Spin-polarized tunneling through a thin-film

Abstract

The effect of spin-disorder scattering on perpendicular transport in a magnetic monolayer is considered within the single-site Coherent Potential Approximation (CPA). The exchange interaction between a conduction electron and localized moment of the magnetic ion is treated with the use of the sf model. Electron-spin polarization is evaluated in the tunnel current which comes from the different densities of spin-up, spin-down conduction electrons at the Fermi level in a ferromagnetic semiconductor (EuS). Calculated results are compared with some tunneling experiments.

Spin-polarized tunneling in ferromagnetic double barrier junctions

“…Thus the magnitude of the spin polarization for tunneling density of states in each layer can be given by [6,16] …”

“…When an s-electron is propagating in the FMS layers it will subject to different effective potentials through the s-f exchange interaction according to the orientation of its spin. In order to treat the exchange scattering of the s-electron within the framework of the single-site CPA, we consider a single f-spin located at site r in an effective layered medium where an s-electron is subjected to a complex potential (or coherent potential) which is site diagonal and takes the value Σ ↑ or Σ ↓ , according to the spin orientation of the s-electron [6]. Therein, an s-electron moving in this effective medium can be described by the effective Hamiltonian K in the Bloch-Wannier representation as…”

“…As in Refs. [6,9], we apply the condition that the average scattering of the selectron by the single f-spin in the medium is zero. Thus we define the single-site t-matrix of the s-f exchange interaction as…”

“…In order to study the tunneling spin polarization, we assume that N ↑ /N ↓ is equal to D n↑ (E)/D n↓ (E), where N ↑ (N ↓ ) is the number of electrons with up (down) spin after tunneling to the FMS conduction band, D n↑ (E)(D n↓ (E)) is the LDOS with up (down) spin at the nth layer, and E is a typical energy of the tunneling electrons. Thus the magnitude of the spin polarization for tunneling density of states in each layer can be given by [6,16]…”

“…The spin-polarized tunneling phenomenon, showed that spin is conserved in the tunneling process and the electrons coming from a ferromagnet are spin-polarized [3]. In the last decade, with the progress in the research on magnetic multilayers, spinpolarized tunneling through magnetic semiconductor (MS) layers has received increasing attention [4][5][6]. In tunneling experiments, when a FMS is used as a tunnel barrier, the conduction band splits into up spin and down spin subbands and the barrier height for these two subbands is changed.…”