Novel nanomagnetic structures, materials and devices

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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.