Magnetoresistance of vertical Co-graphene-NiFe junctions controlled by charge transfer and proximity-induced spin splitting in graphene
Magnetoresistance of vertical Co-graphene-NiFe junctions controlled by charge transfer and proximity-induced spin splitting in graphene
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DOI：
10.1088/2053-1583/aa7452
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发表时间：
2017-09-01
期刊：
影响因子：
5.5
通讯作者：
Grigorieva, I. V.
中科院分区：
文献类型：
--
作者：
Asshoff, P. U.;Sambricio, J. L.;Grigorieva, I. V.
石墨烯被誉为自旋电子学的理想材料，这是由于弱的内在自旋轨道相互作用，这有助于横向自旋输运和其电子性质的可调谐性，包括在石墨烯中诱导磁性的可能性。石墨烯的另一个有前景的应用涉及其在垂直磁阻器件中用作分隔铁磁金属（FM）的间隔物，垂直磁阻器件是广泛用作磁传感器的最突出的一类自旋电子器件。特别是，少层石墨烯被预测为完美的自旋过滤器。在这里，我们表明，石墨烯在这样的设备中的作用（至少在石墨烯和FM之间的外延对齐的情况下）是不同的，并确定由邻近诱导的自旋分裂和电荷转移与相邻的铁磁金属，使石墨烯弱FM电极，而不是自旋过滤器。为此，我们报告了在垂直Co-石墨烯-NiFe结中观察到的磁阻（MR），其中1-4个石墨烯层将铁磁体分开，并证明了MR符号对层数的依赖性及其在相对较小的偏置电压下的反转与弱掺杂和不同自旋极化的石墨烯层之间的自旋输运一致。所提出的解释支持的MR符号反转的观察偏置的Co-石墨烯-BN-NiFe设备和全面的结构表征。我们的研究结果提出了一种新的架构与电控MR垂直设备。
Graphene is hailed as an ideal material for spintronics due to weak intrinsic spin-orbit interaction that facilitates lateral spin transport and tunability of its electronic properties, including a possibility to induce magnetism in graphene. Another promising application of graphene is related to its use as a spacer separating ferromagnetic metals (FMs) in vertical magnetoresistive devices, the most prominent class of spintronic devices widely used as magnetic sensors. In particular, few-layer graphene was predicted to act as a perfect spin filter. Here we show that the role of graphene in such devices (at least in the absence of epitaxial alignment between graphene and the FMs) is different and determined by proximity-induced spin splitting and charge transfer with adjacent ferromagnetic metals, making graphene a weak FM electrode rather than a spin filter. To this end, we report observations of magnetoresistance (MR) in vertical Co-graphene-NiFe junctions with 1-4 graphene layers separating the ferromagnets, and demonstrate that the dependence of the MR sign on the number of layers and its inversion at relatively small bias voltages is consistent with spin transport between weakly doped and differently spin-polarized layers of graphene. The proposed interpretation is supported by the observation of an MR sign reversal in biased Co-grapheneh-BN-NiFe devices and by comprehensive structural characterization. Our results suggest a new architecture for vertical devices with electrically controlled MR.