  We observed slow relaxation of magnetoresistance in quantum well structures
GaAs-AlGaAs with a selective doping of both wells and barrier regions which
allowed partial filling of the upper Hubbard band. Such a behavior is explained
as related to magnetic-field driven redistribution of the carriers between
sites with different occupation numbers due to spin correlation on the doubly
occupied centers. This redistribution, in its turn, leads to slow
multi-particle relaxations in the Coulomb glass formed by the charged centers.
