Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 6: Correlated Electrons: Heavy Fermions

TT 6.8: Talk

Monday, February 25, 2008, 11:30–11:45, EB 202

The new Heavy Fermion System CeFePO: A ³¹P NMR study — •Eva Maria Brüning, Michael Baenitz, Cornelius Krellner, Christoph Geibel, and Frank Steglich — Max-Planck-Institut für Chemische Physik fester Stoffe

Among the CeTPO system (T = Ru, Os, Co, Fe), CeFePO is particular interesting because it presents Heavy Fermion behavior. Specific heat measurements above 400 mK clearly show the absence of magnetic order and a strongly enhanced Sommerfeld ratio γ = 700 mJ/molK², comparable to CeCu₂Si₂. ³¹P NMR field sweep measurements were performed at different fields (4.4 T and 1.5 T) and temperatures (2 K to 300 K). ³¹P Knight shift ³¹K(T) shows a field independent Curie-Weiss like behavior above 100 K consistent with χ(T) measurements, whereas towards lower temperatures a saturation occurred due to Kondo interaction. ³¹K(T) vs. χ(T) gives a hyperfine coupling constant of A_hf = 2 kOe/µ_B. ³¹(1/T₁) measurements were carried out at different fields (4.4 T and 1.5 T). ³¹(1/T₁T)(T) is field independent and shows a strong increase towards lower temperatures and a saturation towards an enhanced Korringa value for T→ 0, indicating a large N(E_F) value. ³¹(1/T₁T) is qualitatively similar to the ²⁹Si NMR results on CeCu₂Si₂ (7 T). Using ³¹P as a local probe, our ³¹P NMR results strongly confirm the Heavy Fermion scenario for this new compound.