Structure and magnetic properties of the ternary compound copper iron telluride

Initial measurements made by X-ray diffraction on polycrystalline samples indicated that stoichiometric CuFeTe2 did not show single phase behaviour, but that samples with composition Cu1.13Fe1.22Te2 (CFT) were single phase. Neutron diffraction measurements were made on a sample of CFT at Various temperatures in the range 4.2-300 K using a neutron wavelength of 0.15525 nm. Analysis of the resulting data showed that CFT has a defect Cu2Sb-type structure with space group P4/nmm and lattice parameters a = 0.39850 and c = 0.60920 nm at room temperature. It was shown that the 2a(0 0 0) sites are occupied by Cu and Fe and 2c(0 1/2 z) sites by Te, while the excess Cu and Fe occupy 2c'(0 1/2 z') sites, which are 10-15% filled. However, no ordering of the Cu and Fe on either type of site could be detected. Also, no extra magnetic lines were observed at any temperature, indicating that no ordered magnetic structure was observed. Measurements of magnetic susceptibility as a function of temperature on CFT samples showed the presence of a spin-glass transition in the range 60-80 K. The spin-glass behaviour is attributed to the effects of Fe atoms in the 2c' sites which cause frustration in the Fe atoms on the 2a sites, Any local variation of the density of 2c' Fe atoms would result in a corresponding variation of the spin-glass transition temperature, as observed. (C) 1998 Elsevier Science B.V. All rights reserved.