On the importance of defects in magnetic tunnel junctions

The interpretation of junction magnetoresistance results of ferromagnet/insulator/ferromagnet structures must consider a number of complications. These complications include spin polarized defects within the nonmagnetic dielectric layer, and the recognition that; many metal to metal oxide interfaces often involve further oxidation and reduction making such interfaces very heterogeneous. The possibility of spin-polarized defects in the barrier layer is important as large values of magnetoresistance may result that, have little to do with the ferromagnetic polarization. Interlayer exchange coupling between two ferromagnetic films, separated by a nonmagnetic nonmetallic spacer (semiconductor and insulator materials) can also occur. This coupling is distinct from the very low temperature tunneling phenomena between two ferromagnets, through a dielectric spacer layer, as the coupling is sometimes oscillatory. As an illustration, the ferromagnetic coupling between Co and CrO2, through in insulator (Cr2O3) may be related to defect states in the insulating barrier layer.