Publications in Scientific Journals:

H. Michor, St Berger, M. El-Hagary, C. Paul, E. Bauer, G. Hilscher, P. Rogl, G. Giester:
"Crystal structure and Kondo lattice behavior of CeNi9Si4";
Physical Review B, 67 (2003), 224428-1 - 224428-10.

English abstract:
Crystal structure and Kondo lattice behavior of CeNi9Si4

H. Michor, St. Berger, M. El-Hagary, C. Paul, E. Bauer, and G. Hilscher Institut für Festkörperphysik, Technische Universität Wien, Wiedner Hauptstrasse 8?10, A-1040 Wien, Austria

P. Rogl Institut für Physikalische Chemie, Universität Wien, Währingerstrasse 42, A-1090 Wien, Austria

G. Giester Institut für Mineralogie und Kristallographie, Universität Wien, Althanstrasse 14, A-1090 Wien, Austria

(Received 20 January 2003; published 20 June 2003)

We have studied the crystal chemistry and magnetic, thermodynamic, and transport properties of RNi9Si4 with R = La and Ce. These compounds crystallize in a fully ordered tetragonal (space group I4/mcm) variant of the cubic NaZn13 type. The low-temperature properties characterize CeNi9Si4 as a Kondo lattice with a large Sommerfeld value [gamma] = 155(5) mJ/mol K2 as compared to [gamma] = 33 mJ/mol K2 of Pauli paramagnetic LaNi9Si4. The temperature dependencies of the specific heat and susceptibility are well described by the degenerate (J = 5/2) Coqblin-Schrieffer model with a characteristic temperature T0 [~=] 180 K. The large Ce-Ce spacing in CeNi9Si4 (dCe-Ce [[approximate]] 5.6 Å) implies very weak Ce-Ce intersite exchange interactions which is corroborated by the thermoelectric power S(T) showing close agreement with theoretical results of the degenerate Anderson lattice without intersite interactions. CeNi9Si4 appears to be a model type Kondo lattice system with T0> [Delta] CEF [>>] TRKKY where T0, [Delta] CEF (crystalline electric field), and TRKKY (Ruderman-Kittel-Kasuya-Yosida) are the characteristic energy scales of the Kondo interaction, crystal field splitting, and Ce-Ce intersite exchange coupling, respectively. CeNi9Si4 shows a remarkably low ratio A/ [gamma] 2 = 0.83 (8)10?6 [Omega] cm(molK/mJ)2 which is one order-of-magnitude smaller than the usual Kadowaki-Woods ratio of heavy-fermion systems. 2003 The American Physical Society

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