Optical excitation of electromagnons in hexaferrite

TL;DR

This paper demonstrates ultrafast control of magnetism in a room-temperature multiferroic hexaferrite via optical excitation, revealing a new mechanism involving spin-lattice coupling that induces coherent magnons and transient polarization changes.

Contribution

It introduces a novel microscopic mechanism based on spin-lattice coupling for triggering coherent magnons in ferrimagnetic insulators using femtosecond optical pulses.

Findings

Femtosecond above-bandgap excitation induces coherent magnons.

Magnetic sublattices entangle and modulate polarization transiently.

Proposes a new pathway for ultrafast magnetic control.

Abstract

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