Unconventional magnetism in multivalent charge-ordered YbPtGe2 probed by 195Pt- and 171Yb-NMR.

Detailed 195Pt and 171Yb nuclear magnetic resonance (NMR) studies on the heterogeneous mixed valence system YbPtGe2 are reported. The temperature dependence of the 195Pt-NMR shift 195K(T) indicates the opening of an unusual magnetic gap below 200 K. 195K(T) was analyzed by a thermal activation model which yields an isotropic gap Δ/kB ≈ 200 K. In contrast, the spin-lattice relaxation rate 195(1/T1) does not provide evidence for the gap. Therefore, an intermediate-valence picture is proposed while a Kondo-insulator scenario can be excluded. Moreover, 195(1/T1) follows a simple metallic behavior, similar to the reference compound YPtGe2. A well-resolved NMR line with small shift is assigned to divalent 171Yb. This finding supports the proposed model with two subsets of Yb species (di- and trivalent) located on the Yb2 and Yb1 site of the YbPtGe2 lattice. [ABSTRACT FROM AUTHOR]