Relation between Julliere and Slonczewski models of tunneling magnetoresistance

Using the Slonczewski model with a $\delta$-type potential barrier, we study spin-dependent tunneling conductances in a tunnel junction composed of two ferromagnetic layers (FM’s) separated by an insulating barrier (I). In the high barrier case, the expression for the tunneling magnetoresistance is found to have the same form as that proposed by Julliere, but the electron-spin polarizations in both models have different definitions. We suggest that the spin dependence of the transmission coefficient should be taken into account in a FM/I/FM tunnel junction, and so the present formula can better describe its tunneling magnetoresistance.