| NSF Org: |
DMR Division Of Materials Research |
| Recipient: |
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| Initial Amendment Date: | August 10, 2012 |
| Latest Amendment Date: | August 10, 2012 |
| Award Number: | 1235230 |
| Award Instrument: | Standard Grant |
| Program Manager: |
John Schlueter
jschluet@nsf.gov (703)292-7766 DMR Division Of Materials Research MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | September 1, 2012 |
| End Date: | August 31, 2017 (Estimated) |
| Total Intended Award Amount: | $264,505.00 |
| Total Awarded Amount to Date: | $264,505.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1001 EMMET ST N CHARLOTTESVILLE VA US 22903-4833 (434)924-4270 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
P. O. Box 400195 Charlottesville VA US 22904-4195 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | DMR SHORT TERM SUPPORT |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.049 |
ABSTRACT
****Technical Abstract****
First-principles theory (DFT and beyond) will be used to screen thousands of half-metals and choose a set of experimentally-accessible starting materials. We will also develop models based on state-of-the-art Non-Equilibrium Green Functions to calculate their transport characteristics. Experimentally, we will synthesize the candidate materials, test their electrical, magnetic, and structural characteristics and compare to theoretical predictions. The results of this characterization will then be fed back to refine our theoretical methods. Promising materials will be tested with more advanced techniques (such as spin-polarized tunneling and local-electrode atom probe tomography), providing more detailed information for more advanced modeling. The most promising materials will be used in prototype TMR and (CIP/CPP)-GMR devices. A specific disruptive technology goal is the design, fabrication and demonstration of a low moment half-metal with perpendicular anisotropy and low magnetic damping ideally suited for STT-RAM. This will be accomplished through the tight circular work flow among rational design, computational verification, spin transport modeling, experimental characterization and device fabrication. Several interdisciplinary courses at UA and UVa will be developed to quickly incorporate lessons we have learned into the classroom and provide students with cutting-edge training. Software developed in the project will be deployed on the NSF NanoHUB.
****Non-Technical Abstract****
In today's electronic devices electrons are manipulated through their electrical charge. However, electrons have another property called "spin". Electrons behave as if they were spinning about an axis. According to quantum mechanics the spin axis of an electron can point in only one of two directions, i.e. either "up" or "down". In most materials there are equal numbers of up and down electrons and usually both types respond to an electric field in the same way. In magnetic materials, however, the number of up and down spin electrons may be different and the two types of electrons may respond to electric fields in different ways. The most extreme example of this phenomenon is a "half-metal" - meaning that one set of electrons is a metal and the other set is an insulator. A specific technology goal is the design, fabrication and demonstration of a half-metal with carefully controlled magnetic properties tailored to meet the requirements of non-volatile magnetic memories (which aim to replace traditional RAM). We aim to provide an improved understanding of half-metals and magnetic materials in general, in particular how one can relate 'first-principles' calculations to experimentally accessible and technologically relevant materials and device parameters. This project will help to increase the STEM workforce by providing research experiences for undergraduates and high school students and will enhance its diversity through its composition and collaboration with HBCU faculty. Several interdisciplinary courses at UA and UVa will be developed to quickly incorporate lessons learned into the classroom and provide students with cutting-edge training.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Using high-performance computing and first principles Density Functional Theory (DFT), the UVA-UA collaborative team scanned through 1359 Heusler family compounds consisting of 576 “full” Heuslers (X2YZ), 378 “half” Heuslers (XYZ) and 405 “inverse” Heuslers (XYXZ), to identify potential Slater-Pauling semiconductors and half metals with 100% spin polarization, and create an open public Heusler database. Significantly, we explored the stability of these phases relative to possible competing phases, that are now included in the OQMD database of calculated alloy phases.
We predicted 5 unreported semiconducting half-Heuslers, 4 unreported near half-metallic inverse-Heuslers 5 unreported half-metallic full-Heuslers and two layered Heusler systems have low hull distances close to be 0 as synthesizable compounds. Among them, several candidate compounds were sent to our experimental collaborators to fabricate these novel ternary phase Slater-Pauling semiconductors and half-metals.
In addition, we explored 39 Heusler/MgO[001] as well as 21 layered all-Heusler superlattice structures with layering in [001], [110] directions, as well as 8 layered Heusler superlattices with layering in [111] direction, to see if we can keep half-metallicity while getting perpendicular anisotropy and high TMR I-V ratio at the same time. These candidate materials are suitable materials for magnetic tunnel junctions (MTJs).
Many interesting materials were predicted to be stable half-metals, many of which were predicted for the first time. Details are described in the report.
Two layered Heusler systems, Fe1.5TiSb and Co1.5TiSn , two inverse-Heusler compound, Mn2CoGa and Mn2FeSi, and one full Heusler compound, Fe2MnGe, were predicted by DFT as synthesizable Slater-Pauling materials, that have been investigated in experiments. The experimental group has successully fabricated cubic Fe1.5TiSb compound as a novel Slater-Pualing semiconductor and Co1.5TiSn compound as a novel Slater-Pauling half-metal. The inverse-Heusler Mn2CoGa has been successfully fabricated as cubic near half-metal with high Curie temperature, and Mn2FeSi was also fabricated as cubic antiferromagnet. Although Fe2MnGe were predicted to be a novel cubic Slater-Pauling half-metal, the experimental group found a new hexgonal phase of this compound with high saturation magnetization, crystalline anisotropy and possible half-metallicity. Those compounds can be good candidate materials for future spintronic applications.
Broader Impact: Material from the project including discovered new materials were included in various databases. Results from the projects were presented at numerous conferences and included in several publications. Material was also included and taught in parts of the course "Fundamentals of Nanoelectronics" for UG and grad students at UVA.
Last Modified: 12/16/2017
Modified by: Avik Ghosh
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