Change of the effective spin degeneracy in CeNi_9−xCu_xGe₄ due to the interplay between Kondo and crystal field effects

¹ CPM, Institut für Physik, Universität Augsburg - 86159 Augsburg, Germany, EU
² Institut für Festkörperphysik, Technische Universität Wien - 1040 Wien, Austria, EU
³ Forschungsneutronenquelle Heinz Maier-Leibnitz, Technische Universität München - 85747 Garching, Germany, EU
⁴ Strukturforschung, Materialwissenschaft, Technische Universität Darmstadt - 64287 Darmstadt, Germany, EU
⁵ ISIS Facility, Rutherford Appleton Laboratory - Chilton, Didcot OX11 0QX, UK, EU
⁶ Max-Planck-Institut CPfS - 01187 Dresden, Germany, EU

^a ludwig.peyker@physik.uni-augsburg.de

Received: 23 June 2010
Accepted: 19 January 2011

Abstract

Elastic and inelastic neutron scattering experiments were carried out on the heavy-fermion systems CeNi_8.6Cu_0.4Ge₄ and CeNi₈CuGe₄ to study i) the influences of Ni/Cu substitution on the crystal field parameters and to identify ii) the driving forces of quantum criticality in CeNi_9−xCu_xGe₄. The relevance of competing RKKY and Kondo interactions and changes of the crystal field parameters is discussed. The crystallographic site where the Ni replacement by copper atoms takes place is identified by neutron powder diffraction studies. Furthermore, quasi-elastic and inelastic neutron scattering studies provide detailed information regarding the Kondo properties and the changes of the crystal field parameters resulting from the Ni/Cu replacement. Hence, a reduction of the effective spin degeneracy of the crystal field ground state with increasing Cu concentration is identified as one important control parameter of quantum criticality in CeNi_9−xCu_xGe₄. The results of these experiments are complemented by measurements of the thermopower.