Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 3: Correlated Electrons: Heavy Fermions
TT 3.8: Vortrag
Montag, 26. März 2012, 11:30–11:45, H 3005
Ferromagnetic correlations in Yb based heavy fermions probed by NMR relaxation: YbNi4P2 vs. Yb(Rh,Ir)2Si2 — •M. Baenitz, R. Sarkar, P. Khuntia, C. Krellner, C. Geibel, and F. Steglich — Max - Planck Institute of Chemical Physics of Solids, 01187 Dresden, Germany.
Intersite correlations in Ce-based heavy fermion systems close to the quantum critical point separating the magnetic ordered state from the paramagnetic Kondo lattice are in almost all cases predominantly antiferromagnetic (AFM) in nature. The NMR relaxation of these systems show an evolution from localized fluctuations with 1/T1 nearly constant above the Kondo temperature TK, to a linear in T Korringa- like behavior with a constant and enhanced (1/T1T)- value below TK. We report on 31P-NMR results on the ferromagnetic (FM) quantum critical system YbNi4P2 over a wide range in temperature (2-300 K) and field (0.2 - 9 T). Here, 31(1/T1T)(T) does not show such a signature at TK, instead a continuous increase of (1/T1T) down to lowest T is observed. A similar behavior has been reported for YbRh2Si2, which also exhibits strong FM correlations evidenced by 29Si - NMR and an enhanced Wilson ratio. Furthermore, in CeFePO, which is likely unique among Ce-based quantum critical system because of its strong FM correlations, (1/T1T) also diverges continuously for T—→ 0. This suggests that the difference in the relaxation between most of the Ce systems and the Yb systems is predominantly related to a change from AFM to FM intersite correlations. NMR-results (shift, line width, T1) are analyzed and discussed in diffrent models (Korringa, Moriya).