  Neutral test particles around a Schwarzschild black hole immersed in an
external uniform magnetic field have no interactions of electromagnetic forces,
but their motions can be chaotic. This chaotic behavior is induced owing to the
gravitational effect of the magnetic field leading to the nonintegrability of
the magnetized Ernst-Schwarzschild spacetime geometry. In fact, chaos is
strengthened typically with an increase of the energy or the magnetic field
under appropriate circumstances. When these test particles have charges, the
electromagnetic forces are included. As a result, the electromagnetic forces
have an effect on strengthening or weakening the extent of chaos caused by the
gravitational effect of the magnetic field.
