Optical excitation of electromagnons in hexaferrite

Understanding ultrafast magnetization dynamics on the microscopic level is of strong current interest due to potential for applications in information storage. In recent years, spin-lattice coupling has been recognized as essential dynamics. Magnetoelectric multiferroics type II possess intrinsic correlations among magnetic sublattices and electric polarization $(P)$ through coupling, enabling fundamentally coupled between spins lattice. Here, we report a room-temperature multiferroic hexaferrite possessing ferrimagnetic (FM) antiferromagnetic sublattices, revealed by time-resolved resonant x-ray diffraction. A femtosecond above-bandgap excitation triggers coherent magnon which two entangle give rise transient modulation $P$. mechanism triggering this FM insulator based proposed. Our finding opens general pathway control magnetism.