  The radio pulsar models based on the existence of an inner accelerating gap
located above the polar cap rely on the existence of a small scale, strong
surface magnetic field $B_s$. This field exceeds the dipolar field $B_d$,
responsible for the braking of the pulsar rotation, by at least one order of
magnitude. Neither magnetospheric currents nor small scale field components
generated during neutron star's birth can provide such field structures in old
pulsars. While the former are too weak to create $B_s \gtrsim 5\times
10^{13}$G$\;\gg B_d$, the ohmic decay time of the latter is much shorter than
$10^6$ years. We suggest that a large amount of magnetic energy is stored in a
toroidal field component that is confined in deeper layers of the crust, where
the ohmic decay time exceeds $10^7$ years. This toroidal field may be created
by various processes acting early in a neutron star's life. The Hall drift is a
non-linear mechanism that, due to the coupling between different components and
scales, may be able to create the demanded strong, small scale, magnetic spots.
Taking into account both realistic crustal microphysics and a minimal cooling
scenario, we show that, in axial symmetry, these field structures are created
on a Hall time scale of $10^3$-$10^4$ years. These magnetic spots can be
long-lived, thereby fulfilling the pre-conditions for the appearance of the
radio pulsar activity. Such magnetic structures created by the Hall drift are
not static, and dynamical variations on the Hall time scale are expected in the
polar cap region.
