Prediction of electromagnons in antiferromagnetic ferroelectrics from first-principles: The case of BiFeO3

A first-principles-based computational approach is developed to study finite-temperature complex dynamics in multiferroics. Application of the technique to one of the most well-known multiferroic, BiFeO3, predicts the existence of electromagnons that have so far remained elusive for first-principles computations. It is demonstrated that the most general form of the magnetoelectric coupling that is allowed in any multiferroic, may produce an electromagnon in antiferromagnetic ferroelectric. This finding could be explained from the basic theory of antiferromagnetic resonance. The temperature evolution of the electromagnon, magnon and soft phonon modes is studied to trace the intrinsic features of these excitations. A connection with experiment is also made.