The magnetoelectric effect and double-perovskite structure.

Based on a microscopic model with a biquadratic magnetoelectric coupling the properties of Bi2NiMnO6 thin films are investigated. Using Green's functions the phonon spectrum is calculated which is determined by the polarization and the magnetization. The phonon energy and its damping offer a kink at the magnetic phase transition temperature. The phonon energy is enhanced if an external magnetic field is increased, whereas, the damping of the phonons decreases. The observed behavior is a strong evidence for a magnetoelectric coupling. The relevance of our approach for other multiferroics is discussed. [ABSTRACT FROM AUTHOR]