Berlin 2005 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique
TT 16.19: Poster
Samstag, 5. März 2005, 11:00–16:30, Poster TU C
Tetracritical point in CeCu2(Si1−xGex)2 investigated by neutron diffraction — •Enrico Faulhaber1, Oliver Stockert2, Beatrice Grenier3, Bachir Ouladdiaf3, Micha Deppe2, Christoph Geibel2, Frank Steglich2, and Michael Loewenhaupt1 — 1Institut für Festkörperphysik, TU Dresden, D-01062 Dresden, Germany — 2Max-Planck-Institut für Chem. Physik fester Stoffe, D-01187 Dresden, Germany — 3Institut Laue-Langevin, F-38042 Grenoble, France
The heavy-fermion system CeCu2(Si1−xGex)2 attracts not only interest close to x = 0 with the interplay of antiferromagnetism and superconductivity in pure CeCu2Si2, but also in the vicinity of x = 0.25 where the antiferromagnetic order is suggested to change from a spin-density wave to a more localized type of magnetic order. Moreover, specific heat as well as thermal expansion measurements indicate the possible existence of a tetracritical point at x ≈ 0.25. For higher and lower Ge concentrations exists a first order transition below the Néel temperature, whereas for x = 0.25 both transitions seem to be degenerate. Furthermore, the anomalies in the thermal expansion have opposite signs below and above x = 0.25 suggesting a different magnetic stucture. We performed extensive neutron diffraction on CeCu2(Si1−xGex)2 single crystals with x = 0.16 and 0.45, i.e. on either site of x = 0.25. Both samples show antiferromagnetic order with slightly different propagation vectors followed by a lock-in transition. This suggests a modified nesting of the Fermi surface. The magnetic structure will be discussed in comparison to macroscopic measurements.