Search NASA⌕ Search

SEARCH · Search NASA

Results for “antiferromagnetic materials”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Interplay between Local Moment and Itinerant Magnetism in the Layered Metallic Antiferromagnet TaFe 1.14 Te 3

Two-dimensional antiferromagnets have garnered considerable interest for the next generation of functional spintronics. However, many bulk materials from which two-dimensional antiferromagnets are isolated are limited by their air sensitivity, low ordering temperatures, and insulating transport properties. TaFe 1+y Te 3 aims to address these challenges with increased air stability, metallic transport, and robust antiferromagnetism. Here, we synthesize TaFe 1+y Te 3 (y = 0.14), identify its structural, magnetic, and electronic properties, and elucidate the relationships between them. Axial-dependent high-field magnetization measurements on TaFe 1.14 Te 3 reveal saturation magnetic fields ranging between 27-30 T with saturation magnetic moments of 2.05- 2.12 μ B . Magnetotransport measurements confirm TaFe 1.14 Te 3 is metallic with strong coupling between magnetic order and electronic transport. Angle-resolved photoemission spectroscopy measurements across the magnetic transition uncover a complex interplay between itinerant electrons and local magnetic moments that drives the magnetic transition. In conclusion, we demonstrate the ability to isolate few-layer sheets of TaFe 1.14 Te 3 , establishing TaFe 1.14 Te 3 as a potential platform for two-dimensional spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Prototypes of Nonrelativistic Spin Splitting and Polarization in Symmetry Broken Antiferromagnets

Antiferromagnets that break both space-time reversal and translation-spin-rotation symmetries were recently predicted [L.-D. Yuan, Z. Wang, J.-W. Luo, E. I. Rashba, and A. Zunger, Phys. Rev. B 102, 014422 (2020)] to possess splitting between the otherwise spin-degenerate energy bands even without the relativistic spin-orbit coupling (SOC). Here, we point out that such nonrelativistic spin splitting (NRSS)—in particular, “spin splitting type 4” (SST-4) symmetry-broken antiferromagnets—can be divided into subgroups having distinct patterns of spin splitting and spin textures, depending on additional auxiliary symmetries of spin interconversion and polarity. These SST-4 subgroups include the 𝛼-type (no spin-interconverting symmetry) having spin splitting at the Brillouin zone center, as well as the 𝛽 subgroup in which a rotation symmetry is applied and determines the alternating spin texture and the 𝛾 subgroup having exclusively reflection spin-interconverting symmetry. Unlike ferrimagnets, the 𝛼-type compounds are shown to have tiny net magnetization at finite temperature and thus avoid the adverse effect of the stray field. The 𝛼 and 𝛽 subgroups can be either polar or nonpolar, whereas the 𝛾 subgroup is polar only, providing a basis for possible switching by external fields. The combination of NRSS-enabling and auxiliary symmetries is used here as a filter for identifying previously synthesized compounds as specific prototypes. Their characteristic splitting and spin polarization are calculated by density functional theory to the benefit of potential future experimental testing. Interesting results are as follows: (i) SOC-independent NRSS can exceed the magnitude of the SOC-induced Rashba and Dresselhaus spin splitting in semiconductors. (ii) Examples of predicted 𝛼-type insulating compounds include BiCrO 3 (nonpolar) and Mn 2 ⁢ScSbO 6 (polar), the latter having spin splitting of 158 meV and 160 meV in the valence and conduction bands, respectively. (iii) The 𝛽-type (Cu 2 ⁢Y 2 ⁢O 5 and FeF 2 ) and 𝛾-type compounds (Mn 4 ⁢Nb 2 ⁢O 9 and FeScO 3 ) are distinguished both by their auxiliary symmetries and polarity. The spin textures of 𝛾-type compounds are mirror reflected with spin degeneracy of the wave vectors on that mirror. These observations will likely broaden the experimental playing field of NRSS physics significantly.

antiferromagnets↗
DOE OSTI2021

Heterobilayer moiré magnets: Moiré skyrmions and commensurate-incommensurate transitions

