The decay of a strong magnetic field in a conducting matter is considered.
It is shown that nondissipative Hall currents can considerably change the b
ehavior of the field when it decays. The nonlinear character of the Hall ef
fect leads to the generation of fields of high multipolarity even for most
simple initial magnetic configurations. In particular, the evolution of an
initially dipole configuration may give rise not only to quadrupole or high
er poloidal harmonics but also to a toroidal field that is other than zero
only inside the conductor. The nonlinear Hall currents relate different har
monics to each other and, in a sufficiently strong field, may provide effic
ient energy exchange between them. Due to this redistribution of the magnet
ic energy, the evolution of different harmonics has an oscillating characte
r. The oscillation period is determined by the characteristic time of Hall
drift and may be fairly short in strong magnetic fields. (C) 2000 MAIK "Nau
ka/Interperiodica".