  In order to test the role of large-scale magnetic fields in quasiperiodic
oscillation phenomena observed in microquasars, we study oscillatory motion of
charged particles in vicinity of a Schwarzschild black hole immersed into an
external asymptotically uniform magnetic field. We determine the fundamental
frequencies of small harmonic oscillations of charged test particles around
stable circular orbits in the equatorial plane of a magnetized black hole, and
discuss the radial profiles of frequencies of the radial and latitudinal
harmonic oscillations in dependence on the mass of the black hole and the
strength of the magnetic field. We demonstrate that assuming relevance of
resonant phenomena of the radial and latitudinal oscillations of charged
particles at their frequency ratio $3:2$, the oscillatory frequencies of
charged particles can be well related to the frequencies of the twin
high-frequency quasi-periodic oscillations observed in the microquasars GRS
1915+105, XTE 1550-564 and GRO 1655-40.
