Phonon Anomalies And Magnetic Excitations In Bafe2se2o

We report a temperature- and magnetic-field-dependent Raman-scattering study of the spin-ladder compound BaFe2Se2O. Temperature evolution of the B-1g mode self-energies revealed anomalous behavior at about 100 and 240 K with strong temperature-dependent Fano asymmetry. Furthermore, the A(g) modes integrated intensity exhibits an additional change in tendency at about 50 K. All the observed anomalies can be traced back to spin-phonon interaction contributions as well as multiple magnetic phase transitions present in BaFe2Se2O also detected in the Raman continuum induced by the spin fluctuations. Moreover, the absence of magnetic-field dependence of the magnetic mode observed at 436 cm(-1) and the small linewidth and high intensity are different from the magnetic modes at about 650 cm(-1). This suggests a two-magnon continuum and a two-magnon bound state resonance for this mode.