BiFeO₃ is a unique material that exhibits ferroelectric and weak ferromagnetic (or canted anti-ferromagnetic) orderings simultaneously far above room temperature (Curie temperature T_C ~1100K and Néel temperature T_N ~640K). This property, called multiferroics, results in a coupling between electric field and magnetization; the so-called electromagnetic effect. Because of this attractive nature, BiFeO₃ now gathers great attention as a prominent candidate for future innovative electronc devices such as energy-saving memories and transisters. For device applications, however, further investigations for its basic physics both in electric and magnetic properties are strongly expected. For example, as a recent hot topic, BiFeO₃ thin films greatly increased their remanent electric polarization by doping with Mn, though the mechanism has been left an open question.[1]

    To solve this problem, we synthesized here Mn-doped BiFeO₃ samples by a sol-gel process with molar compositions of [Mn]=0-10%, and investigated their lattice properties by Raman scattering, x-ray diffraction and transmission electron microscopy. Our results showed that the samples included no seconadary phases and the Mn ions substituted Fe sites of host lattice. Small lattice distortion from the rhombohedral structure of BiFeO₃ was observed with increasing [Mn]. Moreover, phonon Raman spectra observed at 300-800K showed anomalous behavior near T_N. This was interpreted by a coupling between the phonon and spin systems.

[1] S. K. Singh, H. Ishiwara and K. Maruyama , Appl. Phys. Lett. 88 26908 (2006)

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1. Micro-Raman study of BiFeO₃ thin films fabricated by chemical solution deposition using different Bi/Fe ratio precursors