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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Quantum Sensing and Imaging of Spin–Orbit-Torque-Driven Spin Dynamics in the Non-Collinear Antiferromagnet Mn 3 Sn

Novel non-collinear antiferromagnets with spontaneous time-reversal symmetry breaking, non-trivial band topology, and unconventional transport properties have received immense research interest over the past decade due to their rich physics and enormous promise in technological applications. One of the central focuses in this emerging field is exploring the relationship between the microscopic magnetic structure and exotic material properties. Nanoscale imaging of both spin–orbit-torque-induced deterministic magnetic switching and chiral spin rotation in non-collinear antiferromagnet Mn 3 Sn films using nitrogen-vacancy (NV) centers are reported. Direct evidence of the off-resonance dipole–dipole coupling between the spin dynamics in Mn 3 Sn and proximate NV centers is also demonstrated by NV relaxometry measurements. These results demonstrate the unique capabilities of NV centers in accessing the local information of the magnetic order and dynamics in these emergent quantum materials and suggest new opportunities for investigating the interplay between topology and magnetism in a broad range of topological magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electrically Controlled All-Antiferromagnetic Tunnel Junctions on Silicon with Large Room-Temperature Magnetoresistance

Antiferromagnetic (AFM) materials are a pathway to spintronic memory and computing devices with unprecedented speed, energy efficiency, and bit density. Realizing this potential requires AFM devices with simultaneous electrical writing and reading of information, which are also compatible with established silicon-based manufacturing. Recent experiments have shown tunneling magnetoresistance (TMR) readout in epitaxial AFM tunnel junctions. However, these TMR structures are not grown using a silicon-compatible deposition process, and controlling their AFM order required external magnetic fields. Here are shown three-terminal AFM tunnel junctions based on the noncollinear antiferromagnet PtMn 3 , sputter-deposited on silicon. The devices simultaneously exhibit electrical switching using electric currents, and electrical readout by a large room-temperature TMR effect. First-principles calculations explain the TMR in terms of the momentum-resolved spin-dependent tunneling conduction in tunnel junctions with noncollinear AFM electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2024

UOTe: Kondo‐Interacting Topological Antiferromagnet in a Van der Waals Lattice

Since the initial discovery of 2D van der Waals (vdW) materials, significant effort has been made to incorporate the three properties of magnetism, band structure topology, and strong electron correlations—to leverage emergent quantum phenomena and expand their potential applications. However, the discovery of a single vdW material that intrinsically hosts all three ingredients has remained an outstanding challenge. Here, in this work, the discovery of a Kondo-interacting topological antiferromagnet is reported in the vdW 5f electron system UOTe. It has a high antiferromagnetic (AFM) transition temperature of 150 K, with a unique AFM configuration that breaks the combined parity and time reversal (PT) symmetry in an even number of layers while maintaining zero net magnetic moment. This angle-resolved photoemission spectroscopy (ARPES) measurements reveal Dirac bands near the Fermi level, which combined with the theoretical calculations demonstrate UOTe as an AFM Dirac semimetal. Within the AFM order, the presence of the Kondo interaction is observed, as evidenced by the emergence of a 5ƒ flat band near the Fermi level below 100 K and hybridization between the Kondo band and the Dirac band. The density functional theory calculations in its bilayer form predict UOTe as a rare example of a fully-compensated AFM Chern insulator.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Low-Frequency Electronic Noise in Quasi-2D van der Waals Antiferromagnetic Semiconductor FePS 3 —Signatures of Phase Transitions

Here, low-frequency current fluctuations, i.e., noise, in the quasi-2D van der Waals antiferromagnetic semiconductor FePS 3 with the electronic bandgap of 1.5 eV is investigated. The electrical and noise characteristics of the p-type, highly resistive, thin films of FePS 3 are measured at different temperatures. The noise spectral density is of the 1/f-type over most of the examined temperature range but reveals well-defined Lorentzian bulges, and increases strongly near the Néel temperature T N =118 K (f is the frequency). Intriguingly, the noise spectral density attains its minimum at temperature T≈200 K, which is attributed to an interplay of two opposite trends in noise scaling—one for semiconductors and another for materials with the phase transitions. The Lorentzian corner frequencies reveal unusual dependence on temperature and bias voltage, suggesting that their origin is different from the generation—recombination noise in conventional semiconductors. The obtained results are important for proposed applications of antiferromagnetic semiconductors in spintronic devices. They also attest to the power of the noise spectroscopy for monitoring various phase transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic Susceptibility and Neutron Scattering of Graphene in Antiferromagnetic State: a Tight-Binding Approach

