  We present a model for the seeding and evolution of magnetic fields in
galaxies by supernovae (SN). SN explosions during galaxy assembly provide seed
fields, which are subsequently amplified by compression, shear flows and random
motions. Our model explains the origin of microG magnetic fields within
galactic structures. We implement our model in the MHD version of the
cosmological simulation code Gadget-3 and couple it with a multi-phase
description of the interstellar medium. We perform simulations of Milky
Way-like galactic halo formation and analyze the distribution and strength of
the magnetic field. We investigate the intrinsic rotation measure (RM)
evolution and find RM values exceeding 1000 rad/m*m at high redshifts and RM
values around 10 rad/m*m at present-day. We compare our simulations to a
limited set of observational data points and find encouraging similarities. In
our model, galactic magnetic fields are a natural consequence of the very basic
processes of star formation and galaxy assembly.
