Study of Phase Transitions and Magnetoelectric Coupling of Laser Ablated BiFeO3 Thin Films by Raman Scattering

Multiferroic epitaxial thin films of BiFeO₃ were grown on (100) SrTiO₃ substrates by pulsed laser deposition (PLD). The X-ray diffraction analysis shows that the films are highly c-axis oriented with high degree of crystallinity. The polarized Raman scattering shows the monoclinic structure of thin films at room temperature in contrary to the rhombohedral structure in the bulk and tetragonal and rhombohedral structure in the c-axis oriented thin films as reported earlier. The temperature variation (up to 1000degC) of Raman scattering reveals spin-phonon coupling around 370degC, the magnetic Neel temperature (T_N). The disappearance of stronger Raman modes revealed the structural (ferroelectric to paraelectric) phase transition at around 820degC temperature (T_c). The observation of no softening of phonon modes indicates nonoconventional ferroelectric. We observed an intermediate phase between 820-950degC before the transition to a high-temperature cubic phase.