Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 8: Correlated Electrons: Heavy Fermions
TT 8.12: Vortrag
Montag, 27. März 2006, 17:30–17:45, HSZ 301
Crossover from divalent to valence fluctuating state of Eu in EuCu2(Ge1−xSix)2 probed by 63,65Cu-NMR — •M. Baenitz1, Eva Brüning1, Andrei Gippius2, Anakan Rajarajan1, Elena Morozova2, Zakir Hossain3, Christoph Geibel1, and Frank Steglich1 — 1Max Planck Institute for Chemical Physics of Solids, Dresden, Germany — 2Moscow State University, Moscow, Russia — 3Department of Physics, Indian Institute of Technology, Kanpur, India
Temperature dependent 63,65Cu field sweep NMR investigations on a series of EuCu2(Ge1−xSix)2 powder samples (x = 0, 0.3, 0.65, 0.7, 1) are presented. EuCu2 (Ge, Si)2 is unique among Eu-intermetallics because, upon tuning from a divalent antiferromagnetically ordered state for x = 0 to a valence fluctuating state for x = 1, Heavy Fermion behaviour was found around x ≈ 0.7. The Knight shift 63,65K is negative for all stoichiometries. Hyperfine fields are largest for the antiferromagnetically ordered Ge-rich compounds, and smallest for the valence fluctuating pure silicon compound (x = 1). For the x = 0.3 compound, above TN ≈ 19 K,63K(T) exhibits a Curie-Weiss like behaviour (≈ −10 % at 20 K) whereas for EuCu2Si2 a temperature independent shift of 63K(T)≈ −1.5 % is found. Our results are discussed in terms of formation of heavy quasiparticles and/or presence of valence fluctuations of Eu.