Zatko Victor, Dubois Simon M-M, Godel Florian, Galbiati Marta, Peiro Julian, Sander Anke, Carretero Cécile, Vecchiola Aymeric, Collin Sophie, Bouzehouane Karim, Servet Bernard, Petroff Frédéric, Charlier Jean-Christophe, Martin Marie-Blandine, Dlubak Bruno, Seneor Pierre
Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France.
Institute of Condensed Matter and Nanosciences (IMCN), Université Catholique de Louvain (UCLouvain), B-1348 Louvain-la-Neuve, Belgium.
ACS Nano. 2022 Sep 27;16(9):14007-14016. doi: 10.1021/acsnano.2c03625. Epub 2022 Sep 6.
We report on large spin-filtering effects in epitaxial graphene-based spin valves, strongly enhanced in our specific multilayer case. Our results were obtained by the effective association of chemical vapor deposited (CVD) multilayer graphene with a high quality epitaxial Ni(111) ferromagnetic spin source. We highlight that the Ni(111) spin source electrode crystallinity and metallic state are preserved and stabilized by multilayer graphene CVD growth. Complete nanometric spin valve junctions are fabricated using a local probe indentation process, and spin properties are extracted from the graphene-protected ferromagnetic electrode through the use of a reference AlO/Co spin analyzer. Strikingly, spin-transport measurements in these structures give rise to large negative tunnel magneto-resistance TMR = -160%, pointing to a particularly large spin polarization for the Ni(111)/Gr interface , evaluated up to -98%. We then discuss an emerging physical picture of graphene-ferromagnet systems, sustained both by experimental data and ab initio calculations, intimately combining efficient spin filtering effects arising (i) from the bulk band structure of the graphene layers purifying the extracted spin direction, (ii) from the hybridization effects modulating the amplitude of spin polarized scattering states over the first few graphene layers at the interface, and (iii) from the epitaxial interfacial matching of the graphene layers with the spin-polarized Ni surface selecting well-defined spin polarized channels. Importantly, these main spin selection effects are shown to be either cooperating or competing, explaining why our transport results were not observed before. Overall, this study unveils a path to harness the full potential of low Resitance.Area (RA) graphene interfaces in efficient spin-based devices.
我们报道了外延石墨烯基自旋阀中的大自旋过滤效应，在我们特定的多层结构中这种效应得到了显著增强。我们的结果是通过将化学气相沉积（CVD）多层石墨烯与高质量外延Ni(111)铁磁自旋源有效结合而获得的。我们强调，多层石墨烯CVD生长能够保持并稳定Ni(111)自旋源电极的结晶度和金属态。使用局部探针压痕工艺制备完整的纳米级自旋阀结，并通过使用参考AlO/Co自旋分析仪从石墨烯保护的铁磁电极中提取自旋特性。令人惊讶的是，这些结构中的自旋输运测量产生了大的负隧道磁电阻TMR = -160%，这表明Ni(111)/Gr界面具有特别大的自旋极化，估计高达 -98%。然后，我们讨论了石墨烯 - 铁磁体系统中一种新出现的物理图景，这一图景得到了实验数据和从头算计算的支持，它紧密结合了以下几种产生有效自旋过滤效应的因素：（i）来自石墨烯层的体带结构对提取的自旋方向进行净化；（ii）来自界面处前几层石墨烯上调制自旋极化散射态振幅的杂化效应；（iii）来自石墨烯层与自旋极化Ni表面的外延界面匹配，从而选择明确的自旋极化通道。重要的是，这些主要的自旋选择效应被证明是相互协作或相互竞争的，这解释了为什么我们之前没有观察到这样的输运结果。总体而言，这项研究揭示了一条在高效自旋基器件中充分利用低电阻面积（RA）石墨烯界面全部潜力的途径。