In this work, we study untwisted heterobilayers of ferromagnetic and antiferromagnetic van der Waals materials, with in particular a Dzyaloshinskii-Moriya interaction in the ferromagnetic layer. A continuum low-energy field theory is utilized to study such systems. We develop a phase diagram as a function of the strength of interlayer exchange and Dzyaloshinskii-Moriya interactions, combining perturbative and strong coupling analyses with numerical simulations using Landau-Lifshitz-Gilbert equations. Various moiré-periodic commensurate phases are found, and the commensurate-incommensurate transition is discussed. Among the commensurate phases, we observe an interesting skyrmion lattice phase wherein each moiré unit-cell hosts one skyrmion.

2-dimensional systems↗
DOE OSTI2025

Electrodynamics of photo-carriers in multiferroic Eu 0.75 Y 0.25 MnO 3

Understanding and controlling the antiferromagnetic order in multiferroic materials on an ultrafast time scale is a long standing area of interest, due to their potential applications in spintronics and ultrafast magnetoelectric switching. We present an optical pump-terahertz (THz) probe study on multiferroic Eu 0.75 Y 0.25 MnO 3 . The optical pump predominantly excites the d-d transitions of the Mn 3+ ions, and the temporal evolution of the pump-induced transient conductivity is measured with a subsequent THz pulse. Two distinct, temperature-dependent decay times are revealed. The shorter relaxation time corresponds to spin-lattice thermalization, while the longer one is ascribed to electron-hole recombination. A spin-selection rule in the relaxation process is proposed in the magnetic phase. Slight suppression of the electromagnons was observed after the optical pump pulse within the spin-lattice thermalization time scale. These observed fundamental magnetic processes can shed light on ultrafast control of magnetism and photoinduced phase transitions in multiferroics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Intra-molecular coupling within double-segmented molecules impacting magnetic tunnel junction-based molecular spintronics devices

The intra-molecular coupling within multiple units of paramagnetic molecules can produce various effects on molecular spintronics devices (MSD). Here, this paper focuses on double-segmented molecules as the device element to advance understanding of the Impact of internal molecular structure on magnetic tunnel junction-based MSD (MTJMSD). We performed Monte Carlo simulations (MCS) to fill the knowledge gap about the intramolecular coupling role in the magnetic properties of the MTJMSD. This study explored a double-segmented molecule containing two atomic sections, each with a net spin state interacting via Heisenberg exchange coupling within molecules and with ferromagnetic electrodes at different thermal energies, magnetic fields, and coupling strengths. This study also investigated the effect of magnetic field on the double-segmented molecule-based cross-junction-shaped MTJMSD. We also compared the effect of the magnetic field on the mono and double-segmented molecules when connected to two ferromagnetic electrodes. In the strong coupling regime, the intramolecular coupling and molecule coupling with the two ferromagnetic electrodes dominated the MTJMSD response near the molecular junction area. This study provides insight for evaluating the impact of molecular nanostructure internal connectedness on the integrated MSD.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Super-moiré spin textures in twisted two-dimensional antiferromagnets

Stacking two-dimensional layered materials offers a platform to engineer electronic and magnetic states. In general, the resulting states—such as moiré magnetism—have a periodicity at the length scale of the moiré unit cell. Here we study magnetic order in twisted double-bilayer chromium triiodide by means of scanning nitrogen-vacancy microscopy. We observe long-range magnetic textures extending beyond the single moiré unit cell, which we dub a super-moiré magnetic state. At small twist angles, the size of the spontaneous magnetic texture increases with twist angle, opposite to the underlying moiré wavelength. The spin-texture size reaches a maximum of about 300 nm in 1.1° twisted devices, an order of magnitude larger than the underlying moiré wavelength, and vanishes at twist angles above 2°. The obtained magnetic field maps suggest the formation of antiferromagnetic Néel-type skyrmions spanning multiple moiré cells. The twist-angle-dependent study, combined with large-scale atomistic Monte Carlo simulations, suggests that the magnetic competition between the Dzyaloshinskii–Moriya interaction, magnetic anisotropy and exchange interactions—which all depend on the relative rotation of the layers—produces the topological textures that emerge in the super-moiré spin order.

