Spin phonon interactions and magnetodielectric effects in multiferroic BiFeO₃–PbTiO₃

Here, we report the observation of magneto-dielectric and magneto-structural coupling in (1  −  x)BiFeO₃–xPbTiO₃ i.e.(1  −  x)BF–xPT) solid solutions with compositions in the vicinity of morphotropic phase boundary, as manifested by a combination of temperature dependent magnetic, Raman and dielectric measurements. Whilst x-ray diffraction and Raman spectroscopy suggest absence of any structural phase transition between 90–300 K, temperature dependent magnetic studies reveal magnetic anomalies in the solid solutions. These results are complemented by identical observations in the dielectric measurements at similar temperatures indicating a coupling between magnetic and electric order parameters. Further, Raman studies on rhombohedral i.e. x  =  0.20 samples reveal a coupling between the magnetic structure and the lattice, causing spin-phonon interactions that are possibly responsible for observed magneto-dielectric effects. Our results illustrate that the phase transitions in BiFeO₃–PbTiO₃ system are fewer than expected and are attributed to a spatial averaging in an inhomogeneous albeit single-phase material due to clustering of Fe- or Ti-ions on different length scales. (paper)