[en] In the reporting year 1990, the following project work has been continued: (1) Thermal dilatation measurement in La₂CuO_4+δ, La_2-xSr_xCuO₄, La_2-xBa_xCuO₄ and YBa₂Cu₃O_7-δ. (2) Determination of specific heat capacity and of thermal conductivity of YBa₂Cu₃O_7-δ at low temperatures and high magnetic fields. (3) Optimization of the superconducting properties of Nd_2-xCe_xCuO_4-δ. (4) X-ray absorption spectroscopy analysis of Nd_2-xCe_xCuO_4-δ and Sm_2-xCe_xCuO_4-δ. (orig.) With 7 figs

[en] Short note. 2 refs

No abstract available

[en] Heavy-fermion (HF) phenomena occur in f-electron compounds usually in the vicinity of long-range antiferromagnetic (AF) ordering which forms below T_N. Near a 'magnetic instability' where T_N→0, low-lying and spatially extended AF spin fluctuations of large amplitude are usually considered to be the cause for an unconventional normal state and, sometimes, for superconducting low-T states. By discussing a number of prototypical stoichiometric compounds (CeCu₂Si₂, CeNi₂Ge₂ and YbRh₂Si₂) we will argue that, in addition to the itinerant AF spin fluctuations, local f-degrees of freedom may play an essential role for the above phenomena. Compared to the cuprate superconductors, their HF counterparts behave strikingly non-universally

[en] The dynamical susceptibility of single crystals of the isostructural metallic systems (Ce/sub x/La/sub 1-x/)Al₂ and (Ce/sub x/Y/sub 1-x/)Al₂, 0.07 less than or equal to x less than or equal to 1, has been measured by neutron scattering between 2 and 300⁰K. The energy spectra are analyzed in terms of quasielastic and inelastic lines of finite widths. The results are compared with resistivity and thermopower data on dilute (Ce/sub x/(La/sub 1-z/Y/sub z/)/sub 1-x/)Al₂ alloys (x less than or equal to 0.15, z less than or equal to 1). 3 figures

No abstract available

No abstract available

[en] Results are presented for the electronic Lorenz ratio of two annealed (La,Ce)Al₂ alloys with different Ce concentrations over the temperature range 0.5-10K. The observed dependence confirms reasonably well the elastic nature of the Kondo scattering process. (Auth.)

[en] Specific heat measurement on CeAl₂ show that in this compound the Kondo effect is of comparable strength (ksub(B)Tsub(K)) to the Ce-Ce interactions which yield magnetic order below Tsub(N) approximately = 4 K. Tsub(K) approximately = 6 K is estimated from (a) the fact that the large specific heat coefficient γ magnetic field up to 5 T, and (b) from the specific heats of (Cesub(x)Lasub(1-x)Al₂ alloys. (Auth.)

No abstract available