Talks and Poster Presentations (without Proceedings-Entry):

H. Michor, E. Bauer, St Berger, C. Dusek, E. Idl, G. Hilscher, P. Rogl, A. Schindler, R. König, U. Killer, E. Scheidt:
"Heavy-Fermion and NFL-behaviour CeNi9X4 (X=Si, Ge)";
Talk: 6th Prague Colloquium on f-electron systems, Charles University, Prague, Czech Republic; 2002-07-05 - 2002-07-09.

English abstract:
Heavy-Fermion- and NFL-behaviour in CeNi9X4 (X=Ge, Si)
H. Michor1, E. Bauer1, St. Berger1, C. Dusek1, E. Idl, G. Hilscher1,
P. Rogl2, A. Schindler3, R. König3, U. Killer4 und E.-W. Scheidt4

1Institut für Festkörperphysik, TU Wien, Austria,
2Institut für Physikalische Chemie, Universität Wien, Austria
3 Physikalisches Institut, Universität Bayreuth, Germany
4 Lehrstuhl für Experimentalphysik III, Universität Augsburg, Germany

The compounds CeNi9X4 (X = Ge, Si) have a tetragonal crystal structure (space group I4/mcm) that is derived from the cubic NaZn13 structure type. In the case of CeNi9Si4 resistivity, magnetic susceptibility and specific heat measurements reveal Kondo-lattice behaviour with a T2 temperature dependence of the electrical resistivity (A~0.01 mWcm/K2) as well as a Sommerfeld value g = 160 mJ/molK2. The Kadowaki-Woods ratio A/g2~0.4x10-6 mWcm(molK/mJ)2 indicates weak RKKY coupling and a non-magnetic ground state. The magnetic contribution to the specific heat is well described by the Coqblin-Schrieffer model with an effective J=5/2 ground state and a characteristic temperature T0 180K.
CeNi9Ge4 on the other hand, exhibits non-Fermi liquid (NFL) properties, i.e. an approximately logarithmic divergence of the low temperature heat capacity C(T)~- T ln T in the temperature range 80 - 1000 mK, indicating the proximity of a quantum critical point. Hydrostatic pressure and magnetic field recover the Fermi-liquid state. Furthermore, resistivity measurements down to 5 mK show a cross-over from

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