We address here a tight-binding model study of the frequency-dependent antiferromagnetic spin susceptibility for the graphene systems. The Hamiltonian consists of electron hopping up to the third-nearest-neighbors, substrate and impurity effects in presence of electron-electron interactions at A and B sub-lattices. To calculate susceptibility, we evaluate the two-particle electron Green’s function by using Zubarev’s Green’s function technique. The frequency-dependent antiferromagnetic susceptibility of the system is computed numerically by taking 1000 X 1000 grid points of the electron momentum. The susceptibility displays a sharp peak at the neutron momentum transfer energy at low energies and another higher-energy peak associated with the substrate-induced gap. The evolution of these two peaks are investigated by varying neutron wave vector, Coulomb correlation energy, substrate-induced gap, electron hopping integrals and A- and B-site electron-doping concentrations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Antiferromagnetic Ordering at Room Temperature in Co-Doped Sb{sub 2}Te{sub 3} Topological Insulators

Structural and magnetic properties of Co-doped Sb{sub 2}Te{sub 3} topological insulators have been investigated. Surface morphology was studied using scanning electron microscope (SEM) and atomic force microscope (AFM). X-ray photo electron spectroscopy (XPS) study reveals the mixed states of Co in Co{sup 2+} and Co{sup 3+}. Magnetic study indicates that the substitution of Co in Sb{sub 2}Te{sub 3} not only tune the materials from diamagnetic to antiferromagnetic (even at room temperature) but also propose a promising materials for antiferromagnetic TI which may be useful even for room temperature applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Phase Diagrams of a 2D Dilute Antiferromagnetic Ising Model with Charged Impurities

In this work, we address a topical problem of a competition of charge and spin ordering for high-T cuprates. We have studied a simplified static 2D spin-pseudospin model on a square lattice, which takes into account both conventional antiferromagnetic spin exchange coupling and the on-site and intersite charge correlations in the CuO{sub 2} planes with the on-site Hilbert space reduced to only three effective valent states. We compared an analytical results for the ground state and for the temperature phase diagrams obtained in a mean field approximation and a large amount of the classical Monte Carlo calculations. Numerical results show that homogeneous ground state antiferromagnetic solutions found in a mean field approximation are unstable for the “strong” exchange limit with respect to phase separation with the charge and spin subsystems behaving like immiscible quantum liquids. We found an analytical expression for critical temperature of phase separation and performed the comparison with the Monte Carlo results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Proximity Effects of Superconductivity and Antiferromagnetism in a Nanowire

In this paper, we theoretically study the proximity effects of s-wave superconductivity(SC) and antiferromagnetism(AFM) in a nanowire. For the half-filling case, it was found that the Andreev bound states form near the boundary between the AFM and the SC which are accompanied by the strongly localized p-wave pairing. These in-gap states remain when the system is slightly doped. For the electron or hole doped system, they merge into the upper or the lower antiferromagnetic bands gradually with the increase of doping, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Structural and magnetic properties of ferrimagnetic ε-phase Mn 4 N and antiferromagnetic ζ-phase Mn10N thin films on MgO(001)

