Incommensurate magnetic ordering in $C{u}_{2}T{e}_2{O}_5{X}_2$ (X=Cl,Br) studied by neutron diffraction

Abstract

We present the results of the first neutron powder and single crystal diffraction studies of the coupled spin tetrahedra systems ${\CuTeX}$ (X=Cl, Br). Incommensurate antiferromagnetic order with the propagation vectors ${\bf{k}_{Cl}}\approx[0.150,0.422,\half]$, ${\bf{k}_{Br}}\approx[0.158,0.354,\half]$ sets in below $T_N$=18 K for X=Cl and 11 K for X=Br. No simple collinear antiferromagnetic or ferromagnetic arrangements of moments within Cu${}^{2+}$ tetrahedra fit these observations. Fitting the diffraction data to more complex but physically reasonable models with multiple helices leads to a moment of 0.67(1)${\mu }_B$/Cu${}^{2+}$ at 1.5 K for the Cl-compound. The reason for such a complex ground state may be geometrical frustration of the spins due to the intra- and inter-tetrahedral couplings having similar strengths. The magnetic moment in the Br- compound, calculated assuming it has the same magnetic structure as the Cl compound, is only 0.51(5)${\mu }_B$/Cu${}^{2+}$ at 1.5 K. In neither compound has any evidence for a structural transition accompanying the magnetic ordering been found.

References in corpus (8)

• Evidence for an unconventional magnetic instability in the spin-tetrahedra system Cu_2Te_2O_5Br_2
• Longitudinal magnon in the tetrahedral spin system Cu2Te2O5Br2 near quantum criticality
• Magnetism of a tetrahedral cluster spin-chain
• Halogen-mediated exchange in the coupled-tetrahedra quantum spin systems Cu2Te2O5X2 (X=Br,Cl)
• Spin dynamics of a tetrahedral cluster magnet
• Low-lying excitations and magnetization process of coupled tetrahedral systems
• Magnetic Raman scattering of the ordered tetrahedral spin-1/2 clusters in Cu_2Te_2O_5(Br_(1-x)Cl_x)_2 compounds
• Ground state order and spin-lattice coupling in tetrahedral spin systems Cu2Te2O5X2

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