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TT: Tiefe Temperaturen

TT 8: Correlated Electrons: Heavy Fermions

TT 8.5: Vortrag

Montag, 27. März 2006, 15:30–15:45, HSZ 301

Quasi quartet CEF ground state with possible quadrupolar ordering in the tetragonal compound YbRu₂Ge₂ — •H. S Jeevan¹, Z Hossain², and C Geibel¹ — ¹MPI-CPfS Nöthnitzer Str. 40, 01187 Dresden, Germany — ²Department of Physics, I.I.T-Kanpur, 208016. India

In search for new Yb-base stoichiometric systems which are close to quantum critical point at ambient pressure, we have synthesized and investigated single crystals of YbRu₂Ge₂, an homologue of YbRh₂Si₂. From the systematic of the known YbM₂X₂ (M = d elements, X = Si, Ge) we had hoped that this compound will be nonmagnetic and located close to a QCP. But surprisingly we found that in YbRu2Ge2, Yb is in a stable trivalent state and present some kind of ordering at a much higher temperature Tm =10K then in presently known Yb-compounds. High temperature magnetic susceptibility follows Curie-Weiss behavior with effective moment very close to that expected for trivalent Yb ions. Low temperature susceptibility exhibits a peak at ~6 K presumably due to antiferromagnetic type of order. Resistivity linearly decreases with temperature down to about 50 K, then increases with further decreasing temperature due to Kondo interaction, passes though a maximum at 10 K below which the resistivity undergoes a rapid decrease due to freezing out of spin disorder scattering. The Specific heat of YbRu₂Ge₂ shows two large peaks, one at 10K and another at 6K, the low temperature anomaly corresponding to the antiferromagnetic transition as detected by chi(T). The nature of the high temperature anomaly in specific heat is under investigation.