  Spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for
spin currents in metals and semiconductors. We discuss the power loss due to
SCD in potential spintronics devices and analyze in detail the associated
damping of collective spin-density excitations. It is found that SCD
contributes substantially to the linewidth of intersubband spin plasmons in
parabolic quantum wells, which suggests the possibility of a purely optical
quantitative measurement of the SCD effect by means of inelastic light
scattering.
