有机半导体自旋阀结构中微结构与磁输运的相关性
Correlation between microstructure and magnetotransport in organic semiconductor spin valve structures
摘要：
我们研究了有机-无机杂化多层膜结中的磁输运。在这些器件中，有机半导体（OSC）Alq $_3$（三（8-羟基喹啉）铝）在铁磁（FM）Co和Fe层之间形成间隔层。Alq $_3$层的厚度为50-150 nm。在4.2 K下，在垂直于平面几何形状的电流中观察到正磁阻（MR），并且这些效应持续到室温。用X射线反射仪、俄歇电子能谱仪和极化中子反射仪（PNR）研究了器件的微观结构。该膜显示出在Alq $_3$和周围FM层之间的界面处具有适度平均化学粗糙度（3-5 nm）的良好限定的层。反射测量表明，较大的MR效应与较小的FM/Alq $_3$界面宽度（化学和磁性）和在Alq $_3$ /Fe界面的磁死层。PNR数据还表明，Co层，这是沉积在顶部的Alq $_3$，采用多畴的磁性结构在低场和一个完美的反平行状态没有得到。所观察到的MR的起源进行了讨论，并归因于自旋相干传输。在80 K下，Alq $_3$中自旋扩散长度的下限估计为$43 \pm 5$ nm。然而，微观结构和磁输运之间的微妙的相关性表明在这些系统中的界面效应的重要性。
英文摘要：
We have studied magnetotransport in organic-inorganic hybrid multilayer junctions. In these devices, the organic semiconductor (OSC) Alq$_3$ (tris(8-hydroxyquinoline) aluminum) formed a spacer layer between ferromagnetic (FM) Co and Fe layers. The thickness of the Alq$_3$ layer was in the range of 50-150 nm. Positive magnetoresistance (MR) was observed at 4.2 K in a current perpendicular to plane geometry, and these effects persisted up to room temperature. The devices' microstructure was studied by X-ray reflectometry, Auger electron spectroscopy and polarized neutron reflectometry (PNR). The films show well-defined layers with modest average chemical roughness (3-5 nm) at the interface between the Alq$_3$ and the surrounding FM layers. Reflectometry shows that larger MR effects are associated with smaller FM/Alq$_3$ interface width (both chemical and magnetic) and a magnetically dead layer at the Alq$_3$/Fe interface. The PNR data also show that the Co layer, which was deposited on top of the Alq$_3$, adopts a multi-domain magnetic structure at low field and a perfect anti-parallel state is not obtained. The origins of the observed MR are discussed and attributed to spin coherent transport. A lower bound for the spin diffusion length in Alq$_3$ was estimated as $43 \pm 5$ nm at 80 K. However, the subtle correlations between microstructure and magnetotransport indicate the importance of interfacial effects in these systems.
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