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Zusammenfassung:
We present magnetization, specific heat, and Al-27 NMR investigations on
YbFe2Al10 over a wide range in temperature and magnetic field. The
magnetic susceptibility at low temperatures is strongly enhanced at weak
magnetic fields, accompanied by a ln (T-0/T) divergence of the low-T
specific heat coefficient in zero field, which indicates a ground state
of correlated electrons. From our hard-x-ray photoemission spectroscopy
study, the Yb valence at 50 K is evaluated to be 2.38. The system
displays valence fluctuating behavior in the low to intermediate
temperature range, whereas above 400 K, Yb3+ carries a full and stable
moment, and Fe carries a moment of about 3.1(mu B). The enhanced value
of the Sommerfeld-Wilson ratio and the dynamic scaling of the
spin-lattice relaxation rate divided by T[(27)(1/T1T)] with static
susceptibility suggests admixed ferromagnetic correlations. (27)(1/T1T)
simultaneously tracks the valence fluctuations from the 4f Yb ions in
the high temperature range and field dependent antiferromagnetic
correlations among partially Kondo screened Fe 3d moments at low
temperature; the latter evolve out of an Yb 4f admixed conduction band.
