  Yukawa interactions can mediate relatively long-range attractive forces
between fermions in the early universe. Such a globally attractive interaction
creates an instability that can result in the growth of structure in the
affected species even during the radiation dominated era. The formation and
collapse of fermionic microhalos can create hot fireballs at the sites of the
collapsing halos which inject energy into the cosmic plasma. In this paper we
study a new phenomena which can take place in such models. We show that the
injected energy can be partially converted into primordial magnetic fields and
we estimate the correlation scale and the power spectrum of these fields. We
show that they may be the seeds of the observed astrophysical magnetic fields.
