NMR and NQR study of the tetrahedral frustrated quantum spin system Cu2Te2O5Br2 in its paramagnetic phase

TL;DR

This study uses NMR and NQR techniques to investigate the magnetic properties and exchange interactions in the frustrated quantum spin system Cu2Te2O5Br2, revealing the roles of tellurium and bromine in its magnetic behavior.

Contribution

It provides new insights into the hyperfine interactions and the role of Te and Br in the exchange pathways of Cu2Te2O5Br2 using NMR and NQR measurements.

Findings

Identified a magnetic transition at 10.5K at 9T.

Ruled out one-dimensional divergence of spin-spin correlations.

Demonstrated the importance of tellurium and bromine in exchange interactions.

Abstract

The quantum antiferromagnet Cu2Te2O5Br2 was investigated by NMR and NQR. The 125Te NMR investigation showed that there is a magnetic transition around 10.5K at 9T, in agreement with previous studies. From the divergence of the spin-lattice relaxation rate, we ruled out the possibility that the transition could be governed by a one-dimensional divergence of the spin-spin correlation function. The observed anisotropy of the 125Te shift was shown to be due to a spin polarization of the 5s2 "E" doublet of the [TeO3E] tetrahedra, highlighting the importance of tellurium in the exchange paths. In the paramagnetic state, Br NQR and NMR measurements led to the determination of the Br hyperfine coupling and the electric field gradient tensor, and to the the spin polarization of Br p orbitals. The results demonstrate the crucial role of bromine in the interaction paths between Cu spins.