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TT: Fachverband Tiefe Temperaturen

TT 6: Postersession Correlated Electrons: (General) Theory, Low-Dimensional Systems, Kondo Physics, Heavy Fermions, Quantum-Critical Phenomena

TT 6.59: Poster

Montag, 23. März 2009, 13:00–16:45, P1A

^{121, 123} Sb magnetic resonance as a local probe for gap formation in FeSb₂ — •Michael Baenitz¹, Andrei Gippius², Simon Johnsen³, Bo Iversen³, and Frank Steglich³ — ¹Max-Planck Institut for Chemical Physics of Solids, Dresden, Germany — ²Faculty of Physics, Moscow State University, Moscow, Russia — ³Department of Chemistry, University of Aarhus, Denmark

There is a revived interest on FeSb₂ after classifying this system as the second Fe containing Kondo insulator after FeSi. The formation of a spin and charge gap out of an enhanced density of states N(E_F) is one of the key features of these materials. Furthermore FeSb₂ surprisingly shows a colossal Seebeck coefficient around 10 K. Here we report on a comparative study on FeSb₂ and its structural homologue RuSb₂. For both compounds we found two regimes in the temperature dependence of ¹²³(1/T₁). Above 40 K (HT) a conventional activated behavior (with D/k_B @ 450 K for FeSb₂) dominates in 1/T₁. Below 40 K (LT) in both systems an unconventional 1/T₁ behavior with a smooth maximum at 10 K is observed. To analyze this behavior we propose the presence of T-dependent in-gap states forming a narrow band of localized spins with S = 1/2 near the bottom of the conduction band. This model enables us to fit the ¹²³(1/T₁) data in the entire temperature range (LT + HT) for FeSb₂. Furthermore the relevance of these in-gap states for the colossal Seebeck effect is discussed.