Oscillating tunneling magnetoresistance in magnetic double-tunnel-junctionstructures

Based on an extended Slonczewski model with double delta-type potential bar riers, we study spin-dependent resonant tunneling conductances in a double- tunnel-junction structure, in which two ferromagnetic electrodes are separa ted from a middle nonmagnetic layer of thickness a by two thin insulating l ayers, respectively. It is shown that as the thickness a is increased, the tunneling magnetoresistance, along with the tunneling conductance for paral lel and antiparallel magnetization configurations, exhibits amplitude-varyi ng oscillating behavior with a period of a = pi/k(F) (k(F) being the Fermi wave vector). This abnormal phenomenon is found to stem from the spin-depen dent resonant transmission of electrons passing through the double-tunnel-j unction structure. [S0163-1829(99)00122-8].