Wong, King Cho [Univ. of Stuttgart (Germany)] (ORC↗
DOE OSTI2020

Thermodynamic signatures of an antiferromagnetic quantum critical point inside a superconducting dome

Recent experiments in unconventional superconductors, and in particular iron-based materials, have reported evidence of an antiferromagnetic quantum critical point (AFM-QCP) emerging inside the superconducting dome of the phase diagram. Fluctuations associated with such an AFM-QCP are expected to promote unusual temperature dependencies of thermodynamic quantities. Here, we compute the T dependence of the specific heat C(T) deep inside a fully gapped s +– superconducting state as the AFM-QCP is approached. We find that at the AFM-QCP, the specific heat C(T) vanishes quadratically with temperature, as opposed to the typical exponential suppression seen in fully gapped BCS superconductors. This robust result is due to a nonanalytic contribution to the free energy arising from the general form of the bosonic (AFM) propagator in the SC state. Away from the AFM-QCP, as temperature is lowered, C(T) shows a crossover from a T2 behavior to an exponential behavior, with the crossover temperature scale set by the value of the superconducting gap and the distance to the QCP. As a result, we argue that these features in the specific heat can be used to unambiguously determine the existence of AFM-QCPs inside the superconducting domes of iron-based and other fully gapped unconventional superconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Spin wave theory for the triaxial magnetic anisotropy 2D van der Waals antiferromagnet CrSBr

The magnetic properties of two-dimensional (2D) materials have been attracting increasing attention in recent years due to their unique behavior and possible applications in new devices. One material of great interest is the 2D van der Waals (vdW) crystal CrSBr, which exhibits antiferromagnetic (AF) order at low temperatures due to an interlayer AF exchange interaction. Here, we present a full quantum spin-wave theory for vdW crystals considering one interlayer and three intralayer exchange interactions, and triaxial magnetic anisotropy. The fits of the theoretical results to antiferromagnetic resonance measurements and inelastic neutron scattering data in CrSBr yield reliable values for the seven interaction parameters that can be used to calculate other properties of this interesting material.

2D materials↗
DOE OSTI2023

Observation of momentum-dependent charge density wave gap in a layered antiferromagnet ${\textrm{Gd}}{\textrm{Te}}_{3}$

Charge density wave (CDW) ordering has been an important topic of study for a long time owing to its connection with other exotic phases such as superconductivity and magnetism. The RTe 3 (R = rare-earth elements) family of materials provides a fertile ground to study the dynamics of CDW in van der Waals layered materials, and the presence of magnetism in these materials allows to explore the interplay among CDW and long range magnetic ordering. Here, we have carried out a high-resolution angle-resolved photoemission spectroscopy (ARPES) study of a CDW material GdTe 3 , which is antiferromagnetic below ~ 12 K, along with thermodynamic, electrical transport, magnetic, and Raman measurements. Our ARPES data show a two-fold symmetric Fermi surface with both gapped and ungapped regions indicative of the partial nesting. The gap is momentum dependent, maximum along $\overline{Γ}$ - $\overline{Z}$ and gradually decreases going towards $\overline{Γ}$ - $\overline{Z}$. Our study provides a platform to study the dynamics of CDW and its interaction with other physical orders in two- and three dimensions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Evidence for spin swapping in an antiferromagnet

Antiferromagnetic insulators offer strategic advantages in spintronic applications because of their negligible stray fields and ultrafast magnetic dynamics. Control of their magnetization and readout of their magnetic state are essential for these applications but remain challenging. In this work, we report the electrical detection of room-temperature magnetization switching in the canted antiferromagnetic insulator LaFeO 3 , capped with a Pt or W overlayer. The observation of a large magneto-thermovoltage with an in-plane temperature gradient suggests that the mechanism is the swapping of spin currents in the antiferromagnet. This effect provides a sensitive electrical probe of the tiny net magnetization in the insulator, which can be manipulated by a magnetic field on the order of 10 mT. Our results highlight a new material class of insulating canted antiferromagnets for spintronics and spin caloritronics and suggests a method for the electrical readout of magnetic signals in an antiferromagnetic insulator. Electrical readout of the state of an antiferromagnet is an important goal for spintronic applications. Now, detection of the electrical voltage created by a thermal gradient in a canted antiferromagnet suggests a route for achieving this goal.

