  The density of states of the two-dimensional fermionic Hubbard model in the
perpendicular homogeneous magnetic field is calculated using the strong
coupling diagram technique. The density of states at the Fermi level as a
function of the inverse magnetic induction oscillates, and the frequency of
these oscillations increases by an order of magnitude with the change of the
deviation from half-filling from small to moderate values. This frequency
variation is caused by the change of Landau subbands contributing to the
density -- in the former case they are at the periphery of the Landau spectrum,
while in the latter case the dominant contribution is provided by bands near
its center. With changing induction these groups of bands behave differently.
For small deviations from half-filling the calculated oscillation frequency is
comparable to that observed in quantum oscillation experiments in yttrium
cuprates.
