Spin Current Phenomena in Non-Collinear Antiferromagnets:From Fundamental Physics to Device Concepts

近年来，反铁磁自旋电子学的研究迅速发展。 然而，到目前为止，大部分的研究都集中在共线反铁磁系统。 在非共线反铁磁系统中的自旋电流现象仍然在很大程度上未被探索。 最近的理论工作揭示了非共线反铁磁体Mn3X中的新现象，其中X是Sn，Ga或Ge。 这些包括一个不寻常的自旋霍尔效应，一个强大的自旋能斯特效应，和反铁磁有序的电操纵。 该计划的核心是及时实验阐明这些现象及其在原型设备中的使用。 这些研究将极大地促进人们对非共线反铁磁体中自旋相关现象的理解，从而推动反铁磁自旋电子学的研究。从技术角度来看，拟议的研究将对磁存储器，自旋扭矩纳米振荡器和自旋波逻辑的未来发展产生重大影响，因此将对未来先进的电子系统产生重大影响。 每年有两名本科生和两名研究生将参与薄膜生长，纳米纤维，电传输和高频测量以及数据分析。将通过科罗拉多州立大学的“物理小商店”和“夏季研究和工程学徒”方案向高中进行推广。 推力我将集中在一个相当不寻常的自旋霍尔效应Mn3Sn。 正常的自旋霍尔效应可以将纵向电荷流转换为横向自旋流，其极化与自旋流方向正交。 与此形成鲜明对比的是，由不寻常的自旋霍尔效应产生的横向自旋流具有沿着自旋流方向的极化。 这种不寻常的现象将通过两种不同的方法来证明。 此外，该效应将用于在具有垂直各向异性的铁磁薄膜中诱导磁化翻转、驱动磁化进动和激发自旋波。 原则上，这些效应都不能用正常自旋霍尔效应、拉什巴效应或拓扑表面态产生的自旋电流来实现。 推力II将集中在自旋能斯特效应，其中一个使用热梯度产生纯自旋电流的过程。 最近的实验已经揭示了这种效果在Pt。 最近的理论研究表明，这种效应也可以发生在Mn3X中，并且可以明显强于Pt。 推力II将阐明Mn3X薄膜的这些预测的强自旋能斯特效应。 它也计划使用这种效应的自旋轨道转矩感应磁化翻转铁磁薄膜垂直各向异性。 推力III将专注于Mn3X中反铁磁有序的控制。 工作计划操纵反铁磁状态使用阻尼类和类场自旋轨道扭矩和移动域壁通过自旋转移扭矩。虽然理论表明这种有序控制是可行的，但这还没有得到实验证明。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Recent years have witnessed a rapidly growing interest in antiferromagnetic spintronics. Up to now, however, most of the research has focused on collinear antiferromagnetic systems. Spin current phenomena in non-collinear antiferromagnetic systems remain largely unexplored. Very recent theoretical work has uncovered new phenomena in non-collinear antiferromagnets Mn3X, where X is Sn, Ga, or Ge. These include an unusual spin Hall effect, a strong spin Nernst effect, and electric manipulation of antiferromagnetic ordering. The heart of this program is the timely experimental elucidation of these phenomena and their use in prototype devices. The studies will largely promote the understanding of spin-related phenomena in non-colinear antiferromagnets and will thereby significantly advance the research field of antiferromagnetic spintronics. From a technological perspective, the proposed research will have significant implications for the future development of magnetic memory, spin-torque nano-oscillators, and spin-wave logic and will therefore have a major impact on future advanced electronic systems. Two undergraduate students and two graduate students per year will participate in film growth, nanofabrication, electrical transport and high-frequency measurements, and data analysis. Outreach to high schools will be accomplished through the Colorado State University 'Little Shop of Physics' and the 'summer Research and Engineering Apprenticeship" Programs.The program consists of three main research thrusts. Thrust I will focus on a rather unusual spin Hall effect in Mn3Sn. A normal spin Hall effect can convert a longitudinal charge current to a transverse spin current whose polarization is orthogonal to the spin flow direction. In stark contrast, the transverse spin current produced by the unusual spin Hall effect has a polarization that is along the spin flow direction. This unusual phenomenon will be demonstrated through two distinct approaches. Further, the effect will be used to induce magnetization switching, drive magnetization precession, and excite spin waves in ferromagnetic thin films with perpendicular anisotropy. None of these effects can be achieved, in principle, with spin currents produced by the normal spin Hall effect, the Rashba effect, or topological surface states. Thrust II will focus on the spin Nernst effect, a process in which one uses a thermal gradient to produce pure spin currents. Recent experiments have revealed this effect in Pt. Very recent theoretical work indicates that the effect can also occur in Mn3X and can be significantly stronger than in Pt. Thrust II will elucidate these predicted strong spin Nernst effect for Mn3X films. It is also planned to use this effect for spin-orbit torque-induced magnetization switching in ferromagnetic films with perpendicular anisotropy. Thrust III will focus on the control of antiferromagnetic ordering in Mn3X. Work is planned to manipulate antiferromagnetic states using damping-like and field-like spin-orbit torques and move domain walls through spin transfer torque. While theory suggests that such ordering control is feasible, this has not yet been demonstrated experimentally.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.