Unconventional magnetism in multivalent charge-ordered YbPtGe${}_2$ probed by ${}^{195}$Pt- and ${}^{171}$Yb-NMR

Abstract

Detailed ${}^{195}$Pt- and ${}^{171}$Yb nuclear magnetic resonance (NMR) studies on the heterogeneous mixed valence system YbPtGe${}_2$ are reported. The temperature dependence of the ${}^{195}$Pt-NMR shift ${}^{195}K(T)$ indicates the opening of an unusual magnetic gap below 200\,K. ${}^{195}K(T)$ was analyzed by a thermal activation model which yields an isotropic gap $\hat{I}”/k_B\approx 200$\,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 YPtGe${}_2$. A well resolved NMR line with small shift is assigned to divalent ${}^{171}$Yb. This finding supports the proposed model with two sub-sets of Yb species (di- and trivalent) located on the Yb2 and Yb1 site of the YbPtGe${}_2$ lattice.

Submitted in Physical Review B (Rapid Communication)