Spin dynamics in magnetic nanostructures

摘要 电子的自旋，而不是它的电荷，在电子学中创造了非凡的机会，被称为自旋电子学。这一领域的快速发展要求在理解纳米几何结构中的自旋相互作用方面取得进一步的进展。我们的研究涉及自旋动力学，重点是研究不伴随净电荷的纯自旋流。 A)我们将继续研究用于自旋电子学的非磁性金属层中的自旋电流输运，作为磁源和汇端之间的互连。重点介绍了具有大自旋轨道相互作用、电子自旋关联、高电阻率和电子局域化的重金属薄膜。重金属铂、钽、钨等金属薄膜在自旋电子学中具有重要的应用前景。它们具有非常大的自旋霍尔效应(SHE)和界面自旋轨道扭矩(SOT)，允许人们通过在重金属中使用电流来操作磁随机存取存储器(MRAM)。在确定了铂、钽和钨的自旋输运参数后，我们将研究自旋电流在Au/(铂，钽，钨)界面上的反射。基于我们的PRL 2013，我们期望在Fe/Au/Pd，Pt，Ta，W异质结中观察到量子井态，这是由于Au层中自旋流的空间限制。这是基础物理，因为量子井态是典型的可逆过程，而自旋泵浦是不可逆过程。重金属也将用于自旋扭矩驱动的纳米器件，目的是进一步了解界面SOT和自旋损失记忆的作用，从而使人们能够改进磁随机存取存储器(MRAM)架构。 B)在铁磁/正常金属界面处利用磁矩的大进动角度可以获得大的自旋电流。事实上，利用自旋扭矩装置中的自旋极化净电荷电流，这可以产生类似的自旋电流。YIG薄膜是目前研究最多的产生纯自旋流的材料之一。我们将构建一种基于YIG/Au/Py(PerMaloy)结构的器件，其中Py用作自旋电流探测器。高效、定量的自旋电流探测器的研制是自旋电子学技术的重要组成部分。 C)我们将与E.Girt教授的团队合作开发具有高垂直磁各向异性(PMA)的磁性超晶格，用于高密度磁存储介质和MRAM。有了SFU 4D实验室的新洁净室设施，我们可以制造纳米尺寸的柱子结构，这种结构可以由自旋极化电流驱动，也可以由SHE和SOT驱动。 我们独特的实验研究使我们能够开展广泛的计划，推动基于自旋泵浦、自旋电流输运和自旋扭矩机制的材料和系统的开发，推动工程和基础科学的进步。

Summary The spin of the electron rather than its charge has created remarkable opportunities in electronics, coined spintronics. The rapid progress in this field requires further advances in understanding of spin interactions in nanoscopic geometries. Our studies involve spin dynamics with emphasis on the study of pure spin currents unaccompanied by a net electric charge. a) We are going to continue to study the spin current transport in non-magnetic metallic layers which serve in spintronics, as interconnects between the magnetic source and sink terminals. Particular emphases will be put on heavy metallic thin films which have a large spin orbit interaction, electron spin correlations, and high resistivity with the spatial electron localization. Heavy metal Pt, Ta, and W metallic films are very attractive in spintronics. They have very large Spin Hall Effect (SHE) and interface Spin Orbit Torque (SOT), allowing one to operate Magnetic Random Access Memory (MRAM) by using an electric current in heavy metals. After firmly establishing the spin transport parameters in Pt, Ta, and W, we will study the reflection of spin current at the Au/(Pt,Ta,W) interfaces. We expect, based on our PRL 2013, to observe quantum well states in Fe/Au/Pd,Pt,Ta,W heterostructures due to spatial confinement of spin current in the Au layer. This is fundamental physics because quantum well states are typical to reversible processes while spin pumping is an irreversible process. Heavy metals will be used also in spin torque driven nanopillar devices with the intention to further understand the role of interface SOT and spin loss memory, allowing one to improve Magnetic Random Access Memory (MRAM) architecture. b)Large spin currents can be achieved by using a large angle of precession of the magnetic moment at the ferromagnet/normal metal interface. In fact, this can lead to a comparable spin current using a spin polarized net charge current in spin torque devices. Yttrium Iron Garnet (YIG) films have become one of the most studied materials for generating pure spin currents. We are going to construct a device that is based on YIG/Au/Py(Permaloy) structure, where Py is used as a spin current detector. The development of efficient and quantitative spin current detectors is an important part of spintronic technology. c)We will collaborate with Prof. E. Girt's group in the development of magnetic superlattices with high perpendicular magnetic anisotropy (PMA) for applications directed to high density magnetic memory media and MRAM. With the new clean room facility in SFU's 4D LABS, we can fabricate nanosize pillar structures which can be driven either by spin polarized current or SHE and SOT. Our unique experimental research enables us to carry out a broad program advancing both the engineering and basic science progress in the development of materials and systems based on spin pumping, spin current transport and spin torque mechanism.