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14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on MnGa by Materials Project

MnGa is Tetraauricupride structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Mn is bonded to four equivalent Mn and eight equivalent Ga atoms to form distorted MnMn4Ga8 cuboctahedra that share corners with twelve equivalent MnMn4Ga8 cuboctahedra, edges with eight equivalent MnMn4Ga8 cuboctahedra, edges with sixteen equivalent GaMn8Ga4 cuboctahedra, faces with eight equivalent GaMn8Ga4 cuboctahedra, and faces with ten equivalent MnMn4Ga8 cuboctahedra. All Mn–Mn bond lengths are 2.72 Å. All Mn–Ga bond lengths are 2.65 Å. Ga is bonded to eight equivalent Mn and four equivalent Ga atoms to form distorted GaMn8Ga4 cuboctahedra that share corners with twelve equivalent GaMn8Ga4 cuboctahedra, edges with eight equivalent GaMn8Ga4 cuboctahedra, edges with sixteen equivalent MnMn4Ga8 cuboctahedra, faces with eight equivalent MnMn4Ga8 cuboctahedra, and faces with ten equivalent GaMn8Ga4 cuboctahedra. All Ga–Ga bond lengths are 2.72 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnGa by Materials Project

MnGa crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are three inequivalent Mn sites. In the first Mn site, Mn is bonded in a 12-coordinate geometry to five Mn and seven Ga atoms. There are a spread of Mn–Mn bond distances ranging from 2.71–2.85 Å. There are a spread of Mn–Ga bond distances ranging from 2.60–2.87 Å. In the second Mn site, Mn is bonded in a 12-coordinate geometry to six Mn and six Ga atoms. There are one shorter (2.59 Å) and two longer (2.81 Å) Mn–Mn bond lengths. There are a spread of Mn–Ga bond distances ranging from 2.59–2.81 Å. In the third Mn site, Mn is bonded to six equivalent Mn and six equivalent Ga atoms to form MnMn6Ga6 cuboctahedra that share faces with two equivalent GaMn12 cuboctahedra. All Mn–Ga bond lengths are 2.64 Å. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded in a 11-coordinate geometry to six Mn and five Ga atoms. There are a spread of Ga–Ga bond distances ranging from 2.67–2.98 Å. In the second Ga site, Ga is bonded in a 6-coordinate geometry to six Mn and two equivalent Ga atoms. In the third Ga site, Ga is bonded to twelve Mn atoms to form GaMn12 cuboctahedra that share faces with two equivalent MnMn6Ga6 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(MnGa)6 by Materials Project

Ho(MnGa)6 crystallizes in the orthorhombic Fmmm space group. The structure is three-dimensional. Ho is bonded in a 12-coordinate geometry to eight Mn and twelve Ga atoms. There are four shorter (3.17 Å) and four longer (3.36 Å) Ho–Mn bond lengths. There are eight shorter (3.23 Å) and four longer (3.41 Å) Ho–Ga bond lengths. There are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a 12-coordinate geometry to two equivalent Ho, six Mn, and four equivalent Ga atoms. There are two shorter (2.41 Å) and four longer (2.69 Å) Mn–Mn bond lengths. All Mn–Ga bond lengths are 2.47 Å. In the second Mn site, Mn is bonded in a 10-coordinate geometry to one Ho, seven Mn, and six Ga atoms. There are a spread of Mn–Mn bond distances ranging from 2.61–3.08 Å. There are a spread of Mn–Ga bond distances ranging from 2.57–2.76 Å. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded to two equivalent Ho, four equivalent Mn, and six Ga atoms to form a mixture of distorted face and corner-sharing GaHo2Mn4Ga6 cuboctahedra. There are two shorter (2.41 Å) and four longer (2.62 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 12-coordinate geometry to two equivalent Ho, six Mn, and two equivalent Ga atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu(MnGa)6 by Materials Project

