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arXiv 1709.04815cond-mat.supr-con
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用于低温存储器的自旋阀约瑟夫森结

Spin-valve Josephson junctions for cryogenic memory

Bethany M. Niedzielski, T. J. Bertus, Joseph A. Glick, R. Loloee, W. P. Pratt,, Norman O. Birge

摘要:

包含两个铁磁层的约瑟夫森结正被考虑用于低温存储器。我们的小组最近证明,通过在反平行和平行配置之间切换两个层的相对磁化方向,可以在零和$π$之间可控地切换这种结与精心选择的层厚度的基态相位差。然而,在这些结可以用于大规模存储器之前,必须解决几个技术问题。这些问题中的许多可以更容易地在单结中研究,而不是在用于相敏测量的超导量子干涉仪(SQUID)中。在这项工作中,我们报告了一个全面的研究自旋阀结含有一个固定的厚度为2.0 nm的Ni层,和NiFe层的厚度在1.1和1.8 nm之间变化的步骤为0.1 nm。我们提取的夫琅和费模式的场位移和临界电流的平行和反平行的磁性状态,以及两个磁性层的开关场。我们还报告了一个类似的结包含一个稍微薄的Ni层的1.6 nm和相同范围的NiFe厚度的部分研究。这些结果代表了绘制相位可控自旋阀约瑟夫森结的"相图”作为两个磁性层厚度的函数的第一步。

英文摘要:

Josephson junctions containing two ferromagnetic layers are being considered for use in cryogenic memory. Our group recently demonstrated that the ground-state phase difference across such a junction with carefully chosen layer thicknesses could be controllably toggled between zero and $π$ by switching the relative magnetization directions of the two layers between the antiparallel and parallel configurations. However, several technological issues must be addressed before those junctions can be used in a large-scale memory. Many of these issues can be more easily studied in single junctions, rather than in the Superconducting QUantum Interference Device (SQUID) used for the phase-sensitive measurements. In this work, we report a comprehensive study of spin-valve junctions containing a Ni layer with a fixed thickness of 2.0 nm, and a NiFe layer of thickness varying between 1.1 and 1.8 nm in steps of 0.1 nm. We extract the field shift of the Fraunhofer patterns and the critical currents of the junctions in the parallel and antiparallel magnetic states, as well as the switching fields of both magnetic layers. We also report a partial study of similar junctions containing a slightly thinner Ni layer of 1.6 nm and the same range of NiFe thicknesses. These results represent the first step toward mapping out a ``phase diagram" for phase-controllable spin-valve Josephson junctions as a function of the two magnetic layer thicknesses.

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