  We theoretically analyzed the Andreev reflection in ferromagnetic
metal/nonmagnetic metal/superconductor double junctions with special attention
to the electron interference effect in the nonmagnetic metal layer. We showed
that the conductance oscillates as a function of the bias voltage due to the
geometrical resonance. We found that the exchange field, and therefore the spin
polarization of the ferromagnetic metal can be determined from the period of
the conductance oscillation, which is proportional to the square root of the
exchange field.
