  The Universe is pervaded by magnetic fields in different scales, although for
simplicity, they are ignored in most cosmological simulations. In this paper,
we use the TNG50, which is a large cosmological galaxy formation simulation
that incorporates magnetic fields with an unprecedented resolution. We study
the correlation of the magnetic field with various galaxy properties such as
the total, stellar and gaseous mass, circular velocity, size and star formation
rate. We find a linear correlation between the average magnetic field pervading
the disc of galaxies in relative isolation and their circular velocities. In
addition we observed that in this sample the average magnetic field in the disc
is correlated with the total mass as $\overline{B}\sim
M_{\mathrm{tot,\,R_{\star}}}^{0.2}$. We also find that the massive galaxies
with active wind-driven black hole feedback, do not follow this trend, as their
magnetic field is substantially affected by this feedback mode in the TNG50
simulation. We show that the correlation of the magnetic field with the star
formation rate is a little weaker than the circular velocity. Moreover, we
compare the magnetic field components of the above sample with a compiled
observational sample of non-cluster non-interacting nearby galaxies. Similar to
the observation, we find a coupling between the ordered magnetic field and the
circular velocity of the flat part of the rotation curve in the simulation,
although contrary to the observation, the ordered component is dominant in the
simulation.
