  In this study, we examine the magnetic field evolution occurring in a neutron
star crust. Beyond the elastic limit, the lattice ions are assumed to act as a
plastic flow. The Ohmic dissipation, Hall drift, and bulk fluid velocity driven
by the Lorentz force are considered in our numerical simulation. A magnetically
induced quadrupole deformation is observed in the crust during the evolution.
Generally, the ellipticity decreases as the magnetic energy decreases. In a
toroidal-field-dominated model, the sign of the ellipticity changes. Namely,
the initial prolate shape tends to become oblate. This occurs because the
toroidal component decays rapidly on a smaller timescale than the poloidal
dipole component. We find that the magnetic dipole component does not change
significantly on the Hall timescale of $\sim 1$Myr for the considered simple
initial models. Thus, a more complex initial model is required to study the
fast decay of surface dipoles on the abovementioned timescale.
