Spintronics with Yttrium Iron Garnets - From Fundamental Physics to Device Concepts

摘要：最近的研究表明，人们可以在钇铁石榴石薄膜内外传输自旋电流，并利用这种薄膜产生自旋电流。这为钇铁石榴石基自旋电子学开辟了一个新的研究领域。这个新项目将解决这一新兴领域的四个问题：(1)钇铁石榴石/正常金属界面的自旋泵浦；(2)界面自旋散射控制钇铁石榴石薄膜弛豫及其器件应用；(3)界面自旋散射的自旋波放大及其潜在的器件应用；(4)自旋塞贝克效应及其潜在的器件应用。主题(1)讨论了钇铁石榴石/普通金属界面上自旋角动量传递的效率。课题(2)和(3)考虑了自旋极化电子在钇铁石榴石薄膜表面的散射，研究了这种界面自旋散射对薄膜内均匀模式和非均匀模式的影响，并利用界面自旋散射和钇铁石榴石薄膜展示了一种新型的自旋力矩振荡器以及低损耗延迟线和移相器。Topic(4)研究了垂直构型钇铁石榴石薄膜中的自旋塞贝克效应，其中温度梯度垂直于薄膜平面和磁化强度。在Topic(4)中，还计划展示一种新的依赖于热诱导界面角动量传递的自旋力矩振荡器。虽然将展示几个设备概念，但新计划不包括自旋电子设备的实施和集成计划，因此工作量是合理的。这项新计划得到了自旋电子学三个主要小组的初步工作和合作的支持。教育活动包括在高等固体物理课程中教授自旋电子学。智力优势：(1)该计划将产生基础物理学的第一个结果(i)在钇铁石榴石/正常金属界面上的自旋角动量传递，（ii）正常金属层中自旋电流与钇铁石榴石薄膜中激发之间的相互作用，以及（iii）通过热诱导角动量传递的弛缓控制。(2)该程序将演示磁绝缘体弛豫控制的新方法。这种控制是非常理想的，因为磁化弛豫不仅在自旋基器件的动力学中起着关键作用，而且对器件的响应时间也有一个自然的限制。(3)将展示两种新型自旋转矩振荡器。(4)该计划将产生自旋波放大的新方法，从而为一类新的自旋波设备打开大门。更广泛的影响：该计划将触及几个基本问题，因此将对钇铁石榴石自旋电子学的新研究领域的进步产生重大影响。钇铁石榴石自旋电子器件的技术意义源于钇铁石榴石的两个特点：(1)极小的阻尼和(2)电绝缘性能。例如，与铁磁金属基振荡器相比，小阻尼将允许开发新的自旋扭矩振荡器，这些振荡器具有更窄的谱线宽度和更大的信噪比。自旋波阻尼是制约自旋波微波器件和逻辑器件发展的瓶颈。自旋波放大的新方法将促进这些器件的发展。该项目将为研究生、本科生和高中生提供研究机会。科罗拉多州的高中将通过科罗拉多州立大学的物理小店项目来完成。该计划的结果将通过会议报告、出版物以及对国家实验室和工业的访问广泛传播。

Abstract: Recent work demonstrates that one can transmit spin currents into and out of yttrium iron garnet thin films, as well as use such films to generate spin currents. This demonstration opens a new research field of yttrium iron garnet-based spintronics. This new program will address four issues in this emerging field: (1) spin pumping at yttrium iron garnet/normal metal interfaces; (2) relaxation control in yttrium iron garnet films through interfacial spin scattering and its device applications; (3) spin-wave amplification through interfacial spin scattering and potential device applications; and (4) spin Seebeck effects and potential device applications. Topic (1) addresses the efficiency of spin angular momentum transfer across yttrium iron garnet/normal metal interfaces. Topics (2) and (3) consider the scattering of spin-polarized electrons off the surface of a yttrium iron garnet film and study the effects of such interfacial spin scattering on both uniform and non-uniform modes in the film, and make use of the interfacial spin scattering and yttrium iron garnet thin films to demonstrate a new type of spin torque oscillator as well as low-loss delay lines and phase shifters. Topic (4) studies the spin Seebeck effect in yttrium iron garnet films in a perpendicular configuration in which the temperature gradient is perpendicular to both the film plane and the magnetization. Under Topic (4), work is also planned to demonstrate a new spin torque oscillator that relies on thermally induced interfacial angular momentum transfer. Although several device concepts will be demonstrated, the new program does not include plans for the implementation and integration of spintronic devices such that the workload is reasonable. The new program is supported by preliminary work and collaborations with three leading groups in spintronics. Education activities include teaching spintronics in Advanced Solid State Physics course.Intellectual Merits: (1) This program will yield the first results on fundamental physics underlying (i) spin angular momentum transfer across yttrium iron garnet/normal metal interfaces, (ii) interactions between spin currents in normal metal layers and excitations in yttrium iron garnet films, and (iii) relaxation control through thermally induced angular momentum transfer. (2) The program will demonstrate new methods for relaxation control in magnetic insulators. Such control is highly desirable because magnetization relaxation not only plays a critical role in the dynamics of spin-based devices but also sets a natural limit to the response time of a device. (3) Two new types of spin torque oscillators will be demonstrated. (4) The program will yield novel approaches for spin-wave amplifications and thereby opens the door to a new class of spin-wave devices. Broader Impacts: The program will touch on several fundamental issues and will therefore have a significant impact on the advancement of the new research field of yttrium iron garnet spintronics. The technological significance of yttrium iron garnet spintronic devices originates from two features of yttrium iron garnets: (1) extremely small damping and (2) electrically insulating property. The small damping, for example, will allow for the development of new spin torque oscillators that exhibit much narrower spectral linewidth and much larger signal-to-noise ratios than ferromagnetic metal-based oscillators. The advancement of spin wave-based microwave devices and logic devices is bottlenecked by spin-wave damping. The new approaches for spin-wave amplification will promote the development of these devices. The program will provide research opportunities for graduate, undergraduate, and high school students. Outreach to high schools in Colorado will be accomplished through the Colorado State University Little Shop of Physics program. The results from this program will be disseminated broadly through conference presentations, publications, and visits to national laboratories and industry.