Two-Magnon Raman Scattering in Strontium Orthoferrites

Raman spectra have been measured in polycrystalline samples of La 0.5 Sr 0.5 FeO 3–δ and SrFeO 2.5 antiferromagnetic orthoferrites in the orthorhombic and brownmillerite phases, respectively, in the temperature range of 300–700 K. A significant decrease in the intensity of the 1300–1400 cm –1 band when approaching the Néel temperature ( T N ~ 410 K in the substituted orthoferrite La 0.5 Sr 0.5 FeO 3–δ and T N ~ 670 K in the brownmillerite SrFeO 2.5 ) indicates magnetic ordering in the crystals under normal conditions, and the band itself is due to two-magnon scattering, in contrast to the ~1100-cm –1 biphonon scattering band, which retains its intensity over the entire temperature range.