  Exciting atomic oscillations with light is a powerful technique to control
the electronic properties of materials, leading to remarkable phenomena such as
light-induced superconductivity and ultrafast insulator to metal transitions.
Here we show that light-driven lattice vibrations can be utilised to encode
efficiently spin information in a magnetic medium. Intense mid-infrared
electric field pulses, tuned to resonance with a vibrational normal mode of
antiferromagnetic DyFeO3, drive the emergence of long-living weak ferromagnetic
order. Light-driven phonon displacements promptly lower the energy barrier
separating competing magnetic states, allowing the alignment of spins to occur
within a few picoseconds, via non-equilibrium dynamics of the magnetic energy
landscape.
