Spin dependent transport in Co nano-scale tunnel junctions

Abstract: Ferromagnetic tunnel junctionshave been fabricated, measured and theoretically described. Anoverview of the Julliere model, and Slonczewski's model todescribe the resistance change due to di®erent orientationof the magnetization between the magnetic electrodes(magnetoresistance) is given. Then a double-junctionconfiguration is theoretically analyzed in the sense of localspin accumulation related to the length an electron can travelbefore relaxing its spin. The analysis shows that thee®ect of spin accumulation contributes with a very smallor negligiblechange of the magnetoresistance for adouble-junction with large resistive barriers, and biased witha small voltage compared with a simple two-resistors-in-seriesmodel. Single-, triple-, and five- junction arrays werefabricated and measured. In order to analyze the spinaccumulation e®ect a double-junction with three terminalswas fabricated and measured to enable measurement of eachjunction of the double junction individually. Thedouble-junction configuration did not show any additionalmagnetoresistance over the two-junctions-in-series value at lowvoltage bias. However, the magnetoresistance of adouble-junction exhibited a weaker dependence on the biasvoltage than that expected for two junctions in series.