  We suggest a model of synthetic ferrimagnetic semiconductor structure based
on GaAs-AlGaAs quantum well doped by two Mn delta-layers. The coupling between
the delta-layers is mediated by extra holes, and can be switched between ferro-
and antiferromagnetic one by gating the structure. A proper choice of Mn
concentrations in the delta-layers and of local degree of disorder enables
fabrication of a ferrimagnetic structure supporting ultrafast switching of
magnetization by short pulses of electric bias without an external magnetic
field. The switching mechanism in the structure relies on kinetic spin exchange
between the two delta-layers which is mediated by exchange scattering of
electric-pulse heated holes by magnetic ions within the layers. Owing to
specific interplay between characteristics of the exchange scattering, spin
decay times, and the heat withdraw in the suggested synthetic ferrimagnetic
semiconductor, the necessary parameters of electric-bias pulse are within the
technologically accessible range, and do not contradict typical thermal
kinetics of semiconductor structures.