Lu(MnGa)6 crystallizes in the orthorhombic Fmmm space group. The structure is three-dimensional. Lu is bonded in a 12-coordinate geometry to eight Mn and twelve Ga atoms. There are four shorter (3.14 Å) and four longer (3.32 Å) Lu–Mn bond lengths. There are eight shorter (3.21 Å) and four longer (3.42 Å) Lu–Ga bond lengths. There are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a 12-coordinate geometry to two equivalent Lu, four equivalent Mn, and four equivalent Ga atoms. All Mn–Mn bond lengths are 2.69 Å. All Mn–Ga bond lengths are 2.46 Å. In the second Mn site, Mn is bonded in a 10-coordinate geometry to one Lu, seven Mn, and six Ga atoms. There are a spread of Mn–Mn bond distances ranging from 2.62–3.10 Å. There are a spread of Mn–Ga bond distances ranging from 2.57–2.79 Å. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded to two equivalent Lu, four equivalent Mn, and six Ga atoms to form a mixture of distorted face and corner-sharing GaLu2Mn4Ga6 cuboctahedra. There are two shorter (2.42 Å) and four longer (2.61 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 12-coordinate geometry to two equivalent Lu, six Mn, and four Ga atoms. There are one shorter (2.91 Å) and one longer (3.06 Å) Ga–Ga bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnGa(CuSe2)2 by Materials Project

MnGa(CuSe2)2 is Stannite-like structured and crystallizes in the tetragonal I-4 space group. The structure is three-dimensional. Mn2+ is bonded to four equivalent Se2- atoms to form MnSe4 tetrahedra that share corners with four equivalent GaSe4 tetrahedra and corners with eight CuSe4 tetrahedra. All Mn–Se bond lengths are 2.47 Å. There are two inequivalent Cu+1.50+ sites. In the first Cu+1.50+ site, Cu+1.50+ is bonded to four equivalent Se2- atoms to form CuSe4 tetrahedra that share corners with four equivalent MnSe4 tetrahedra, corners with four equivalent CuSe4 tetrahedra, and corners with four equivalent GaSe4 tetrahedra. All Cu–Se bond lengths are 2.42 Å. In the second Cu+1.50+ site, Cu+1.50+ is bonded to four equivalent Se2- atoms to form CuSe4 tetrahedra that share corners with four equivalent MnSe4 tetrahedra, corners with four equivalent CuSe4 tetrahedra, and corners with four equivalent GaSe4 tetrahedra. All Cu–Se bond lengths are 2.42 Å. Ga3+ is bonded to four equivalent Se2- atoms to form GaSe4 tetrahedra that share corners with four equivalent MnSe4 tetrahedra and corners with eight CuSe4 tetrahedra. All Ga–Se bond lengths are 2.46 Å. Se2- is bonded to one Mn2+, two Cu+1.50+, and one Ga3+ atom to form corner-sharing SeMnGaCu2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnGa by Materials Project

MnGa crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Mn is bonded to six equivalent Mn and six equivalent Ga atoms to form distorted MnMn6Ga6 cuboctahedra that share corners with eighteen equivalent MnMn6Ga6 cuboctahedra, edges with six equivalent MnMn6Ga6 cuboctahedra, edges with twelve equivalent GaMn6Ga6 cuboctahedra, faces with eight equivalent MnMn6Ga6 cuboctahedra, and faces with twelve equivalent GaMn6Ga6 cuboctahedra. All Mn–Mn bond lengths are 2.75 Å. All Mn–Ga bond lengths are 2.60 Å. Ga is bonded to six equivalent Mn and six equivalent Ga atoms to form distorted GaMn6Ga6 cuboctahedra that share corners with eighteen equivalent GaMn6Ga6 cuboctahedra, edges with six equivalent GaMn6Ga6 cuboctahedra, edges with twelve equivalent MnMn6Ga6 cuboctahedra, faces with eight equivalent GaMn6Ga6 cuboctahedra, and faces with twelve equivalent MnMn6Ga6 cuboctahedra. All Ga–Ga bond lengths are 2.75 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Anisotropic resistance with a 90° twist in a ferromagnetic Weyl semimetal, Co 2 MnGa

