具有AlN和ZnO间隔层的Fe基和Co基磁性隧道结
Fe- and Co-based magnetic tunnel junctions with AlN and ZnO spacers
摘要：
AlN和ZnO是两种广泛应用于显示器行业的宽带隙半导体，它们以纤锌矿结构结晶，这有利于形成紧密堆积的普通铁磁体的外延界面。在这里，我们探讨这些半导体材料的磁性隧道结绝缘屏障。特别地，{ \it ab initio}量子输运代码{ \it Smeagol}用于对$X$ [111]/ $Y$ [0001]/ $X$ [111]（$X=$ Co和Fe、$Y=$ AlN和ZnO）结族进行建模。这两种半导体显示具有$p$轨道特征的价带顶，而导带底具有$s$型对称性。禁带中沿[0001]方向的最小复带衰减系数与$Δ_1$对称性相关，并在二维布里渊区的$Γ$点处跨带隙连接。该特征使得能够进行自旋过滤并且可以导致大的隧穿磁阻。在一般情况下，我们发现，钴基结呈现有限的自旋过滤和小的磁阻在低偏压下，因为两个自旋子带交叉的费米能级与$Δ_1$对称性。这与Fe的情况形成对比，其中仅少数$Δ_1$谱带可用。然而，即使在Fe的情况下，在低偏压下的磁阻的幅度仍然相对较小，主要是由于远离$Γ$点并且通过具有不同于$Δ_1$的对称性的复杂带的传导。唯一的例外是Fe/AlN/Fe结，我们预测在低偏压下的磁阻约为1，000\%。
英文摘要：
AlN and ZnO, two wide band-gap semiconductors extensively used in the display industry, crystallise in the wurtzite structure, which can favour the formation of epitaxial interfaces to close-packed common ferromagnets. Here we explore these semiconductors as material for insulating barriers in magnetic tunnel junctions. In particular, the {\it ab initio} quantum transport code {\it Smeagol} is used to model the $X$[111]/$Y$[0001]/$X$[111] ($X=$ Co and Fe, $Y=$ AlN and ZnO) family of junctions. Both semiconductors display a valance-band top with $p$-orbital character, while the conduction band bottom exhibits $s$-type symmetry. The smallest complex-band decay coefficient in the forbidden energy-gap along the [0001] direction is associated with the $Δ_1$ symmetry, and connects across the band gap at the $Γ$ point in 2D Brillouin zones. This feature enables spin filtering and may result in a large tunnelling magnetoresistance. In general, we find that Co-based junctions present limited spin filtering and little magnetoresistance at low bias, since both spin sub-bands cross the Fermi level with $Δ_1$ symmetry. This contrasts the situation of Fe, where only the minority $Δ_1$ band is available. However, even in the case of Fe the magnitude of the magnetoresistance at low bias remains relatively small, mostly due to conduction away from the $Γ$ point and through complex bands with symmetry different than $Δ_1$. The only exception is for the Fe/AlN/Fe junction, where we predict a magnetoresitance of around 1,000\% at low bias.
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