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TT: Fachverband Tiefe Temperaturen

TT 26: CE: Heavy Fermions

TT 26.11: Vortrag

Mittwoch, 24. März 2010, 16:45–17:00, H21

Study of the temperature dependence of the magnetic excitations in CeCu₂Ge₂ — •Astrid Schneidewind¹, Oliver Stockert², Karin Schmalzl³, Enrico Faulhaber¹, Micha Deppe², and Michael Loewenhaupt⁴ — ¹Joint Research Group Helmholtz-Zentrum Berlin - Technische Universität Dresden, Garching, Germany — ²Max-Planck-Institut für Chemische Physik fester Stoffe, Dresden, Germany — ³Jülich Centre for Neutron Science at Institut Laue-Langevin, Grenoble, France — ⁴Institut für Festkörperphysik, Technische Universität Dresden, Dresden, Germany

Long-range antiferromagnetic order establishes in the heavy fermion compound CeCu₂Ge₂ below T_N = 4.15 K with an amplitude modulated structure and an ordering wave vector Q_AF = (0.28 0.28 0.543) [1]. Due to the Kondo effect the ordered moment is slightly reduced to m ≈ 1.0 µ_B at low temperatures [1].

We performed inelastic neutron scattering on a CeCu₂Ge₂ single crystal to study the low energy magnetic excitations in the ordered state. At lowest temperatures, dispersive spin waves have clearly been observed. At the magnetic zone centre the spin waves are gapped with Δ E ≈ 0.55 meV. The excitation spectrum changes with increasing temperatures and the gap closes giving rise to quasielastic scattering just below T_N. The distinct behaviour of the magnetic excitation spectra can be related to the different magnetically ordered phases in CeCu₂Ge₂.

[1] A. Krimmel et al., Phys. Rev. B 55 (1997) 6416.