  Irradiating solids with ultrashort laser pulses is known to initiate
femtosecond timescale magnetization dynamics. However, sub-femtosecond spin
dynamics have not yet been observed or predicted. Here, we explore ultrafast
light-driven spin dynamics in a highly non-resonant strong-field regime.
Through state-of-the-art ab-initio calculations, we predict that a non-magnetic
material can be transiently transformed into a magnetic one via dynamical
extremely nonlinear spin-flipping processes, which occur on attosecond
timescales and are mediated by a combination of multi-photon and spin-orbit
interactions. These are non-perturbative non-resonant analogues to the inverse
Faraday effect that build up from cycle-to-cycle as electrons gain angular
momentum. Remarkably, we show that even for linearly polarized driving, where
one does not intuitively expect any magnetic response, the magnetization
transiently oscillates as the system interacts with light. This oscillating
response is enabled by transverse anomalous light-driven currents in the solid,
and typically occurs on timescales of ~500 attoseconds. We further demonstrate
that the speed of magnetization can be controlled by tuning the laser
wavelength and intensity. An experimental set-up capable of measuring these
dynamics through pump-probe transient absorption spectroscopy is outlined and
simulated. Our results pave the way for new regimes of ultrafast manipulation
of magnetism.
