NMR and NQR study of the tetrahedral frustrated quantum spin systemCu2Te2O5Br2in its paramagnetic

Abstract

The quantum antiferromagnet Cu2Te2O5Br2 was investigated by NMR and NQR. The 125 Te NMR investigation showed that there is a magnetic transition around 10.5 K at 9 T, 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 125 Te shift was shown to be due to a spin polarization of the 5s 2 "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.

Persistence of singlet fluctuations in the coupled spin tetrahedra system Cu2Te2O5BrBaek1, Choi2, Berger3 et al. 2012Phys. Rev. B

“…The extremely narrow transition width (≪ T 0 ) above T 0 corroborates the 3D character of the magnetic order suggested in previous studies. 17,20,21 Surprisingly, T 0 identified in our study is considerably higher than 11.4 K in Ref. 9 and 10.5 K in Ref.…”

“…9 and 10.5 K in Ref. 17. While a higher T 0 usually suggests a higher sample quality, the strongly sample-dependent variation of T 0 up to 30% is quite unusual.…”

Magnetic resonance as a local probe for kagomé magnetism in Barlowite Cu4(OH)6FBr

“…Two I = 3 2 -isotopes with 100% natural abundance in total and relatively large quadrupole moments on both nuclei identifies Br-NMR and NQR as a powerful technique which is frequently applied on quantum spin systems and other forms of matter. [22][23][24][25] Our Br magnetic resonance study presented here aims for the consistent determination of the quadrupole coupling constant ν Q and the asymmetry parameter η from NMR and NQR. Figure 2 shows the field sweep 1 H-and 19 F-NMR spectra measured at a fixed frequency of 84.44 MHz for different temperatures.…”

Frustrated Antiferromagnetic Spin Chains of Edge-Sharing Tetrahedra in Volcanic Minerals K3Cu3(Fe0.82Al0.18)O2(SO4)4 and K4Cu4O2(SO4)4MeCl

“…We did not manage to find in the literature any data on experimental studies of magnetic compounds, in which spin tetrahedra would be linked into chains via edges. Instead of the tetrahedral-cluster spin chain and the spin chain of edge-sharing tetrahedra, the system Cu2Te2O5X2 with X -Cl, Br has been examined in the literature [36,37,56,57] . It contains tetrahedral clusters of copper ions (Cu4), which are not edgesharing, but align to tubes or chains.…”

“…However, in spite of numerous theoretical and experimental studies, the accurate dimensionality of the Cu2Te2O5X2 system is not clear. There exists the opinion that this system is three-dimensional rather than quasi-one dimensional, since interchain interactions in it are rather strong1 [7,37,56,57]. Different models of the magnetic state of this system were examined in theoretical terms.…”