  It is shown that in spin injection experiments the interplay between external
magnetic field and alternating current can be observed already on a single
ferromagnet/normal metal interface. The interface resistance is predicted to
exhibit prominent features whenever the frequency of spin precession in the
applied field becomes equal to the frequency of the driving current. Using
these features, material-specific g-factors of electrons in normal metals can
be measured with less effort, albeit also with less precision.
