Spin gap behavior in Cu$_2$Sc$_2$Ge$_4$O$_{13}$ by $^{45}$Sc nuclear magnetic resonance

TL;DR

This study uses $^{45}$Sc NMR to investigate the spin gap in Cu$_2$Sc$_2$Ge$_4$O$_{13}$, confirming low-dimensional magnetism and quantifying a spin gap of about 275 K consistent with neutron scattering data.

Contribution

The paper provides the first NMR evidence of a spin gap in Cu$_2$Sc$_2$Ge$_4$O$_{13}$ and demonstrates that a spin dimer model accurately describes its magnetic behavior.

Findings

NMR shift shows a broad maximum at ~170 K.

Activated responses indicate a spin gap of about 275 K.

Data fits well with the spin dimer model.

Abstract

We report the results of a $^{45}$Sc nuclear magnetic resonance (NMR) study on the quasi-one-dimensional compound Cu$_2$Sc$_2$Ge$_4$O$_{13}$ at temperatures between 4 and 300 K. This material has been a subject of current interest due to indications of spin gap behavior. The temperature-dependent NMR shift exhibits a character of low-dimensional magnetism with a negative broad maximum at $T_{max}$ $\simeq $ 170 K. Below $% T_{max}$, the NMR shifts and spin lattice relaxation rates clearly indicate activated responses, confirming the existence of a spin gap in Cu$_2$Sc$_2$Ge% $_4$O$_{13}$. The experimental NMR data can be well fitted to the spin dimer model, yielding a spin gap value of about 275 K which is close to the 25 meV peak found in the inelastic neutron scattering measurement. A detailed analysis further points out that the nearly isolated dimer picture is proper for the understanding of spin gap nature in Cu$_2$Sc$_2$Ge$_4$O$_{13}$.