42 ENGINEERING↗
DOE OSTI2022

Charge transport and antiferromagnetic ordering in nitroxide radical crystals

Nonconjugated radical polymers and small molecules are employed as functional materials in organic electronic devices. Furthermore, the unpaired electrons on these materials have permanent magnetic moments, making these materials promising candidates for organic magnets. Through molecular design, strong antiferromagnetic and ferromagnetic ordering have been achieved in conjugated materials. However, the magnetic properties of nonconjugated radical polymers have only shown weak magnetic interactions among the open-shell sites due to the large mean separation between radicals in typical materials. Here, we have designed, synthesized, and crystalized two open-shell molecules that used molecular engineering to control the assembly of the open-shell sites into a strong antiferromagnetically ordered network. The strong antiferromagnetic interaction is evidenced by a high paramagnetic-to-antiferromagnetic transition temperature of ~40 K. This high transition temperature was a result of a high spin exchange coupling constant J of about –20 cm –1 , which was suggested by both experimental and computed coupling parameters given by the energy difference between high-spin and low-spin broken-symmetry structures. In addition, a single-crystal electrical conductivity of ~10 –3 S m –1 was achieved, which indicated the potential of this material in electronic applications. As a result, this work provides an insight into a design strategy for radical-based electronic and magnetic materials through proper molecular structure modifications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

K 2 CoS 2 : A two-dimensional in-plane antiferromagnetic insulator

Recent discovery of two-dimensional (2D) magnetic materials has brought magnetism to the flatland and opened up exciting opportunities for the exploration of fundamental physics as well as novel device applications. Here, we predict a thermodynamically stable 2D magnetic material, ${\mathrm{K}}_{2}{\mathrm{CoS}}_{2}$, which retains its in-plane bulk antiferromagnetic (AFM) order down to the monolayer and bilayer limits. Magnetic moments $(2.5{{\mu}}_{B}/\mathrm{Co})$ are found to form a quasi-one-dimensional antiferromagnetically ordered chain of Co atoms. The nonmagnetic electronic spectrum of the monolayer film is found to host flatbands and van Hove singularities, which play a key role in stabilizing the magnetic ground state. Based on classical Monte Carlo simulations, we estimate the Neel temperature for the AFM monolayer to be ${\approx}15\mathrm{K}$. Our study demonstrates that ${\mathrm{K}}_{2}{\mathrm{CoS}}_{2}$ hosts a robust AFM state which persists from the monolayer limit to the bulk material.

2-dimensional systems↗
DOE OSTI2021

Reversible hydrogen control of antiferromagnetic anisotropy in α-Fe 2 O 3

Antiferromagnetic insulators are a ubiquitous class of magnetic materials, holding the promise of low-dissipation spin-based computing devices that can display ultra-fast switching and are robust against stray fields. However, their imperviousness to magnetic fields also makes them difficult to control in a reversible and scalable manner. Here we demonstrate a novel proof-of-principle ionic approach to control the spin reorientation (Morin) transition reversibly in the common antiferromagnetic insulator α-Fe 2 O 3 (haematite) - now an emerging spintronic material that hosts topological antiferromagnetic spin-textures and long magnon-diffusion lengths. We use a low-temperature catalytic-spillover process involving the post-growth incorporation or removal of hydrogen from α-Fe 2 O 3 thin films. Hydrogenation drives pronounced changes in its magnetic anisotropy, Néel vector orientation and canted magnetism via electron injection and local distortions. We explain these effects with a detailed magnetic anisotropy model and first-principles calculations. Tailoring our work for future applications, we demonstrate reversible control of the room-temperature spin-state by doping/expelling hydrogen in Rh-substituted α-Fe 2 O 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2024

