  Ultrafast laser pulses provide unique tools to manipulate magnetization
dynamics at femtosecond timescales, where the interaction of the electric field
-- such as excitation of spin carriers to non-equilibrium states, generation of
localized charge currents, demagnetization, or inverse Faraday effect --
dominates over the magnetic field. Recent proposals using structured laser
beams have enlightened the possibility to generate intense femtosecond magnetic
fields, spatially isolated from the electric field. Here we demonstrate the
relevance of this novel scenario to femtomagnetism, unveiling the purely
precessional, non-linear, chiral response of the magnetization when subjected
to circularly polarized magnetic fields. This fundamental result not only opens
an avenue in the study of laser-induced ultrafast magnetization dynamics, but
also sustains technological implications as a route to promote all-optical
non-thermal magnetization switching both at shorter timescales -- towards the
attosecond regime -- and at THz frequencies.

Mesoscale and Nanoscale Physics