Single phase ε-Mn 4 N and ζ-Mn 10 N thin films are grown on MgO(001) using molecular beam epitaxy. The films are identified and characterized using reflection high-energy electron diffraction, x-ray diffraction, back scattered electron scanning electron microscopy, atomic/magnetic force microscopy and Rutherford backscattering spectrometry. These films are found to be highly smooth with root-mean-squared roughnesses 3.39 nm and below. The quality of ε-Mn 4 N grown is strongly dependent on substrate temperature during growth. Epitaxial growth of substantial grains composed of the antiferromagnetic η-phase Mn 3 N 2 side by side with ferrimagnetic ε-phase grains is observed when growth temperature is below 480 °C. Ising domains isolated within areas roughly 0.5 μm across are observed in the ferrimagnetic ε-phase grains of samples consisting of a mix of η- and ε-phase grains. Magnetic domains following semi-continuous paths, which are 0.7–7.2 μm across, are observed in single phase ε-Mn4N. Measurements of the ζ-phase detail the structure and magnetism of the material as high Mn content γ-type ζ-phase with a regular surface corrugation along the [100]-direction and antiferromagnetic.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Applying a difference ratio method in spin-polarized scanning tunneling microscopy to determine crystalline anisotropies and antiferromagnetic spin alignment in Cr(0 0 1) c(2 $\times$ 2)

Here, we present spin-polarized scanning tunneling microscopy results for 8 micrometer thick, chromium (0 0 1)-oriented thin films deposited using molecular beam epitaxy on MgO(0 0 1) substrates, achieving a smooth, atomically-stepped staircase morphology. The c(2 × 2) surface structure of the Cr(0 0 1) surface was found via atomically-resolved scanning tunneling microscopy images and dI/dV spectroscopy. A practical method of interpreting spin-polarized scanning tunneling microscopy dI/dV images was developed and applied to the c(2 × 2) Cr(0 0 1) surface structure. A 180° spin reversal between atomic layers, characteristic of a topological, layer-wise antiferromagnetic spin structure, was quantitatively verified. In addition, the spin anisotropy directions for 3 different antiferromagnetic, atomic staircase domains occurring on the c(2 × 2) surface were quantitatively determined to coincide with the [1 0 0], [0 1 0], and [1 1 0] crystallographic axes of chromium

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis, structure and magnetic properties of La{sub 3}Co{sub 2}SbO{sub 9}: A double perovskite with competing antiferromagnetic and ferromagnetic interactions

The synthesis, structural characterization, and magnetic properties of La{sub 3}Co{sub 2}SbO{sub 9} double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P2{sub 1}/n. Co{sup 2+} and Sb{sup 5+} have the maximum order allowed for the La{sub 3}Co{sub 2}SbO{sub 9} stoichiometry. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a=5.6274(2) A, b=5.6842(2) A, c=7.9748(2) A and {beta}=89.999(3) Degree-Sign . Magnetization measurements indicate the presence of ferromagnetic correlations with T{sub C}=55 K attributed to the exchange interactions for non-linear Co{sup 2+}-O-Sb{sup 5+}-O-Co{sup 2+} paths. The effective magnetic moment obtained experimentally is {mu}{sub exp}=4.38 {mu}{sub B} (per mol Co{sup 2+}), between the theoretical one for spin only (3.87 {mu}{sub B}) and spin-orbit value (6.63 {mu}{sub B}), indicating partially unquenched contribution. The low magnetization value at high magnetic field and low temperature (1 {mu}{sub B}/f.u., 5 T and 5 K) and the difference between ZFC and FC magnetization curves (at 5 kOe) indicate that the ferromagnetism do not reach a long range order and that the material has an important magnetic frustration. - Graphical abstract: Co-O-Co (Yellow octahedra only) rich zones (antiferromagnetic) are in contact with Co-O-Sb-O-Co (Red and yellow octahedra) rich zones (Ferromagnetic) to give the peculiar magnetic properties, as a consequence, a complex hysteresis loop can be observed composed by a main and irreversible curve in all the measured range, superimposed with a ferromagnetic component at low fields. Highlights: Black-Right-Pointing-Pointer La{sub 3}Co{sub 2}SbO{sub 9} has small Goldschmidt Tolerance Factor (t) due to the small size of La{sup 3+}. Black-Right-Pointing-Pointer Small t determines an angle for the path Co{sup 2+}-O-Sb{sup 5+}-O-Co{sup 2+} of 153 Degree-Sign . Black-Right-Pointing-Pointer Ferromagnetism is attributed to exchange interactions for Co{sup 2+}-O-Sb{sup 5+}-O-Co{sup 2+} paths. Black-Right-Pointing-Pointer Ferromagnetic nanoclusters are embedded in an antiferromagnetic matrix.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Antiferromagnetic transitions of osmium-containing rare earth double perovskites Ba{sub 2}LnOsO{sub 6} (Ln=rare earths)

