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Abstract Non-volatile phase-change memory devices utilize local heating to toggle between crystalline and amorphous states with distinct electrical properties. Expanding on this kind of switching to two topologically distinct phases requires controlled non-volatile switching between two crystalline phases with distinct symmetries. Here, we report the observation of reversible and non-volatile switching between two stable and closely related crystal structures, with remarkably distinct electronic structures, in the near-room-temperature van der Waals ferromagnet Fe5−δGeTe2. We show that the switching is enabled by the ordering and disordering of Fe site vacancies that results in distinct crystalline symmetries of the two phases, which can be controlled by a thermal annealing and quenching method. The two phases are distinguished by the presence of topological nodal lines due to the preserved global inversion symmetry in the site-disordered phase, flat bands resulting from quantum destructive interference on a bipartite lattice, and broken inversion symmetry in the site-ordered phase.
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Mechanical Properties of an Ultrahard In Situ Amorphous Steel Matrix Composite
We report compression tests on micropillars manufactured from bulk specimens of partially devitrified SAM2×5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4). Yield strength values of ≈6 GPa are obtained. Such a high strength can be attributed to the higher glass transition temperature (883 K) of this material, which impedes the multiplication of shear bands under loading, and to the presence of hard crystalline domains that result from devitrification of the amorphous powders during powder consolidation. The Vickers hardness of the specimens is found to be strongly correlated to the processing temperature and, hence to the volume of crystalline phases present in the specimens. As the processing temperature is increased, there is a reduction in free volume from the structural relaxation process in the amorphous alloy, leading to the eventual nucleation of crystalline phases of BCC Fe, Cr2B, Cr21.30Fe1.7C6, or Fe23B2C4, during the densification process. These results shed light on the relationship between nanocrystalline domains and the mechanical behavior of Fe‐based amorphous/crystalline composites.
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- Award ID(s):
- 1911372
- PAR ID:
- 10639967
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Engineering Materials
- Volume:
- 26
- Issue:
- 11
- ISSN:
- 1438-1656
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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