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Abstract:
Centimetre-sized single crystals of high-quality CaBaCo2Fe2O7 were
synthesized by the optical floating zone technique. The metal-to-metal
stoichiometry and oxygen content were confirmed by spectroscopy and
thermal reduction experiments. The hexagonal symmetry P6(3)mc (No. 186)
well describes the powder X-ray and neutron diffraction as well as
single-crystal neutron diffraction at all measured temperatures. This
symmetry is also consistent with optical second harmonic generation data
obtained between 10 and 295 K. However, a satisfactory structure
description from single-crystal neutron diffraction data needs an oxygen
split position. Specific heat, magnetic susceptibility and powder
neutron diffraction data indicate a magnetic phase transition at T-N =
159 K to an antiferromagnetic ground state, but with a persisting
hexagonal symmetry and intrinsic geometric frustration.
