Spin-phonon interactions of multiferroic Bi₄Ti₃O ₁₂-BiFeO₃ ceramics: Low-temperature Raman scattering and infrared reflectance spectra investigations

Optical phonons of multiferroic Bi₄Ti₃O ₁₂-BiFeO₃ ceramic have been investigated by low temperature Raman scattering and infrared reflectance spectra. Anomalies at about 85 K can be observed from the temperature dependence of the Raman and infrared modes, which arise from spin-phonon interaction during antiferromagnetic to paramagnetic phase transition. It was found that the change of exchange interaction in magnetic phase transition can be induced by Fe-O-Fe octahedral tilting driven from the A-site atoms. Moreover, ferroelectricity- related displacement of Bismuth atoms suggests the coupling of magnetic and ferroelectric orders.