Weyl semimetals exhibit exotic magnetotransport phenomena such as the chiral anomaly and surface-to-bulk quantum oscillations (Weyl orbits) due to chiral bulk states and topologically protected surface states. Here we report a unique transport property in crystals of the ferromagnetic nodal-line Weyl semimetal Co 2 MnGa that have been polished to micron thicknesses using a focused ion beam. These thin crystals exhibit a large planar resistance anisotropy (10 × ) with axes that rotate by 90 degrees between opposite faces of the crystal. We use symmetry arguments and electrostatic simulations to show that the observed anisotropy resembles that of an isotropic conductor with surface states that are impeded from hybridization with bulk states. The origin of these states awaits further experiments that can correlate the surface bands with the observed 90° twist.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Unraveling magneto-structural coupling of Ni 2 MnGa alloy under the application of stress and magnetic field using in situ polarized neutron diffraction

The magneto-structural evolution of a Ni 2 MnGa single crystal was investigated by in situ polarized neutron diffraction under both magnetic field and mechanical loading. The ability to separate the nuclear and magnetic scatterings by polarized neutrons enables simultaneous observations of the twin reorientation (through twin boundary motion) and magnetic moment configuration. It is found that under a 1.0 T saturating magnetic field, twin reorientation can be activated by compressive stress and is accompanied by a realignment of the magnetic moment, which follows the easy axis of the twin variant. On the other hand, compressive stress as small as 1.0 MPa can freeze the twin reorientation. The evolution of the magnetic scattering amplitudes suggests that the change in magnetization was mainly achieved through the magnetic domain wall motion, while the twin boundary motion was blocked.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Magnetic and transport properties of amorphous, B 2 and L 2 1 Co 2 MnGa thin films

We have studied the magnetic and transport properties of Co 2 MnGa (CMG) thin films grown on MgO(100) substrates in terms of their chemical evolution from amorphous to ordered L 2 1 phases at the substrate temperature T s during the thin film deposition. Interestingly, the chemical order and magnetic properties sharply change depending on T s . The CMG film deposited at T s = 550 °C exhibits the L 2 1 -ordered structure and the magnetization of 3.5 μ B /f.u., while the CMG film deposited at T s = 300 °C shows a B 2-ordered structure and a relatively lower magnetization of 3 μ B /f.u., possibly due to the Mn–Mn antiferromagnetic interactions. A metallic behavior of the electrical resistivity appeared in the CMG film deposited at T s = 550 °C, whereas the semiconducting behavior appeared in the CMG films deposited at 300 °C and room temperature. Moreover, we found that the absolute value of α = d(Δ ρ )/d( T 1/2 ) in the low-temperature range below about 20 K is a measure to evaluate the degree of the chemical disorder. In a Hall effect measurement, the L 2 1 -ordered CMG film obtained at T s = 550 °C shows a sizable anomalous Hall resistivity of 15 µ Ω cm. This study unveils the relation between T s and atomic ordering, providing a new pathway for optimizing the chemical order.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Unraveling the structural dependency of Weyl nodes in Co 2 MnGa

Conventionally, the modulation of the intrinsic Weyl nodes in Weyl semimetals is challenging, due to topological protection. Here we report the structural dependence of the Weyl nodes in a Co2⁢MnGa Heusler thin film via a temperature-dependent tetragonal distortion. The ability to manipulate these Weyl nodes allows for the control of the intrinsic electromagnetic properties. Temperature-dependent x-ray diffraction (XRD) measurements identify a compressive tetragonal distortion with decreasing temperature from 300 to 20 K. The calculated Weyl properties can be directly compared with experimental parameters through the temperature-dependent XRD measurements which show the intrinsic correlation between Weyl properties and important magnetic parameters. Further, the microscopic momentum space properties of Weyl nodes such as the distance (d W ), solid angle (Ω W ), tilt (φ W ), and nodal point energy (E W ) directly affect the macroscopic observable properties such as exchange stiffness (A), magnetization (M), and effective anisotropy field $H^{eff}_{K}$, as shown via structure-dependent density functional theory calculations. These predictions are experimentally observed as large variations in the bulk magnetization and effective anisotropy field as a function of temperature. These results highlight a unique degree of freedom in the control of macroscopic magnetic properties via the modulation of the intrinsic properties of Weyl nodes through structural distortions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Experimental and theoretical investigation of the crystalline surface, film, and interface properties of antiperovskite Mn 3 GaN grown by molecular beam epitaxy on MgO(001)

