Understanding the bias dependence of magnetoresistance in the system La/sub 0.7/Sr/sub 0.3/MnO/sub 3//SrTiO/sub 3//Co

Summary form only given. In the six years of renewed activity, the field of magnetic tunnel junctions has matured slowly, fueled by junctions integrating an amorphous barrier of Al/sub 2/O/sub 3/ yet hindered by the experimental difficulty of producing epitaxial junctions which are accessible in a theoretical approach. The nearly ideal system, comprised of a half-metallic manganite electrode of La/sub 0.7/Sr/sub 0.3/MnO/sub 3/[001] with only a d?? band crossing the Fermi level, grown in an epitaxial bilayer with an insulating barrier of SrTiO/sub 3/[001] which allows efficient transmission of d electronic states and capped with a counterelectrode such as Co with a [111] texture, has already proven itself to be an interesting candidate for fundamental tunneling studies. With an intent to explain the unique features in the bias dependence of the magnetoresistance for such a system, we have performed inverse photoemission experiments to determine the possible influence of the spin-polarized unoccupied density of states of La/sub 0.7/Sr/sub 0.3/MnO/sub 3/ [001]. Then, with an aim to investigate the influence of the Co density of stalest we present a set of comparative tunneling experiments on junctions with a counterelectrode of CoCr-Cr impurities introduce virtual bound states in the Co matrix density of states, and thus affect in a controlled manner the resulting bias dependence of the magnetoresistance. The role of the crystallinity of the SrTiO/sub 3/ barrier is also discussed using La/sub 0.7/Sr/sub 0.3/MnO/sub 3/-based junctions which integrate an amorphous barrier of SrTiO/sub 3/.