Quantum modeling of interfacial scattering effect on tunneling conductance spectra of magnetic tunnel junction with ferromagnet/insulator/insulator/ferromagnet

Abstract

The tunneling conductance spectroscopy of ferromagnet/insulator/insulator/ferromagnet junctions with parallel (P) and anti-parallel (AP) alignments of the magnetization directions were theoretically studied based on a scattering method in a one-dimensional system. Due to the junctions in a real experiment being composed of, for example, Fe/ZnO/MgO/Fe materials, in this work the two ferromagnetic electrodes were modeled to be the same, but the two insulating sheets were set to be distinguishable. As the main area of interest was to focus on the effects of the interfacial scattering on the transport behavior, the potential strength at the three interfaces was included in both non-spin–flip (Z) and spin–flip (Zf) scattering based on the Dirac-delta potential model, and all of them were set to be different in magnitude. This means that there are Z1(2)(3) and Zf1(2)(3) for the first, second, and third interfaces. It was found that the potential strength at the first interface (Z1) plays a crucial role in determining the direct transmission or oscillation behavior. For the effect of Zf , an increase in Zf1 causes the oscillatory behavior to increase, while the direct transmission is most prominent when Zf2 or Zf3 increases. For the effect of the insulating band gaps (Ui), the condition for direct transmission is U2≥3U1, where U1(2) is the insulating band gap of the first and second insulators, respectively. Finally, if the electron effect masses of all materials in the junction are approximately equal, then the direct transmission process can occur.