Theory of ultrahigh magnetoresistance achieved byk-space filtering without a tunnel barrier

Abstract

Calculations of the current-perpendicular-to-plane magnetoresistance (CPP GMR) of an epitaxial Fe/Ag/Fe(001) trilayer attached to an $n$-type InAs lead (collimator) are presented. They show that for realistic InAs carrier densities, the CPP GMR of this $k$-space selective system can reach peak values of 10${}^{5}$%. The very high values of the CPP GMR are achieved because the small Fermi surface of the semiconductor collimator selects only electrons traveling perpendicular to the Fe/Ag interface ($\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}$ point) where the magnetic contrast is as high as that of the Fe/MgO interface. The high calculated CPP GMR is very robust to disorder at the Fe/InAs interface and within the InAs layer itself. It is also much higher than the highest observed tunneling magnetoresistance of MgO-based junctions but the total resistance of the Fe/Ag/Fe trilayer with an InAs collimator is much lower than that of the tunneling junction. Nevertheless, the resistance is high enough to obviate the need for nanopillar geometry necessary for conventional CPP GMR systems.