Novel nanomagnetic structures, materials and devices

利用新型薄膜材料和纳米结构可以解决信息技术和替代能源方面的重大挑战和机遇。本提案的背景分为以下几个方面：自旋电子学；magnonics;磁记录（硬盘驱动器[HDs]）；和光伏发电。与传统的基于电荷的电子设备相比，基于自旋的设备提供了许多机会和优势。随着器件密度的增加，总能量耗散增加，这是当前电子结构中一个相当大的障碍。除了焦耳加热外，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来处理和传输信息，而无需净电荷流，从而克服了这些问题。通过磁性手段存储的信息也具有固有的非易失性。另一种传递信息的方式是通过自旋波。我的研究将探索一个新的方向——磁晶体。这些是磁性纳米结构阵列，由偶极力耦合，其中自旋波色散的带结构工程允许自旋波的可控传播。受光子带隙材料的启发，这是自旋电子学中一个非常有前途的新方向。在磁记录（30多年来存储信息的主要方式）领域，人们正在寻找新的复合材料、结构和磁化反转方案，其目标是创造热稳定的磁化并在不断减小的维度上操纵它。为了提高硬盘的记录密度，必须减小记录介质中磁性颗粒的直径。这需要使用有序的3d-4d、3d-5d和3d-4f化合物，它们的磁各向异性值比目前介质中使用的无序的hcp CoPt大得多。我们正在与唱片行业合作解决两个主要挑战：1)制造需要在400°C以上进行的有序磁性化合物（目前的介质是在环境温度下制造的）；2)设计沿晶粒生长方向的非均匀磁化反转，以促进磁性各向异性较大的晶粒的磁化反转。我们是SFU旨在开发光伏应用新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化合物半导体，特别是季型CZTS（铜锡硫化锌）化合物，由于其包含丰富的低成本材料而引起了相当大的关注。相对于二元和三元半导体，四元化合物在材料性能上具有更高的灵活性，但同时，它们具有大量的本征晶格缺陷，这大大降低了它们的光伏性能。我们计划沿着不同的晶体取向生长单晶CZTS薄膜，并研究生长对CZTS薄膜缺陷密度、二次相存在和电学性能的影响。长期目标是探索利用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的方法。太阳能电池的研究对于使加拿大成为该领域的世界领导者至关重要。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.