Title: Insight into the temperature dependent properties of the ferromagnetic Kondo lattice YbNiSn,
Abstract: Analyzing temperature dependent photoemission (PE) data of the ferromagnetic
Kondo-lattice (KL) system YbNiSn in the light of the Periodic Anderson model
(PAM) we show that the KL behavior is not limited to temperatures below a
temperature T_K, defined empirically from resistivity and specificic heat
measurements. As characteristic for weakly hybridized Ce and Yb systems, the PE
spectra reveal a 4f-derived Fermi level peak, which reflects contributions from
the Kondo resonance and its crystal electric field (CEF) satellites. In YbNiSn
this peak has an unusual temperature dependence: With decreasing temperature a
steady linear increase of intensity is observed which extends over a large
interval ranging from 100 K down to 1 K without showing any peculiarities in
the region of T_K ~ TC= 5.6 K. In the light of the single-impurity Anderson
model (SIAM) this intensity variation reflects a linear increase of 4f
occupancy with decreasing temperature, indicating an onset of Kondo screening
at temperatures above 100 K. Within the PAM this phenomenon could be described
by a non-Fermi liquid like T- linear damping of the self-energy which accounts
phenomenologically for the feedback from the closely spaced CEF-states.