Sub-picosecond magnetisation manipulation via femtosecond optical pumping has attracted
wide attention ever since its original discovery in 1996. However, the spatial evolution of the
magnetisation is not yet well understood, in part due to the difficulty in experimentally
probing such rapid dynamics. Here, we find evidence of a universal rapid magnetic order
recovery in ferrimagnets with perpendicular magnetic anisotropy via nonlinear magnon
processes. We identify magnon localisation and coalescence processes, whereby localised …

We identify both localisation and coalescence regimes, whereby localised magnetic textures
nucleate and subsequently evolve in accordance with a power law formalism. Coalescence
is observed for optical excitations both above and below the switching threshold.
Simulations indicate that the ultrafast generation of noncollinear magnetisation via optical
pumping establishes exchange-mediated spin currents with an equivalent 100% spin
polarised charge current density of 108 A/cm2. Such large spin currents precipitate rapid …