RESUMEN
We prepared trirutile-type polycrystalline samples of CuTa2O6 by low-temperature decomposition of a Cu-Ta-oxalate precursor. Diffraction studies at room temperature identified a slight monoclinic distortion of the hitherto surmised tetragonal trirutile crystal structure. Detailed high-temperature X-ray and neutron powder diffraction investigations as well as Raman scattering spectroscopy revealed a structural phase transition at 503(3) K from the monoclinic structure to the tetragonal trirutile structure. GGA+U density functional calculations of the spin-exchange parameters as well as magnetic susceptibility and isothermal magnetization measurements reveal that CuTa2O6 is a new 1D Heisenberg magnet with predominant anti-ferromagnetic nearest-neighbor intrachain spin-exchange interaction of â¼50 K. Interchain exchange is a factor of â¼5 smaller. Heat capacity and low-temperature high-intensity neutron powder diffraction studies could not detect long-range order down to 0.45 K.
RESUMEN
The new oxofluoride FeSeO3F, which is isostructural with FeTeO3F and GaTeO3F, was prepared by hydrothermal synthesis, and its structure was determined by X-ray diffraction. The magnetic properties of FeSeO3F were characterized by magnetic susceptibility and specific heat measurements, by evaluating its spin exchanges on the basis of density functional theory (DFT) calculations, and by performing a quantum Monte Carlo simulation of the magnetic susceptibility. FeSeO3F crystallizes in the monoclinic space group P21/n and has one unique Se(4+) ion and one unique Fe(3+) ion. The building blocks of FeSeO3F are [SeO3] trigonal pyramids and cis-[FeO4F2] distorted octahedra. The cis-[FeO4F2] octahedra are condensed by sharing the O-O and F-F edges alternatingly to form [FeO3F]∞ chains, which are interconnected via the [SeO3] pyramids by corner-sharing. The magnetic susceptibility of FeSeO3F is characterized by a broad maximum at 75(2) K and a long-range antiferromagnetic order below â¼45 K. The latter is observed by magnetic susceptibility and specific heat measurements. DFT calculations show that the Fe-F-Fe spin exchange is stronger than the Fe-O-Fe exchange, so each [FeO3F]∞ chain is a Heisenberg antiferromagnetic chain with alternating antiferromagnetic spin exchanges. The temperature dependence of the magnetic susceptibility is well-reproduced by a quantum-Monte Carlo simulation.