordered moment of 0.2μB.

UPd2Al3-a new heavy-fermion superconductor with Tc = 2K

Abstract We report measurements on polycrystalline and, for the first time, single-crystalline samples of UPd2Al3, a new heavy-fermion superconductor (HFS) with a record-Tc of 2K and an antiferromagnetic transition at TN = 14K.

4f-conduction electron hybridization in ternary CeTMAl compounds

Abstract We present an investigation of CeTMAl phase diagrams with TMRu, Pd, Pt and Au. Several new compounds have been characterized by measurements of the electrical resistivity ϱ ( T ), the do susceptibility χ ( T ) and, in some cases, the specific heat C ( T ). We find that in the compounds with TMRu, the hybridization strength between 4f and conduction electrons is strong, leading in most compounds to an intermediate valent (IV) state. By contrast, most of the investigated compounds with TMPd, Pt and Au order magnetically indicating a much weaker hybridization strength. However, some of the Pt and especially Pd compounds are very near to the crossover from the magnetic to the non-magnetic regime as deduced from a Kondo-type maximum in the resistivity and a large electronic specific heat at low temperatures.

Magnetic ordering in the heavy-fermion compounds CePtSi2 and CeNiGe2

Abstract The ground state of three CeTMX 2 compounds with CeNiSi 2 structure type was investigated by electrical-resistivity, magnetic-susceptibility and specific-heat measurements. Whereas CeNiSi 2 is an intermediate-valent system, we observe in CePtSi 2 and CeNiGe 2 magnetic ordering in the presence of heavy fermions. The trends in heavy-fermion formation on going from either the 111 or 122 to the 112 compounds are discussed.

Ground state properties of UNi2Al3 and UPd2Al3

Abstract We present a status report on our investigation of the two new heavy fermion superconductors UNi 2 Al 3 and UPd 2 Al 3 . We discuss in particular the magnetic phase diagram, crystal field effects and the properties of the superconducting state.

Alloying-induced transition from local-moment to itinerant heavy fermion magnetism in Ce(Cu1−xNix)2Ge2

Abstract A monotonous increase of the Kondo temperature in Ce(Cu1−xNix)2Ge2 from 7 (x = 0) to 30 K (x = 1) is accompanied by drastic changes of ground state properties: for x⩽0.2, a modulated magnetic structure (q01 = (0.28, 0.28, 0.54)) involving Kondo-reduced local Ce moments ( μ s = 0.74μ B Ce for x = 0) forms below TN1(x). TN1 = 4. 1 K for CeCu2Ge2 is strongly depressed upon increasing x. At x ≲ 0.2, a different modulation develops below TN2(x) which becomes maximum (≃4 K) for x = 0.5. Since this is characterized by a very small value of q02 (=(0, 0, 0.13) at x = 0.5) and a gradually decreasing ordered moment (reaching μs ≲ 0.2μB/Ce for x ⩾0.65), we ascribe it to “heavy fermion band magnetism”. For 0.02⩽x⩽0.3, the two modulations seem to be superposed at sufficiently low temperatures. A non-magnetic heavy fermion ground state exists for x > 0.75.

Phase transitions in the heavy Fermi-liquid state: CeCu2Si2, UNi2Al3 and UPd2Al3

Abstract We discuss the superconducting and other phase transitions in CeCu 2 Si 2 and UT 2 Al 3 (T: Ni,Pd). For CeCu 2 Si 2 , a novel lattice instability is found to limit the highest T c attainable by appropriate heat treatment. In the UT 2 Al 3 homologs, antiferromagnetism develops at T N = 4.6K (14K) and possibly coexists with heavy-fermion superconductivity below T c = 1K (2K) for T = Ni(Pd).

Crystalline structure of the strontium niobates Sr4Nb2O9 and Sr5Nb4O15

Abstract The strontium niobate compounds Sr 4 Nb 2 O 9 and Sr 5 Nb 4 O 15 were prepared by solid state reactions and studied by high-resolution X-ray powder diffraction measurements. The structures of the two systems Sr 4 Nb 2 O 9 and Sr 5 Nb 4 O 15 were obtained by Rietveld analysis, indicating triclinic and monoclinic unit cell parameters, respectively. Both structures reveal a layering of Sr O planes. The Nb ions are located in octahedral holes between the Sr O layers.