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

Detailed Pt-195 and Yb-171 nuclear magnetic resonance (NMR) studies on the heterogeneous mixed valence system YbPtGe2 are reported. The temperature dependence of the Pt-195-NMR shift K-195(T) indicates the opening of an unusual magnetic gap below 200 K. K-195(T) was analyzed by a thermal activation model which yields an isotropic gap Delta/k(B) approximate to 200 K. In contrast, the spin-lattice relaxation rate (195)(1/T-1) 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/T-1) follows a simple metallic behavior, similar to the reference compound YPtGe2. A well-resolved NMR line with small shift is assigned to divalent Yb-171. 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.