  Black holes immersed in magnetic fields are believed to be important systems
in astrophysics. One interesting topic on these systems is their superradiant
stability property. In the present paper, we analytically obtain the
superradiantly stable regime for the asymptotically flat dyonic
Reissner-Nordstrom black holes with charged massive scalar perturbation. The
effective potential experienced by the scalar perturbation in the dyonic black
hole background is obtained and analyzed. It is found that the dyonic black
hole is superradiantly stable in the regime $0<r_{-}/r_{+}<2/3$, where $r_\pm$
are the event horizons of the dyonic black hole. Compared with the purely
electrically charged Reissner-Nordstrom black hole case, our result indicates
that the additional coupling of the charged scalar perturbation with the
magnetic field makes the black hole and scalar perturbation system more
superradiantly unstable, which provides further evidence on the instability
induced by magnetic field in black hole superradiance process.
