  We introduce the concept of a spintronic effective mass for spin-polarized
carriers in semiconductor structures, which arises from the strong
spin-polarization dependence of the renormalized effective mass in an
interacting spin-polarized electron system. The majority-spin many-body
effective mass renormalization differs by more than a factor of 2 at rs=5
between the unpolarized and the fully polarized two-dimensional system, whereas
the polarization dependence (~15%) is more modest in three dimensions around
metallic densities (rs~5). The spin-polarization dependence of the carrier
effective mass is of significance in various spintronic applications.