Coercivity enhancement in hematite/permalloy heterostructures across the Morin transition

Interfacial effects between antiferromagnetic (AFM) and ferromagnetic (FM) materials have long been a center of magnetism studies. Aside from the exchange bias occurring at the AFM/FM interface, controlling the coercivity is another significant topic in magnetic recordings. The coercivity of FM materials is often determined through varying grain size, alloy composition, density of defects, etc., which is set during material growth and offers limited room for modification after growth. Hematite (α - Fe 2 O 3 ) is an AFM material that undergoes a temperature-controlled spin-flip transition, the so-called Morin transition. This transition gives an extra degree of freedom making hematite an intriguing component to study the exchange coupling when interfaced with an FM material. Here, in this work, changes in the magnetic properties of soft magnetic permalloy (Ni 81 Fe 19 , or Py) thin films grown on hematite were studied across the Morin transition. Surprisingly, these samples showed a remarkable change in coercivity during the Morin transition. We attribute this effect to the magnetic domain mixture of hematite during the Morin transition. Our findings present a novel method of controlling the coercivity of plain ferromagnetic thin films.

Antiferromagnet↗
DOE OSTI2022

Discovery of charge density wave in a kagome lattice antiferromagnet

A hallmark of strongly correlated quantum materials is the rich phase diagram resulting from competing and intertwined phases with nearly degenerate ground state energies. A well-known example is the copper oxides, where a charge density wave (CDW) is ordered well above and strongly coupled to the magnetic order to form spin-charge separated stripes that compete with superconductivity. Recently, such rich phase diagrams have also been revealed in correlated topological materials. In two-dimensional kagome lattice metals consisting of corner-sharing triangles, the geometry of the lattice can produce flat bands with localized electrons, non-trivial topology, chiral magnetic order, superconductivity and CDW order. While CDW has been found in weakly electron correlated nonmagnetic AV 3 Sb 5 (A = K, Rb, Cs), it has not yet been observed in correlated magnetic ordered kagome lattice metals. Here we report the discovery of CDW within the antiferromagnetic (AFM) ordered phase of kagome lattice FeGe. The CDW in FeGe occurs at wavevectors identical to that of AV 3 Sb 5 , enhances the AFM ordered moment, and induces an emergent anomalous Hall effect. Furthermore, our findings suggest that CDW in FeGe arises from the combination of electron correlations-driven AFM order and van Hove singularities-driven instability possibly associated with a chiral flux phase, in stark contrast to strongly correlated copper oxides and nickelates, where the CDW precedes or accompanies the magnetic order.

36 MATERIALS SCIENCE↗
DOE OSTI2024

2024 roadmap on magnetic microscopy techniques and their applications in materials science

Considering the growing interest in magnetic materials for unconventional computing, data storage, and sensor applications, there is active research not only on material synthesis but also characterisation of their properties. In addition to structural and integral magnetic characterisations, imaging of magnetisation patterns, current distributions and magnetic fields at nano- and microscale is of major importance to understand the material responses and qualify them for specific applications. In this roadmap, we aim to cover a broad portfolio of techniques to perform nano- and microscale magnetic imaging using superconducting quantum interference devices, spin centre and Hall effect magnetometries, scanning probe microscopies, x-ray- and electron-based methods as well as magnetooptics and nanoscale magnetic resonance imaging. The roadmap is aimed as a single access point of information for experts in the field as well as the young generation of students outlining prospects of the development of magnetic imaging technologies for the upcoming decade with a focus on physics, materials science, and chemistry of planar, three-dimensional and geometrically curved objects of different material classes including two-dimensional materials, complex oxides, semi-metals, multiferroics, skyrmions, antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic conductors, superconductors, spintronic and spinorbitronic materials.

2D materials↗