For example, a tunnel barrier at the interface may work as such a spin-dependent interface resistance. If the inserted interface resistance is sufficiently larger than the spin resistances, the polarization of the injected current will be determined by the spin asymmetry of the interface resistance, γl:
Spin polarization of the injected current = –  |
(17) |
In addition, spin accumulation is governed by the interface resistance as follows:
|
(18) |
A large spin accumulation in the semiconductors can be expected using a tunnel barrier. Motsnyi et al. [9] reported the successful injection of spin-polarized current from the CoFe FM to the GaAs semiconductor layer through an AlOx barrier. They also confirmed it by showing precession of the injected spins under an applied magnetic field with an oblique angle by again observing the polarization of the emitted light. In addtion, many research groups proven the spins injection into III–V semiconductors by detecting the polarization of the emitted light [1,10]. Another type of measurement called "non-local MR measurement", the detection of the spin dependent chemical potential using a second ferromagnetic electrode was used to prove the spin injection into NM metals.
References:
[1]. Y. Ohno, et al, Nature 402 (1999) 790.
[2]. F.J. Jedema, et al, Nature 410 (2001) 345 ; 416 (2002) 713.
[3]. I. Appelbaum, B. Huang, and D.J. Monsma, Nature 447 (2007) 295.
[4]. J.C. Slonczewski, J. Magn. Magn. Mater. 195 (1999) L261.
[5]. E.B. Myers, et al, Science 285 (1999) 867.
[6]. G. Schmidt, et al, Phys. Rev. B 62 (2000) R4790.
[7]. R. Fiederling, et al, Nature 402 (1999) 787.
[8]. E.I. Rashba, Phys. Rev. B 62 (2000) R16267.
[9]. V.F. Motsnyi, et al, Appl. Phys. Lett. 81 (2002) 265.
[10]. B.T. Jonker, et al, Nat. Phys. 3 (2007) 542.
Quiz 11:
(Q11.1). What are the factors determine the spin injection efficiency?
(Q11.2). Why does the spin accumulate at the interface between the ferromagnetic and nonmagnetic?
(Q11.3). How can we control the spin polarization of the injected current?
(Q11.4). How do we achieve large spin accumulation in the semiconductor?