  Evidence repeatedly suggests that cosmological sheets, filaments and voids
may be substantially magnetised today. The origin of magnetic fields in the
intergalactic medium is however currently uncertain. We discuss a
magnetogenesis mechanism based on the exchange of momentum between hard photons
and electrons in an inhomogeneous intergalactic medium. Operating near ionising
sources during the epoch of reionisation, it is capable of generating magnetic
seeds of relevant strengths over scales comparable to the distance between
ionising sources. Furthermore, when the contributions of all ionising sources
and the distribution of gas inhomogeneities are taken into account, it leads,
by the end of reionisation, to a level of magnetisation that may account for
the current magnetic fields strengths in the cosmic web.
