RUI: Collaborative Research: Spin-gapless semiconductivity and half-metallicity in Heusler alloys

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Non-Technical Abstract:Current computing technology is based on the manipulation of the charge of electrons for the purpose of information processing. Hard disks, which are used in large-scale storage of data, function by exploiting the intrinsic magnetism of electrons. Spintronics is a fledging field that unites these two technologies to create a new computing paradigm that could result in substantial enhancements in computing speed and attendant energy efficiency. Spintronic devices such as magnetic random access memory (MRAM) have already been commercialized but the potential of spintronics is far greater. This project advances the field of spintronics through the systematic discovery of new materials that possess the necessary electronic and magnetic properties to undergird large-scale development of new spintronic devices. The project combines both theoretical and experimental approaches to maximize the effectiveness of the discovery process. In addition to its direct scientific impact, the project positively influences the development of the future science and technology workforce through the heavy involvement of undergraduate students in all aspects of the research. Outreach programs involving K-12 students and the general public further broadens the impact of the project via engaging activities that emphasize and elevate the importance of science to the well-being of humanity. This project is jointly funded by the Division of Materials Research (DMR) and the Established Program to Stimulate Competitive Research (EPSCoR).Technical Abstract:The main goal of this project is the identification and synthesis of new half-metallic (HM) and spin-gapless semiconducting (SGS) materials for applications in spintronics. In particular, this project investigates structural, magnetic, electronic, and spin-transport properties of HM and SGS Heusler alloys in bulk and thin-film geometry. This is achieved by performing comprehensive theoretical and experimental investigations of candidate materials, using state-of-the-art techniques, tools, and research methods, including X-ray diffraction, transmission electron microscopy, Quantum Design VersaLab magnetometer, Quantum Design Physical Property Measurement System, point-contact Andreev reflection, and first-principles density functional calculations. The project is motivated by recent discovery that certain Heusler compounds change their ground state from metallic to SGS and/or HM upon modification of their elemental compositions. This approach has a clear advantage over mechanical strain-induced half-metallic transitions reported in the literature, as it requires no external pressure. Second, this project provides experimental confirmation that certain half-metals retain a 100% spin-polarization in thin-film geometry, contrary to the conventional wisdom that reduced geometry destroys half-metallicity due to the emergence of surface states. This could open a new page in spintronic applications, e.g., in devices based on multilayer design, such as magnetoresistive tunnel junctions. This project is jointly funded by the Division of Materials Research (DMR) and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.