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TT: Fachverband Tiefe Temperaturen

TT 25: Correlated Electrons: Quantum-Critical Phenomena 1

TT 25.10: Vortrag

Mittwoch, 28. März 2012, 12:00–12:15, H 3010

Electron Spin Resonance of the Yb 4f-moment in Yb(Rh_1−xCo_x)₂Si₂ — Thomas Gruner, •Jörg Sichelschmidt, Christoph Klingner, Cornelius Krellner, Christoph Geibel, and Frank Steglich — Max Planck Institute for Chemical Physics of Solids, 01187 Dresden

The evolution of spin dynamics from the quantum critical system YbRh₂Si₂ to the stable trivalent Yb system YbCo₂Si₂ was investigated by Electron Spin Resonance (ESR) spectroscopy. While the Kondo temperature changes by one order of magnitude all compositions of the single crystalline series Yb(Rh_1−xCo_x)₂Si₂ show well defined ESR spectra with a clear Yb³⁺ character for temperatures below ≈ 20 K. With increasing Co-content the ESR g-factor along the c-direction strongly increases indicating a continuous change of the ground state wave function and, thus, a continuous change of the crystal electric field. The linewidth presents a complex dependence on the Co-content and is discussed in terms of the Co-doping dependence of the Kondo interaction, of the magnetic anisotropy and the influence of ferromagnetic correlations between the 4f states. The results provide evidence that for low Co-doping the Kondo interaction allows narrow ESR spectra despite the presence of a large magnetic anisotropy whereas at high Co-concentrations the linewidth is controlled by ferromagnetic correlations. A pronounced broadening due to critical correlations at low temperatures is only observed at the highest Co-content. This might be related to the presence of incommensurate magnetic fluctuations.