  Static strain in complex oxide heterostructures has been extensively used to
engineer electronic and magnetic properties at equilibrium. In the same spirit,
deformations of the crystal lattice with light may be used to achieve
functional control across hetero-interfaces dynamically. Here, by exciting
large amplitude infrared-active vibrations in a LaAlO3 substrate we induce
magnetic order melting in a NdNiO3 film across a hetero-interface. Femtosecond
Resonant Soft X-ray Diffraction is used to determine the spatial and temporal
evolution of the magnetic disordering. We observe a magnetic melt front that
grows from the substrate interface into the film, at a speed that suggests
electronically driven propagation. Light control and ultrafast phase front
propagation at hetero-interfaces may lead to new opportunities in
optomagnetism, for example by driving domain wall motion to transport
information across suitably designed devices.
