Phonon and magnetic dimer excitations in Fe-based S = 2 spin-ladder compound BaFe2Se2O

Raman scattering spectra of the new Fe-based S = 2 spin-ladder compound BaFe2Se2O are measured in a temperature range between 15 and 623 K. All six A(1g) and two B-1g Raman active modes of BaFe2Se2O, predicted by the factor-group analysis, have been experimentally observed at energies that are in a rather good agreement with the lattice dynamics calculation. The antiferromagnetic long-range spin ordering in BaFe2Se2O below T-N = 240 K leaves a fingerprint both in the A(1g) and B-1g phonon mode linewidth and energy. In the energy range between 400 and 650 cm(-1) we have observed a magnetic excitation related structure in the form of a magnon continuum, with the peaks corresponding to the singularities in the one-dimensional density of magnon states. The onset value of magnetic continuum (2 Delta(S)) is found at about 437 cm(-1) at 15 K. The magnetic continuum disappears at about 623 K, which led us to conclude that the short-range magnetic ordering in BaFe2Se2O exists apparently up to 2.6T(N).