Dresden 2011 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 56: CE: Heavy Fermions
TT 56.9: Talk
Thursday, March 17, 2011, 18:45–19:00, HSZ 105
Spin dynamics in EuCu2Si2−xGex : from mixed valence to magnetic instability — •Kirill Nemkovski1, Pavel Alekseev2, Jean-Michel Mignot3, Ross Stewart4, Robert Bewley4, and Alexandr Gribanov5 — 1Jülich Centre for Neutron Science, Forschungszentrum Jülich, Germany — 2RRC "Kurchatov Institute", Moscow, Russia — 3Laboratoire Léon Brillouin, CEA/Saclay, France — 4ISIS, Rutherford Appleton Laboratory, Didcot, UK — 5Department of Chemistry, Moscow State University, Russia
EuCu2Si2−xGex series represents the only known case among Eu- and Sm-based systems, where the state in the phase diagram is tuned from the valence-fluctuating one to heavy-fermion, and then to magnetic-ordered state, with quantum critical point near x=0.7. Here we present the inelastic neutron scattering study of spin dynamics in EuCu2Si2−xGex (x=0, 0.2, 0.5, 0.8), performed in a wide temperature range (5-200K). At x=0 the magnetic excitation spectrum was found to be represented by the double-peak structure just below the energy range of the Eu3+ spin-orbit (SO) excitation 7F0→7F1, so that at least the high-energy spectral component can be assigned to the renormalized SO transition. Change of the Eu valence towards 2+ with increase of the temperature and/or Ge concentration results in further renormalization (lowering the energy) and gradual suppression of both inelastic peaks in the spectrum, along with developing sizeable quasielastic signal. The origin of the spectral structure and its evolution is discussed in terms of excitonic model for the mixed-valence state. This work was supported by RFBR grant No. 11-02-00121.