New magnetic phase transitions in BiFeO₃

Abstract

We observed Raman scattering from magnons in the frequency range from \n10 to 65 cm[?]1 in BiFeO3 single crystals at cryogenic temperatures; \nthe temperature dependence of the magnon frequency at 18.2 cm[?]1 \napproximates an S = 5/2 Brillouin function up to the temperature \n([?]280 K) at which the magnon becomes overdamped. The diverging cross \nsection and the frequency shift at [?]140 and [?]200 K implies a \nspin-reorientation transition as in orthoferrites.