  Abrikosov vortex lattice dynamics in a superconductor with weak defects is
studied taking into account gyroscopic (Hall) properties. It is demonstrated
that interaction of the moving lattice with weak defects results in appearance
of the additional drag force, $F$, which is $F(V)\propto \sqrt V$ at small
velocities, while at high velocities $F(V)\propto 1/\sqrt V$. Thus, the total
drag force can be a nonmonotonic function of the lattice translational
velocity. It leads to the velocity dependence of the Hall angle and a nonlinear
current-voltage characteristic of the superconductor. Due to the Hall component
in the lattice motion, the value $[dF(V)/dV]^{-1}$ does not coincide with the
differential mobility $dV/dF_{e}$, where $F_{e}$ is the external force acting
on the lattice. The estimates suggest that condition $dV/dF_{e} < 0$ can be met
with difficulty in contrast to $dV/dF < 0$. The instability of the lattice
motion regarding nonuniform perturbations has been found when the value of
(-$dF/dV$) is greater than a certain combination of elastic modulii of the
vortex lattice, while the more strict requirement $dV/dF_{e} < 0$ is still not
fulfilled.