Here, we present a study of the epitaxial growth, characterization, and theoretical modeling of thin film antiperovskite Mn 3 GaN, an antiferromagnetic material with kagome structure which is grown on MgO (001) substrates using N-plasma-assisted molecular beam epitaxy. Reflection high energy electron diffraction is used to assess the in-plane evolution of the film structure during growth, and the surface is investigated in-situ using scanning tunneling microscopy and Auger electron spectroscopy. These results are combined with precision measurements done ex-situ determining the film lattice constants using a combination of x-ray diffraction with reciprocal space mapping and scanning transmission electron microscopy. Overall, a uniform, homogeneous film with an atomically smooth vacuum surface and atomically sharp substrate interface is found having very small in-plane tensile strain and mild out-of-plane compressive strain. First-principles theoretical calculations are applied in order to ascertain the lowest energy models for both the Mn 3 GaN surface and the Mn 3 GaN/MgO film/substrate interface. Models including MnGa versus MnN surface layers and MnGa versus MnN interfacial layers are considered as functions of both the Mn and Ga chemical potentials. The predictions are discussed in comparison to the experimental results. The overall findings suggest that Mn 3 GaN on MgO(001) is a viable epitaxial film which can be further explored in connection with antiferromagnetic spintronics.

Density functional theory↗
DOE OSTI2023

Control of ternary alloy composition during remote epitaxy on graphene

Understanding the sticking coefficient σ, i.e., the probability of an adatom sticking to a surface, is essential for controlling the stoichiometry during epitaxial film growth. However, σ on monolayer graphene-covered surfaces and its impact on remote epitaxy are not understood. Here, using molecular-beam epitaxial growth of the magnetic shape memory alloy Ni 2 MnGa, we show that the sticking coefficients for metals on graphene-covered MgO (001) are less than one and are temperature and element dependent, as revealed by ion backscattering spectrometry and energy-dispersive x-ray spectroscopy. This lies in stark contrast with most transition metals sticking on semiconductor and oxide substrates, for which σ is near unity at typical growth temperatures (T < 800°C). By initiating growth below 400°C, where the sticking coefficients are closer to unity and wetting on the graphene surface is improved, we demonstrate the epitaxy of Ni 2 MnGa films with controlled stoichiometry that can be exfoliated to produce freestanding membranes. Straining these membranes tunes the magnetic coercive field. Finally, our results provide a route to synthesize membranes with complex stoichiometries whose properties can be manipulated via strain.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub–100-fs time scales

The direct manipulation of spins via light may provide a path toward ultrafast energy-efficient devices. However, distinguishing the microscopic processes that can occur during ultrafast laser excitation in magnetic alloys is challenging. Here, we study the Heusler compound Co 2 MnGa, a material that exhibits very strong light-induced spin transfers across the entire M-edge. By combining the element specificity of extreme ultraviolet high-harmonic probes with time-dependent density functional theory, we disentangle the competition between three ultrafast light-induced processes that occur in Co 2 MnGa: same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast spin flips mediated by spin-orbit coupling. By measuring the dynamic magnetic asymmetry across the entire M-edges of the two magnetic sublattices involved, we uncover the relative dominance of these processes at different probe energy regions and times during the laser pulse. Our combined approach enables a comprehensive microscopic interpretation of laser-induced magnetization dynamics on time scales shorter than 100 femtoseconds.

36 MATERIALS SCIENCE↗