Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
MA: Magnetismus
MA 4: Kondo / Schwer-Fermionen / Quasi-Niedrigdimensionale Systeme (gemeinsam mit TT)
MA 4.9: Vortrag
Montag, 24. März 2003, 12:15–12:30, HSZ/405
Optical investigations of the band structure of α −Eu8Ga16Ge30 — •J. Sichelschmidt1, V. Voevodin1, S. Kimura2, V. Pacheco1, A. Bentien1, S. Paschen1, Y. Grin1, and F. Steglich1 — 1Max-Planck-Institut für Chemische Physik fester Stoffe, D-01187 Dresden, Germany — 2UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
The clathrate compound Eu8Ga16Ge30 is made up of large cages of Ge and Ga. The interior of these cages is fully occupied by Eu2+ ions which make this clathrate a local moment ferromagnet. The recently discovered α-modification shows a very low Curie temperature of TC=10.5 K [1] and therefore is particularly interesting for the search of new kinds of Kondo-Insulators [2].
We performed measurements of the optical reflectivity of α −Eu8Ga16Ge30 in the energy range 5 meV - 30 eV in order to characterize the band structure of this system. The low energy Drude type of reflectivity is characterized by a very low charge carrier density in accordance with the results of Hall measurements which showed charge carrier densities as low as 0.16 electrons per formular unit. A low energy peak at around 0.2 eV is splitted below TC where ferromagnetic ordering sets in. This peak is attributed to an interband transition between Eu 4f7 and Eu 5d1 states. The onset for other interband transition occurs at energies of approximately 0.5 eV.
[1] S. Paschen et al., Phys. Rev. B 64, 214404 (2001)
[2] G. Aeppli and Z. Fisk, Comments Cond. Mat. Phys. 16, 155 (1992)