Mechanism Of Field Induced Fermi Liquid State In Yb-Based Heavy-Fermion Compound: X-Ray Absorption Spectroscopy And Nuclear Magnetic Resonance Studies Of Ybco2zn20

We have investigated the field dependences of Yb valence as well as of the magnetic properties of the heavy-fermion (HF) compound YbCo2Zn20 by X-ray absorption spectroscopy, Co-59 nuclear magnetic resonance, and magnetization measurements. Our results clearly show that the mechanism of field-induced Fermi-liquid-like behavior does not involve variation in the Yb electronic configuration, and is of magnetic origin. Typical examples of the susceptibility for several Yb-based HF materials are presented, in which one can see systematic changes between localized and delocalized pictures of 4f electrons.