用自旋相关隧穿探测贵金属掺杂钴的长程磁邻近效应
Long-ranged magnetic proximity effects in noble metal-doped cobalt probed with spin- dependent tunnelling
摘要：
我们在溅射的AlOx基磁性隧道结和Meservey-Tedrow结中插入Au和Cu的非磁性层，以研究它们对隧道磁电阻（TMR）和自旋极化（TSP）的影响。当Au或Cu被插入到Co/AlOx界面中时，我们发现TMR和TSP对于高达几纳米的厚度仍然是有限的和可测量的。高分辨率透射电子显微镜显示，当Cu和Au界面层的厚度超过~3 nm时，它们是完全连续的，这意味着自旋极化载流子穿透界面贵金属的距离超过该值。一个幂律模型的基础上交换散射被发现更适合的数据比一个现象学的指数衰减。这些长度尺度之间的差异和短得多的报道从X射线磁性圆二色性研究磁proximitization归因于这样一个事实，即我们的隧道传输测量选择性地探测类s电子接近费米能级。当在Co中插入0.1 nm厚的Cu或Au层时，我们发现TMR和TSP的抑制在<=1 nm的长度尺度上恢复，表明这是足够量的Co以在与隧道势垒的界面处形成完全自旋极化的能带结构。
英文摘要：
We inserted non-magnetic layers of Au and Cu into sputtered AlOx-based magnetic tunnel junctions and Meservey-Tedrow junctions in order to study their effect on tunnelling magnetoresistance (TMR) and spin polarization (TSP). When either Au or Cu are inserted into a Co/AlOx interface, we find that TMR and TSP remain finite and measurable for thicknesses up to several nanometres. High-resolution transmission electron microscopy shows that the Cu and Au interface layers are fully continuous when their thickness exceeds ~3 nm, implying that spin-polarized carriers penetrate the interface noble metal to dis- tances exceeding this value. A power law model based on exchange scattering is found to fit the data better than a phenomenological exponential decay. The discrepancy between these length scales and the much shorter ones reported from x-ray magnetic circular dichroism studies of magnetic proximitization is ascribed to the fact that our tunnelling transport measurements selectively probe s-like electrons close to the Fermi level. When a 0.1 nm thick Cu or Au layer is inserted within the Co, we find that the suppression of TMR and TSP is restored on a length scale of <=1 nm, indicating that this is a sufficient quantity of Co to form a fully spin-polarized band structure at the interface with the tunnel barrier.
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