CHARGE AND SPIN TRANSPORT THROUGH A METALLIC FERROMAGNETIC-PARAMAGNETIC-FERROMAGNETIC JUNCTION

Using a pair of weakly coupled drift-diffusion equations for spin-up a nd spin-down electrons, we compute the signal of recent spin-injection experiments by Johnson on ferromagnetic-paramagnetic-ferromagnetic fi lms. In the limit of large junction resistance, our results coincide w ith those of earlier calculations. As the junction resistance decrease s, there are correction terms which provide a cutoff to the size of th e signal for films much thinner than the spin-diffusion length. The ph ysical origin of this cutoff is the leakage of nonequilibrium magnetiz ation out of the paramagnet into the current and voltage probes. Altho ugh our calculation can explain the sample thickness dependence of the experiments, it cannot account for the large magnitude of the signal observed.