Berlin 2005 – scientific programme
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TT: Tiefe Temperaturen
TT 12: Correlated Electrons - Spin Systems and Itinerant Magnets: Experiment
TT 12.5: Talk
Saturday, March 5, 2005, 11:45–12:00, TU H2053
Specific Heat, Electronic State and Einstein Phonon Modes of Filled Iron Antimony Skutterudites: MFe4Sb12 (M = Na, K, Ca, Ba, La, Yb) — •W. Schnelle, H. Rosner, A. Leithe-Jasper, M. Baenitz, J.A. Mydosh, and Y. Grin — Max-Planck-Institut für Chemische Physik fester Stoffe, Dresden, Germany
Filled skutterudites adopt crystal structures with weakly bonded fillers M which can move in an oversized cavity. While the compounds NaFe4Sb12 and KFe4Sb12 are weak itinerant electron ferromagnets below ≈ 80 K [1,2], the isostructural alkaline-earth and the La and Yb-filled compounds are paramagnets down to 2 K. Specific heat measurements at low temperatures reveal electronic terms γ ranging from 100 to 200 mJ/mol K2, irrespective of the ground state. A field dependence of γ is only found for LaFe4Sb12. In addition, an Einstein term to cp(T) with ΘE between 70 K and 105 K is detected. Full potential band structure calculations for NaFe4Sb12 suggest an energetically driven off-center motion of the Na in its cage by about 0.1 Å. From temperature-dependent atomic displacement factors determined by X-ray diffraction the Einstein temperature and the heat capacity are calculated and compared with our structural data.
[1] A. Leithe-Jasper et al. Phys. Rev. Lett. 91, 037208 (2003).
[2] A. Leithe-Jasper et al. Phys. Rev. B, in print (1 Dec 2004).