  We investigate metal-insulator transitions on an interacting two-dimensional
Dirac fermion system using the determinant quantum Monte Carlo method. The
interplay between Coulomb repulsion, disorder and magnetic fields, drives the
otherwise semi-metallic regime to insulating phases exhibiting different
characters. In particular, with the focus on the transport mechanisms, we
uncover that their combination exhibits dichotomic effects. On the one hand,
the critical Zeeman field $B_c$, responsible for triggering the band-insulating
phase due to spin-polarization on the carriers, is largely reduced by the
presence of the electronic interaction and quenched disorder. On the other
hand, the insertion of a magnetic field induces a more effective localization
of the fermions, facilitating the onset of Mott or Anderson insulating phases.
Yet these occur at moderate values of $B$, and cannot be explained by the full
spin-polarization of the electrons.
