  Large scale primordial magnetic fields (PMFs) threading the intergalactic
medium are observed ubiquitously in the Universe playing a key role in the
cosmic evolution. Their origin is still debated constituting a very active
field of research. In the present article, we propose a novel natural ab initio
mechanism for the origin of such PMFs through the portal of supermassive
primordial black holes (PBHs) forming between the Big Bang Nucleosynthesis and
the recombination era. In particular, by considering PBHs furnished with a
locally isothermal disk we study the generation of a Biermann battery induced
seed magnetic field (MF) due to the vortexlike motion of the primordial plasma
around the black hole. Finally, by considering monochromatic PBH mass
distributions and deriving the relevant MF power spectrum we make a
conservative estimate for the seed PMF in intergalactic scales and at redshift
$z=30$, when typical galaxies are considered to form, which reads as $B\simeq
10^{-30}\mathrm{G}\left(\frac{\ell_\mathrm{R}}{10^6}\right)^2\left(\frac{M_\mathrm{PBH}}{10^{14}M_\odot}\right)^{5/2}$,
where $M_\mathrm{PBH}$ is the PBH mass and $\ell_\mathrm{R}\equiv
R_\mathrm{d}/R_\mathrm{ISCO}$, is the ratio of the radius of the disk,
$R_\mathrm{d}$ over the radius of the innermost stable circular orbit,
$R_\mathrm{ISCO}$. Interestingly enough, by requiring to seed a PMF of the
order of $10^{-30}\mathrm{G}$ necessary to give rise to a present day
$10^{-18}\mathrm{G}$ in intergalactic scales, we find a lower bound on the PBH
mass within the range $[10^{10}- 10^{16}]M_\odot$ depending on the radius of
the PBH disk.
