Exchange-coupled magnetic systems are composite magnetic materials consisting of a mixture of magnetically hard and soft phases. By integrating these phases at the nanoscale it is possible to obtain simultaneously the best properties of each phase. A key challenge is to enhance the magnetic properties by improving the regularity of the nanostructure at the 10 nm length scale. This research proposes to achieve this through the development of the self-organized nanochessboard. This novel structure consists of a quasi-periodic tiling of the hard magnetic tetragonal (L10) phase interleaved with a soft magnetic cubic (L12) phase on the nanometer length scale. The nanoschessboard forms by pseudospinodal decomposition around the eutectoid composition in Co-Pt, Fe-Pt and Fe-Pd alloys. The structure features a nanoscale period conducive to strong exchange-coupled magnetism, while the high degree of regularity will enable the development of a deeper understanding of the structure-property relationship, and is expected to enhance the magnetic performance. This investigation will correlate how magnetic properties evolve as the nanochessboard structure is modified by varying the tiling period, the magnetic properties of the individual phases, and the tiling morphology.

NON-TECHNICAL SUMMARY: Magnetic materials underpin several technologies of incredible importance to modern society, including electric motors and digital data storage. There is strong economic motivation to improve the properties of magnetic materials, which could, for example, reduce the weight of a motor or increase the density of data storage. This research will exploit a novel self-organization process to form a composite magnetic material, known as an "exchange-spring magnet", that offers greatly improved magnetic behavior. The new material that will be produced and studied here looks like a chessboard, except that the squares of the chessboard are only nanometers across, and consist of different magnetic materials that closely interact to improve performance. The research is expected to impact the important field of permanent magnet design, where exchange coupling is exploited to obtain maximum energy storage, and will also impact the field of magnetic recording media, where exchange-coupling is used to reduce coercivity in highly anisotropic, nanoscale ordered phases. Beyond the scientific and technological impacts of this research lies a strong commitment by the principal investigator to integrate research and education through the training of graduate students, and the exposure of undergraduate students to the research environment. Furthermore, the principal investigator directs and participates in extensive outreach activities focused on "teaching nano to the public". Magnetism provides a highly visual, appealing approach to learning about nanoscale behavior. These outreach activities target a diverse population, including schools in underserved regions of central Virginia.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Diana Farkas
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University of Virginia
United States
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