  We investigate the effects of spin-polarized leads on the Kondo physics of a
quantum dot using the numerical renormalization group method. Our study
demonstrates in an unambiguous way that the Kondo effect is not necessarily
suppressed by the lead polarization: While the Kondo effect is quenched for the
asymmetric Anderson model, it survives even for finite polarizations in the
regime where charge fluctuations are negligible. We propose the linear
tunneling magnetoresistance as an experimental signature of these behaviors. We
also report on the influence of spin-flip processes.
