Ultrafast control of magnetic interactions by light driven phonons

Resonant ultrafast excitation of infrared-active phonons is a powerful technique to control the electronic properties of materials, leading to remarkable phenomena such as light-induced enhancement of superconductivity, switching of ferroelectric polarization and ultrafast insulator to metal transitions. Here we show that light-driven lattice vibrations can be utilized to coherently manipulate macroscopic magnetic states. Intense mid-infrared electric field pulses, tuned to resonance with a vibrational normal mode of the archetypical antiferromagnet DyFeO₃, induce ultrafast and long-living changes of the fundamental exchange interaction between rare-earth orbitals and transition metal spins. Non-thermal lattice control of the magnetic exchange, defining the very stability of the macroscopic magnetic state, allows us to perform a coherent switching between competing antiferromagnetic and weakly ferromagnetic spin orders on the fastest possible timescale. Our discovery outlines the broad potential of resonant lattice excitation for the manipulation of ferroic order on ultrafast timescales.