Raman scattering in orthorhombic multiferroic : The role of mixing of lowest harmonics among the components of magnetization

The local inversion symmetry breaking on the center of the Mn–O–Mn bond in the orthorhombically distorted MnO 6 octahedra in RMnO 3 gives rise to a distortion which produces local polarization and it averages out to 0 due to the symmetry of the ground state. This can be understood through a magnetoelectric coupling term in the free energy expansion which goes as ∼ P M 2 according to the Pbnm symmetry. The dynamical fluctuation of P → , which is nonzero, couples to the lowest harmonics of the components of M → yielding a double peak structure in the electromagnon spectrum. The recently observed Raman data in this material can successfully be explained through this scenario.