  Increasing evidence suggests that cosmological sheets, filaments, and voids
may be substantially magnetized today. The origin of magnetic fields in the
intergalactic medium (IGM) is, however, currently uncertain. It seems well
known that non-standard extensions to the physics of the standard model can
provide mechanisms susceptible of magnetizing the universe at large. Perhaps
less well known is the fact that standard, classical physics of
matter--radiation interactions actually possesses the same potential. We
discuss a magnetogenesis mechanism based on the exchange of momentum between
hard photons and electrons in an inhomogeneous IGM. Operating in the
neighborhood of ionizing sources during the epoch of reionization, this
mechanism is capable of generating magnetic seeds of relevant strengths over
scales comparable to the distance between ionizing sources. In addition,
summing up the contributions of all ionizing sources and taking into account
the distribution of gas inhomogeneities, we show that this mechanism leaves the
IGM, at the end of reionization, with a level of magnetization that might
account, when amplification mechanisms take over, for the magnetic fields
strengths in the current cosmic web.