The perovskite-type compounds containing both rare earth and osmium Ba{sub 2}LnOsO{sub 6} (Ln=Pr, Nd, Sm–Lu) have been prepared. Powder X-ray diffraction measurements and Rietveld analysis show that Ln{sup 3+} and Os{sup 5+} ions are structurally ordered at the M site of the perovskite BaMO{sub 3}. Magnetic susceptibility and specific heat measurements show that an antiferromagnetic ordering of Os{sup 5+} ions has been observed for Ba{sub 2}LnOsO{sub 6} (Ln=Pr, Nd, Sm, Eu, Gd, Lu) at 65–71 K. Magnetic ordering of Ln{sup 3+} moments occurs when the temperature is furthermore decreased. - Graphical abstract: The perovskite-type compounds containing both rare earth and osmium Ba{sub 2}LnOsO{sub 6} (Ln=Pr, Nd, Sm–Lu) have been prepared. An antiferromagnetic ordering of Os{sup 5+} ions has been observed for Ba{sub 2}LnOsO{sub 6} (Ln=Pr, Nd, Sm, Eu, Gd, Lu) at 65–71 K. Measurements and analysis of the specific heat for Ba{sub 2}PrOsO{sub 6} show that magnetic ordering of the Pr{sup 3+} moments should have occurred at ∼20 K. Display Omitted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Structural phase transition and antiferromagnetic transition of Tb{sub 3}RuO{sub 7}

Magnetic properties and structural phase transition of terbium ruthenate Tb{sub 3}RuO{sub 7} are investigated through magnetic susceptibility, specific heat, high-temperature X-ray diffraction and differential scanning calorimetry measurements. The structural phase transition from space group P2{sub 1}nb to Cmcm has been observed at 402 K. Tb{sub 3}RuO{sub 7} shows an antiferromagnetic transition at 17 K. In addition, another magnetic anomaly has been found at 10 K. Analysis of the magnetic specific heat for Tb{sub 3}RuO{sub 7} indicates that the magnetic transitions at 10 and 17 K are due to the magnetic ordering of Tb{sup 3+} and Ru{sup 5+} ions, respectively. - Graphical abstract: Temperature dependence of the magnetic specific heat divided by temperature (C{sub mag}/T) and the magnetic entropy (S{sub mag}) for Tb{sub 3}RuO{sub 7}. Two-step magnetic transition has been observed. - Highlights: • Tb{sub 3}RuO{sub 7} shows an antiferromagnetic transition at 17 K. • Specific heat measurements confirmed the occurrence of two-step magnetic transition. • The phase transition from space group P2{sub 1}nb to Cmcm has been observed at 402 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Synthesis and characterization of the novel antiferromagnet LaNiB 3 O 7

Here, we present the synthesis, structure, and magnetic properties of the novel borate LaNiB 3 O 7 - the first magnetically ordered compound reported in the CaAlB 3 O 7 structure type. This material is made of alternating sheets of corner-sharing borate tetrahedra and planes of La and Ni ions, with distorted nickel oxide [NiO 6 ] octahedra and lanthanum oxide [LaO 10 ] polyhedra. Temperature-dependent magnetic susceptibility data reveal dominantly antiferromagnetic interactions and an antiferromagnetic transition with a Neel temperature of 19 K, confirmed by specific heat data. The magnetic moment per nickel ion is 3.06 μ B . This compound uncovers a new family of rare-earth transition-metal borates to probe for magnetic interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Real-space visualization of short-range antiferromagnetic correlations in a magnetically enhanced thermoelectric

