Kang Min-Gu, Go Gyungchoon, Kim Kyoung-Whan, Choi Jong-Guk, Park Byong-Guk, Lee Kyung-Jin
Department of Materials Science and Engineering, KAIST, Daejeon, 34141, Korea.
Department of Materials Science and Engineering, Korea University, Seoul, 02841, Korea.
Nat Commun. 2020 Jul 17;11(1):3619. doi: 10.1038/s41467-020-17463-3.
Interconversion between charge and spin through spin-orbit coupling lies at the heart of condensed-matter physics. In normal metal/ferromagnet bilayers, a concerted action of the interconversions, the spin Hall effect and its inverse effect of normal metals, results in spin Hall magnetoresistance, whose sign is always positive regardless of the sign of spin Hall conductivity of normal metals. Here we report that the spin Hall magnetoresistance of Ta/NiFe bilayers is negative, necessitating an additional interconversion process. Our theory shows that the interconversion owing to interfacial spin-orbit coupling at normal metal/ferromagnet interfaces can give rise to negative spin Hall magnetoresistance. Given that recent studies found the conversion from charge currents to spin currents at normal metal/ferromagnet interfaces, our work provides a missing proof of its reciprocal spin-current-to-charge-current conversion at same interface. Our result suggests that interfacial spin-orbit coupling effect can dominate over bulk effects, thereby demanding interface engineering for advanced spintronics devices.
通过自旋轨道耦合实现电荷与自旋的相互转换是凝聚态物理的核心内容。在普通金属/铁磁体双层结构中，这种相互转换、自旋霍尔效应及其在普通金属中的逆效应共同作用，导致了自旋霍尔磁电阻，无论普通金属自旋霍尔电导率的符号如何，其符号始终为正。在此，我们报告Ta/NiFe双层结构的自旋霍尔磁电阻为负，这需要一个额外的相互转换过程。我们的理论表明，普通金属/铁磁体界面处的界面自旋轨道耦合引起的相互转换会导致负的自旋霍尔磁电阻。鉴于最近的研究发现了普通金属/铁磁体界面处从电荷电流到自旋电流的转换，我们的工作为同一界面处其反向的自旋电流到电荷电流的转换提供了缺失的证据。我们的结果表明，界面自旋轨道耦合效应可以超过体效应，从而对先进自旋电子器件的界面工程提出了要求。
