Oscillating tunneling magnetoresistance in magnetic double-tunnel-junction structures

Abstract

Based on an extended Slonczewski model with double $\ensuremath{\delta}$-type potential barriers, we study spin-dependent resonant tunneling conductances in a double-tunnel-junction structure, in which two ferromagnetic electrodes are separated from a middle nonmagnetic layer of thickness a by two thin insulating layers, respectively. It is shown that as the thickness a is increased, the tunneling magnetoresistance, along with the tunneling conductance for parallel and antiparallel magnetization configurations, exhibits amplitude-varying oscillating behavior with a period of $a=\ensuremath{\pi}{/k}_{F} {(k}_{F}$ being the Fermi wave vector). This abnormal phenomenon is found to stem from the spin-dependent resonant transmission of electrons passing through the double-tunnel-junction structure.