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

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.

8 pages, 11 figures

References in corpus (9)

• Longitudinal magnon in the tetrahedral spin system Cu2Te2O5Br2 near quantum criticality
• Halogen-mediated exchange in the coupled-tetrahedra quantum spin systems Cu2Te2O5X2 (X=Br,Cl)
• Incommensurate magnetic ordering in $C{u}_{2}T{e}_2{O}_5{X}_2$ (X=Cl,Br) studied by neutron diffraction
• Spin dynamics of a tetrahedral cluster magnet
• Low-lying excitations and magnetization process of coupled tetrahedral systems
• Incommensurate magnetic ordering in Cu2Te2O5X2 (X=Cl, Br) studied by single crystal neutron diffraction
• Magnetic Raman scattering of the ordered tetrahedral spin-1/2 clusters in Cu_2Te_2O_5(Br_(1-x)Cl_x)_2 compounds
• Weak antiferromagnetism and dimer order in quantum systems of coupled tetrahedra
• Ground state order and spin-lattice coupling in tetrahedral spin systems Cu2Te2O5X2

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• Persistence of singlet fluctuations in the coupled spin tetrahedra system Cu2Te2O5Br2 revealed by high-field magnetization and 79Br NQR - 125Te NMR
• Frustrated antiferromagnetic spin chains of edge-sharing tetrahedra in volcanic minerals K3Cu3(Fe0.82Al0.18)O2(SO4)4 and K4Cu4O2(SO4)4MeCl