Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 20: Poster:Schichten(1-29),Spintrsp(30-45),Ex-Bias(46-63),Spindyn(64-75),Mikromat.(76-80),Cluster(81-94),Abbv.(95-99),Obflm(100-02),SpElek.(103-09),E-Theo(110-14),Mikromag.(115-16),Spin+PÜ(117-26),Mag.Mat.(127-51),Meth.(152-55),Mol.Mag(156-59),Kondo(160-65

MA 20.162: Poster

Montag, 7. März 2005, 14:00–18:00, Poster TU C

New clathrate-like compounds EuPd₅P₂ and EuPd₁₂P₅ — •Ulrike Köhler, Sergij Budnyk, Silke Paschen, Frank Steglich, and Yuri Grin — MPI für Chemische Physik fester Stoffe, Nöthnitzer Straße 40, 01187 Dresden

Many filled cage compounds are known to have low phonon thermal conductivities κ_ph. In Kondo insulators the hybridization between localized 4f states and a conduction band is held responsible for the formation of a narrow band gap at the Fermi level and hence for a semiconductor-like electrical resistivity ϱ and a low electronic thermal conductivity κ_el. The strong energy dependence of the quasiparticle density of states near the Fermi level in these materials gives rise to high values of the thermopower S. Since a good thermoelectric material is characterized by a high thermoelectric figure of merit ZT = TS²/[ϱ(κ_ph + κ_el)], Kondo insulating filled cage compounds appear to be a promising class of new materials. In this contribution we present physical properties of the two newly discovered filled cage compounds EuPd₅P₂ and EuPd₁₂P₅ which crystalize in a novel clathrate-like structure. Both materials have a metal-like ϱ(T) and are therefore expected to show neither high S(T) nor low κ_el(T). The high temperature magnetic susceptibility χ is well described by a Curie-Weiss law with a full Eu²⁺ effective moment. Below 10 K both compounds order magnetically. The large Eu-Eu distance indicates that not the direct exchange interaction between the localized 4f moments but the RKKY interaction is responsible for the magnetic ordering.

Modifications of the compounds investigated here will be necessary to make them good thermoelectrics.