Regensburg 2002 – wissenschaftliches Programm

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MA: Magnetismus

MA 14: Schwere Fermionen, Kondo-Systeme II (gemeinsam mit TT)

MA 14.3: Vortrag

Donnerstag, 14. März 2002, 15:00–15:15, H20

YbFe2Ge2: Heavy Fermion with anomalous magnetic properties — •J. Ferstl, J. Custers, C. Geibel, and F. Steglich — Max Planck Institute for the Chemical Physics of Solids Noethnitzer Str. 40 01187 Dresden, Germany

In comparison with Ce-based compounds, only a few Yb-based Heavy Fermions were discovered in the past twenty years. Very little is known e.g. about Yb-compounds with Ge and a transition metal from the Fe- or Co-columns. Therefore we have first grown polycrystalline samples and then single crystals of YbFe2Ge2 and started a detailed investigation of its physical properties. We shall present preliminary results of resistivity, susceptibility and specific heat measurements. Intermediate-valent Yb-state with a low characteristic energy is indicated by the comparatively large value of the linear term in the low temperature specific heat, γ≈200mJ/molK2, and the temperature, T≈16K, of the maximum in the susceptibility measurement. The anomalous behavior of χ(T) can be fitted at high temperatures (T>100K) with a Curie-Weiss law with an effective moment of µeff=6.5µB, much larger than the value expected for Yb3+, and a very large Curie-Weiss temperature (θ=300K), while below T=300K the susceptibility increases more strongly with decreasing temperature, giving a reduced µeff and a smaller Curie-Weiss temperature. The well-defined maximum around 16K is the lowest among all intermediate-valent Yb-systems. These results will be discussed in comparison with related RT2X2 compounds and their magnetic properties. We suggest that the anomalous behavior of the susceptibility in YbFe2Ge2 is due to fluctuating Fe-moments.

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