Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 35: Correlated Electrons - Quantum Critical Phenomena

TT 35.4: Talk

Wednesday, March 9, 2005, 12:00–12:15, TU H104

Magnetization dynamics of YbIr₂Si₂ — •Arno Hiess¹, Oliver Stockert², Michael M. Koza¹, Zakir Hossain³, and Christoph Geibel² — ¹ILL, Grenoble, France — ²MPI-CPfS, Dresden, Germany — ³IIT, Kanpur, India

Several intermetallic compounds containing cerium, ytterbium or uranium exhibit deviation from Landau-Fermi-liquid behaviour when tuned through a magnetic instability by means of a control parameter such as doping, hydrostatic pressure or magnetic fields. Within this class of compounds YbIr₂Si₂ occupies a special place as it exists in two crystallographic modifications: one (P-type) showing antiferromagnetic order below 0.7 K, the other (I-type) remains paramagnetic down to lowest temperatures. We here report on inelastic neutron scattering experiments investigating the magnetization dynamics in the paramagnetic state of both modifications. Magnetic scattering has been identified for energy transfers smaller 40meV. Surprisingly, only the I-type modification shows two well-resolved crystal-field transitions whereas for the magnetically ordered P-type modification a broad (most-probable quasi-elastic) signal is observed. We discuss these observations in terms of the crystallographic local ytterbium site symmetry as well as in respect to their unusual thermodynamic (electronic) properties.