Department of Physics, New York University, New York, NY 10003 USA

Mechanisms that produce resistivity due to domain walls in ferromagnetic metals will be reviewed; attention will be focused on the mixed spin character of the electron eigenstates in these walls, and the usual spin dependent scattering due to impurities. At low temperatures the impurity scattering does not flip the spin of conduction electrons, so that the spin-up and spin-down currents in the domains are independent. However in the walls the same scattering mixes these currents due to the spin character of the current carrying states in the noncollinear wall geometry. The effect of this mixing is to increase resistivity due to impurity scattering in walls above that which is produced in the domains themselves.

The factors that govern the magnetoresistance of magnetic tunnel junctions will be reviewed. Attention will be focused on: the character of the orbitals that bond at the interfaces between electrodes and the insulating barrier, and the effect of electric fields on redistributing the electron charge and spin distribution at the interfaces, i.e., changing the profile of the tunnel barrier. While the effects of electric field penetration in the metallic electrodes was appreciated as early as the 1960's, we find that: 1) the field induced redistribution is larger for the electrons that spill out of the electrode at the interface into the insulating barrier, and 2) the induced changes in charge in the majority and minority spin channels in the electrode go in opposite directions, so as to produce important changes in the magnetization for relatively small changes in the charge at the interfaces.