Short-range magnetic correlations can significantly increase the thermopower of magnetic semiconductors, representing a noteworthy development in the decades-long effort to develop high-performance thermoelectric materials. Here, we reveal the nature of the thermopower-enhancing magnetic correlations in the antiferromagnetic semiconductor MnTe. Using magnetic pair distribution function analysis of neutron scattering data, we obtain a detailed, real-space view of robust, nanometer-scale, antiferromagnetic correlations that persist into the paramagnetic phase above the Neel temperature $T_N$ = 307 K. In this work, the magnetic correlation length in the paramagnetic state is significantly longer along the crystallographic c axis than within the ab plane, pointing to anisotropic magnetic interactions. Ab initio calculations of the spin-spin correlations using density functional theory in the disordered local moment approach reproduce this result with quantitative accuracy. These findings constitute the first real-space picture of short-range spin correlations in a magnetically enhanced thermoelectric and inform future efforts to optimize thermoelectric performance by magnetic means.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Extraordinary Magnetic Response of an Anisotropic 2D Antiferromagnet via Site Dilution

A prominent characteristic of 2D magnetic systems is the enhanced spin fluctuations, which reduce the ordering temperature. We report that a magnetic field of only 1000th of the Heisenberg superexchange interaction can induce a crossover, which for practical purposes is the effective ordering transition, at temperatures about 6 times the Néel transition in a site-diluted two-dimensional anisotropic quantum antiferromagnet. Such a strong magnetic response is enabled because the system directly enters the antiferromagnetically ordered state from the isotropic disordered state, skipping the intermediate anisotropic stage. The underlying mechanism is achieved on a pseudospin-half square lattice realized in the [(SrIrO3)1/(SrTiO3)2] superlattice thin film that is designed to linearly couple the staggered magnetization to external magnetic fields by virtue of the rotational symmetry-preserving Dzyaloshinskii–Moriya interaction. Furthermore, our model analysis shows that the skipping of the anisotropic regime despite finite anisotropy is due to the enhanced isotropic fluctuations under moderate dilution.

2D antiferromagnet↗
DOE OSTI2019

Atomically Thin CrCl 3 : An In-Plane Layered Antiferromagnetic Insulator

The recent discovery of magnetism in atomically thin layers of van der Waals (vdW) crystals has created new opportunities for exploring magnetic phenomena in the two-dimensional (2D) limit. In most 2D magnets studied to date, the c-axis is an easy axis, so that at zero applied field the polarization of each layer is perpendicular to the plane. In this work, we demonstrate that atomically thin CrCl 3 is a layered antiferromagnetic insulator with an easy-plane normal to the c-axis, that is, the polarization is in the plane of each layer and has no preferred direction within it. Ligand-field photoluminescence at 870 nm is observed down to the monolayer limit, demonstrating its insulating properties. We investigate the in-plane magnetic order using tunneling magnetoresistance in graphene/CrCl 3 /graphene tunnel junctions, establishing that the interlayer coupling is antiferromagnetic down to the bilayer. From the temperature dependence of the magnetoresistance, we obtain an effective magnetic phase diagram for the bilayer. Our findings suggest that CrCl 3 should be useful for studying the physics of 2D phase transitions and for making new kinds of vdW spintronic devices.

2D magnetic insulator↗
DOE OSTI2021

Spin Reorientation in Antiferromagnetic Layered FePt 5 P

FePt 5 P, a substitutional variant of the anti-CeCoIn 5 structure type in the space group P4/mmm, was synthesized by a high-temperature solid-state method and structurally characterized by X-ray diffraction. FePt 5 P contains layers of FePt 12 clusters formed by magnetically active Fe and heavy Pt with strong spin-orbit coupling (SOC); the layers are separated by P atoms. The various Fe–Pt distances in FePt 12 clusters generate complex magnetic orders in FePt 5 P. According to temperature-dependent magnetic and specific heat measurements, FePt 5 P shows a stripe-type antiferromagnetic order at T N ≈ 90 K, which is also confirmed by resistivity measurements. Furthermore, a spin reorientation occurs at ~74 and ~68 K in and out of the ab plane based on the specific heat measurements. The temperature-dependent neutron powder diffraction patterns demonstrate the antiferromagnetic order in FePt 5 P, and the spins orientate up to 58.4° with respect to the c axis at 10 K. First-principles calculations of FePt 5 P show the band splitting at the Fermi level by strong SOC and the s–d hybridization between P and Fe/Pt electrons enhances the structural stability and affects the magnetic ordering.

36 MATERIALS SCIENCE↗