Novel nanomagnetic structures, materials and devices

利用新型薄膜材料和纳米结构可以应对信息技术和替代能源领域的重大挑战和机遇。这项提议的背景分为以下几个领域：自旋电子学；磁农学；磁记录(硬盘驱动器[HDs])；以及光伏。与传统的基于电荷的电子设备相比，基于Spin的设备提供了许多机会和优势。随着器件密度的增加，总能量消耗增加，这是当前电子体系结构中的一个相当大的障碍。除了焦耳加热，电迁移和电容耦合的影响也是主要问题。基于自旋的设备通过使用纯自旋电流而不是净电荷流来处理和传输信息，从而克服了这些问题。用磁性手段存储的信息本质上也是非易失性的。另一种传输信息的方式是通过自旋波。我的研究将探索一个新的方向--磁晶。这些是由偶极力耦合的磁性纳米结构阵列，其中自旋波色散的能带结构工程允许自旋波的受控传播。受光子带隙材料的启发，这是一个非常有前途的自旋电子学新方向。在磁记录领域(30多年来存储信息的主要方式)，人们正在寻找新的复合材料、结构和磁化反转方案，目标是创造热稳定的磁化并在不断降低的维度上操纵它。为了提高HD的记录密度，必须减小记录介质中的磁性颗粒的直径。这需要使用有序的3D-4D、3D-5D和3D-4F化合物，它们具有比当前介质中使用的无序的HCP COPT大得多的磁各向异性值。我们正在与记录行业合作解决两个主要挑战：1)需要在400°C以上进行有序磁性化合物的制造(当前介质是在常温下制造的)；以及2)沿颗粒生长方向的非均匀磁化反转的设计，以促进具有如此大的磁各向异性的颗粒的磁化反转。我们是SFU旨在开发用于光伏应用的新型材料的大型研究工作的一部分。其中一个目标是开发低成本、高效率的太阳能电池。II-VI族化合物半导体，特别是四元系CZTS(铜、锡、锌硫化物)化合物，由于含有丰富的低成本材料而备受关注。与二元和三元半导体相比，四元化合物在材料性质上具有更大的灵活性，但同时，它们具有大量的本征晶格缺陷，这显著恶化了它们的光伏性能。我们计划沿不同的晶向生长CZTS单晶薄膜，并研究生长对CZTS薄膜的缺陷密度、第二相的存在和电学性质的影响。一个长期目标是探索如何利用SFU广泛的III-V设施将III-V和II-VI半导体集成到多结太阳能电池中。太阳能电池研究对于让加拿大工业在该领域处于世界领先地位至关重要。开发这项技术可以显著减少加拿大的温室气体排放，减缓全球变暖，并展示加拿大在环境保护方面的领导地位。

Important challenges and opportunities in information technology and alternative energy can be addressed using novel thin film materials and nanostructures. The context for this proposal falls into the following areas: spintronics; magnonics; magnetic recording (hard drives [HDs]); and photovoltaics.Spin-based devices present a number of opportunities and advantages compared to conventional charge-based electronics. As device density is increased, overall energy dissipation increases, which is a considerable obstacle in current electronic architecture. As well as Joule heating, the effects of electromigration and capacitive coupling are also major concerns. Spin-based devices overcome these problems by processing and transporting information using pure spin currents, without net charge flow. Information stored by magnetic means is also inherently non-volatile.Another way of transferring information is via spin waves. My research will explore a new direction – magnonic crystals. These are arrays of magnetic nanostructures, coupled by dipolar forces, in which band-structure engineering of the spin wave dispersion allows for the controlled propagation of spin waves. Inspired by photonic band-gap materials, this is a very promising new direction in spintronics.In the area of magnetic recording (the main way of storing information for more than 30 years), there is a search for new composite materials, structures, and magnetization reversal schemes, with the goal of creating thermally stable magnetization and manipulating it at ever-decreasing dimensions. To increase the recording density of HDs, the diameter of magnetic grains in recording media has to be reduced. This requires the use of ordered 3d-4d, 3d-5d, and 3d-4f compounds, which have much larger magnetic anisotropy values than the disordered hcp CoPt, used in current media. There are two main challenges that we are addressing in collaboration with the recording industry: 1) fabrication of ordered magnetic compounds that needs to be carried out above 400°C (current media are fabricated at ambient temperature); and 2) the design of a nonuniform magnetization reversal along the direction of the grain growth to facilitate the magnetization reversal in grains with such large magnetic anisotropy.We are part of the large research effort at SFU aiming to develop novel materials for photovoltaic applications. One goal is to develop low cost, high efficiency solar cells. II-VI compound semiconductors, in particular quaternary CZTS (copper tin zinc sulfide) compounds, have drawn considerable attention because they consist of abundant, low-cost materials. The quaternary compounds have increased flexibility in material properties, relative to binary and ternary semiconductors, but at the same, they have a large variety of intrinsic lattice defects, which significantly deteriorate their photovoltaic performance. We plan to grow single crystal CZTS films along different crystallographic orientations and investigate the effect of growth on the defect density, the presence of secondary phases, and the electrical properties of CZTS films. A long term objective is to explore ways to integrate III-V and II-VI semiconductors into multijunction solar cells using the extensive III-V facilities at SFU. Solar cell research is vital to making Canadian industry world leaders in the field. Developing this technology could significantly reduce Canada’s greenhouse emissions, slow global warming, and demonstrate Canadian leadership with regards to environmental protection.