Incommensurate magnetic ordering in Cu{sub 2}Te{sub 2}O{sub 5}X{sub 2} (X=Cl,Br) studied by single crystal neutron diffraction
Polarized and unpolarized neutron-diffraction studies have been carried out on single crystals of the coupled spin tetrahedra systems Cu{sub 2}Te{sub 2}O{sub 5}X{sub 2} (X=Cl,Br). A model of the magnetic structure associated with the propagation vectors k{sup '}{sub Cl}{approx_equal}(-0.150,0.422,(1/2)) and k{sup '}{sub Br}{approx_equal}(-0.172,0.356,(1/2)) and stable below T{sub N}=18 K for X=Cl and T{sub N}=11 K for X=Br is proposed. A feature of the model, common to both the bromide and chloride, is a canted coplanar motif for the four Cu{sup 2+} spins on each tetrahedron which rotates on a helix from cell to cell following the propagation vector. The Cu{sup 2+}more »