Simulations on the gate dependent spin lifetime in graphene non-local spin valve devices
Simulations on the gate dependent spin lifetime in graphene non-local spin valve devices
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石墨烯非局域自旋阀器件中栅极相关自旋寿命的模拟
DOI：
10.1002/pssb.201700293
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
B. Beschoten
中科院分区：
文献类型：
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作者：
M. Drögeler;F. Volmer;C. Stampfer;B. Beschoten
石墨烯非局域自旋阀器件的自旋输运性质通常通过使用一维Bloch-Torrey方程的简化解由Hanle自旋进动测量确定，该方程假设无限长的输运通道和均匀的自旋输运参数。我们研究了有限石墨烯尺寸的影响，并通过有限元模拟探索了空间变化的输运参数对测量的汉勒曲线的影响。我们假设在具有额外费米能级钉扎的接触覆盖的石墨烯区域中增强的自旋退相，并探索未与石墨烯适当解耦的非磁性参考电极的影响。在实验中，通常观察到自旋寿命随着电荷载流子密度的增加而增加。我们的模拟都不能再现这种趋势，表明这种依赖性源于通过未被接触覆盖的石墨烯区域的自旋输运。我们发现，提取的自旋寿命可能被高估的薄片是短于自旋扩散长度。此外，接触诱导的自旋失相导致提取的自旋寿命总体减少。此外，我们表明，非磁性参考电极也可能影响测量的自旋寿命，即使它们不是研究中的传输区域的一部分。
Spin transport properties of graphene non‐local spin valve devices are typically determined from Hanle spin precession measurements by using a simplified solution of the one‐dimensional Bloch‐Torrey equation which assumes infinitely long transport channels and uniform spin transport parameter. We investigate the effects of a finite graphene size and explore the influence of spatially‐varying transport parameters on the measured Hanle curves by finite element simulations. We assume enhanced spin dephasing in the contact‐covered graphene areas with additional Fermi level pinning and explore the influence of non‐magnetic reference electrodes which are not properly decoupled from graphene. In experiments, it is typically observed that the spin lifetime increases with increasing charge carrier density. None of our simulations can reproduce this trend indicating that this dependency originates from spin transport through graphene areas which are not covered by contacts. We find that the extracted spin lifetime might be overestimated in flakes which are shorter than the spin diffusion length. Moreover, contact‐induced spin dephasing leads to an overall reduction of the extracted spin lifetime. Additionally, we show that non‐magnetic reference electrodes may also influence the measured spin lifetime even though they are not part of the transport area under investigation.