  We study non-equilibrium electronic transport through a quantum dot or
impurity weakly coupled to ferromagnetic leads. Based on the rate equation
formalism we derive noise spectra for the transport current. We show that due
to quantum interference between different spin components of the current the
spectrum develops a peak or a dip at the frequency corresponding to Zeeman
splitting in the quantum dot. The detailed analysis of the spectral structure
of the current is carried out for noninteracting electrons as well as in the
regime of Coulomb blockade.
