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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Understanding and Tuning Magnetism in Layered Ising‐Type Antiferromagnet FePSe 3 for Potential 2D Magnet

Abstract Recent developments in 2D magnetic materials have motivated the search for new van der Waals magnetic materials, especially Ising‐type magnets with strong magnetic anisotropy. Fe‐based M P X 3 ( M = transition metal, X = chalcogen) compounds such as FePS 3 and FePSe 3 both exhibit an Ising‐type magnetic order, but FePSe 3 receives much less attention compared to FePS 3 . This work focuses on establishing the strategy to engineer magnetic anisotropy and exchange interactions in this less‐explored compound. Through chalcogen and metal substitutions, the magnetic anisotropy is found to be immune against S substitution for Se whereas tunable only with heavy Mn substitution for Fe. In particular, Mn substitution leads to a continuous rotation of magnetic moments from the out‐of‐plane direction toward the in‐plane. Furthermore, the magnetic ordering temperature displays non‐monotonic doping dependence for both chalcogen and metal substitutions but due to different mechanisms. These findings provide deeper insight into the Ising‐type magnetism in this important van der Waals material, shedding light on the study of other Ising‐type magnetic systems as well as discovering novel 2D magnets for potential applications in spintronics.

2D magnet↗
DOE OSTI2017

Ferromagnetic–Antiferromagnetic Coupling by Distortion of Fe/Mn Oxygen Octahedrons in (BiFeO 3 ) m (La 0.7 Sr 0.3 MnO 3 ) n Superlattices

Interface enhanced magnetism attracts much attention due to its potential use in exploring novel structure devices. Nevertheless, the magnetic behavior at interfaces has not been quantitatively determined. In this study, abnormal magnetic moment reduction is observed in La 0.7 Sr 0.3 MnO 3 (LSMO)/BiFeO 3 (BFO) superlattices, which is induced by ferromagnetic (FM)/antiferromagnetic (AFM) coupling in the interface. With reduced repetition of the superlattice's unit cell [(LSMO) n /(BFO) n ] 60/ n ( n = 1, 2, 5, 10) on a SrTiO 3 substrate, magnetic moment reduction from 25.5 emu cc −1 ([(LSMO) 10 /(BFO) 10 ] 6 ) to 1.5 emu cc −1 ([(LSMO) 1 /(BFO) 1 ] 60 ) is obtained. Ab initio simulations show that due to the different magnetic domain formation energies, the magnetic moment orientation tends to be paramagnetic in the FM/AFM interface. The work focuses on the magnetic domain formation energy and provides a pathway to construct artificial heterostructures that can be an effective way to tune the magnetic moment orientation and control the magnetization of ultrathin films.

Xiong, Jie↗
DOE OSTI2017

CaCoSO diluted magnetic antiferromagnet semiconductor as efficient thermoelectric materials

Highlights: • CaCoSO exhibit direct (Γ{sup v}- Γ{sup c}) gap of about 2.187 eV for spin-up (↑). • CaCoSO exhibit direct (K{sup v}-K{sup c}) gap of about 1.187 eV for spin-down(↓). • An indirect gap (Γ{sup v}-K{sup c}) of about 0.4 eV for the spin-polarized CaCoSO. • Small gap turn CaCoSO to be as promising candidate for thermoelectric materials. - Abstract: We have reported the thermoelectric properties of the recently synthesized CaCoSO single crystal by Salter et al. in 2016. It is quite interesting to mention that CaCoSO single crystals exhibit a direct energy gap (Γ{sup v}- Γ{sup c}) of about 2.187 eV for the spin-up (↑) channel, which turns out to be a (K{sup v}-K{sup c}) direct gap of about 1.187 eV for the spin-down (↓) channel, resulting in an indirect gap (Γ{sup v}-K{sup c}) of about 0.4 eV for the spin-polarized CaCoSO single crystal. Such a small gap makes CaCoSO a promising candidate for thermoelectric materials. Calculations reveal a remarkable finding that the CaCoSO single crystal exhibits high electrical conductivity, low thermal conductivity and a large Seebeck coefficient; therefore, based on these findings, the CaCoSO single crystal may be considered an efficient thermoelectric material. The electron clouds of CaO{sub 3}S{sub 4} and CoS{sub 3}O exhibit a planar shape with conjugated electron orbitals and exhibit a strong covalent Ca−O, Co−O bonding. This is another factor which makes CaCoSO a promising candidate for thermoelectric materials, since covalent bonding is more favorable for the transport of the carriers than ionic bonding. CaO{sub 3}S{sub 4} and CoS{sub 3}O are the main sources for the thermoelectric generator in CaCoSO. Therefore, based on the above findings, we can conclude that CaCoSO could be a promising thermoelectric material.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Scanning tunneling microscopy study of the antiferromagnetic topological insulator MnBi 2 Se 4

Topological insulators with intrinsic magnetic ordering such as MnBi 2 Se 4 have been predicted to host many exotic topological phenomena including dissipationless edge states and magnetoelectric effects. Here we use scanning tunneling microscopy to study the surface of MnBi 2 Se 4 epitaxial thin films. Large scale topographic images show steps between van der Waals layers and screw dislocations. While we find the Se-termination predominant on the surface, areas attributed to Bi-termination are found at the edges of small islands in as-grown films, or in larger areas upon removal of surface capping. Here, we compare these terminations through an analysis of step heights, atomic resolution images and tunneling spectroscopy. Tunneling spectra on the Se-termination reveals semiconducting behavior, with an apparent bandgap of >0.18eV that depends on the tip height. In contrast, tunneling spectra of the Bi-termination appears gapless, which could be an indication of dangling bond states on the surface. In both cases, a hexagonal 3.9Å lattice is observed that is consistent with the expected crystal structure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