Theory of tunneling magnetoresistance of Fe/GaAs/Fe(001) junctions
Theory of tunneling magnetoresistance of Fe/GaAs/Fe(001) junctions
复制标题
DOI：
10.1103/physrevb.82.115212
复制
发表时间：
2010-09
影响因子：
3.7
通讯作者：
G. Autès;J. Mathon;A. Umerski
中科院分区：
文献类型：
--
作者：
G. Autès;J. Mathon;A. Umerski
本文从理论上研究了自旋轨道相互作用下外延Fe/GaAs/Fe（001）隧道结的自旋相关输运。在忽略自旋轨道相互作用和d轨道对GaAs能带结构影响的情况下，计算结果表明，隧穿磁电阻（TMR）随GaAs势垒厚度的增加而增大，并接近理想自旋阀极限。然而，当d轨道，特别是自旋-轨道相互作用，包括TMR比饱和GaAs厚度迅速到一个相当温和的值约30%时，费米能级EF位于中间的GaAs间隙。这个出乎意料的小值不能单独用自旋轨道相互作用来解释。结果表明，其根本原因是存在的少数自旋带结构的Fe/GaAs/Fe三层靠近中心的差距的共振。研究了GaAs势垒高度（费米能级EF在差距中的位置）对隧道磁电阻的影响，结果表明，当费米能级EF位于少数自旋通道的共振处时，理想结的隧道磁电阻会大大增强。然而，我们发现，任何小的不对称的结删除TMR峰，并减少TMR到小的值，为50%的顺序，对于一个相当大的间隔的值的EF在附近的GaAs间隙的中间。因此，我们得出结论，自旋-轨道耦合导致饱和的TMR与GaAs厚度，但饱和值是由共振的存在。
We investigate theoretically spin-dependent transport through an epitaxial Fe/GaAs/Fe(001) tunnel junction with and without spin-orbit interaction. Calculations neglecting spin-orbit interaction and the effect of d orbitals on the GaAs band structure predict that the tunneling magnetoresistance (TMR) should increase with increasing thickness of GaAs barrier and approach values close to the perfect spin-valve limit. However, when d orbitals and, in particular, spin-orbit interaction is included the TMR ratio saturates rapidly with GaAs thickness to a rather modest value of about 30% when the Fermi level E F lies in the middle of the GaAs gap. This unexpectedly small value cannot be explained by spin-orbit interaction alone. It is shown that the underlying reason for this is the presence of a resonance in the minority-spin band structure of the Fe/GaAs/Fe trilayer lying close to the center of the gap. Investigation of the dependence of the TMR on the height of the GaAs barrier (position of the Fermi energy EF in the gap) shows that the TMR of a perfect junction is strongly enhanced when EF lies at the resonance in the minority-spin channel. However, we show that any small asymmetry of the junction removes the TMR peak and reduces the TMR to small values, of the order of 50%, for a rather large interval of values of E F in the vicinity of the middle of the GaAs gap. We thus conclude that the spin-orbit coupling leads to saturation of the TMR with GaAs thickness, but the saturation value is determined by the presence of the resonance.