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At least 19 records

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DOE OSTI2025

Driving rapid atomic order in MnAl via low-magnitude magnetic field annealing

Application of a mild (60 mT), uniform magnetic field during short-term thermal treatment of kinetically retained, atomically disordered (paramagnetic) ε-MnAl was found to deliver a significant ~50 % increase in the formation of L1 0 atomically ordered (ferromagnetic) τ-MnAl product phase, compared to that produced by conventional (i.e., zero-field) annealing under identical thermal conditions. The magnetic field, applied in a passive closed-circuit configuration during annealing, induced significant changes in the structural, magnetic, and phase evolution of the material. Computational results based on electronic structure calculations demonstrate that the effective magnetic susceptibility of τ-MnAl is sensitive to the orientation, rather than the magnitude, of an applied magnetic field in the vicinity of the Curie temperature. The uniaxial magnetocrystalline anisotropy of the L1 0 structure is proposed to act as a filter for selective propagation of the population of τ-MnAl variants that are favorably aligned with the applied field. In this manner, crystallographic “gridlock” is alleviated that would otherwise arise from the coexistence of multiple, energetically equivalent τ-phase variants within the parent ε-phase matrix. These results confirm that static, low-magnitude magnetic field annealing is able to accelerate L1 0 atomic ordering in the MnAl system and likely can exert similar influences in relevant magnetic systems, facilitating efficient tailoring of structure-sensitive magnetic properties for the manufacture of magnetic materials.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Anomalous Nernst and Seebeck coefficients in epitaxial thin film Co 2 MnAl x Si 1 - x and Co 2 FeAl

Here we have measured the Seebeck and anomalous Nernst coefficients and corresponding transverse and longitudinal thermoelectric conductivities from 2 to 400 K in thin film (thickness t ~10 nm) Co 2 MnAl x Si 1-x (0 ≤ x ≤ 1) and Co 2 FeAl grown by molecular beam epitaxy (MBE). A large (-14 A m -1 K -1 at 300 K) anomalous component of the transverse thermoelectric conductivity is observed in Co 2 MnAl, especially as contrasted to Co 2 MnSi (0.28 A m -1 K -1 at 300 K). This enhancement is likely due to Weyl points close to the Fermi level of Co 2 MnAl which disappear as x decreases.

36 MATERIALS SCIENCE↗

DOE OSTI2023

L1 0 Ordering in MnAl and FeNi Influenced by Magnetic Field and Strain

Due to various materials supply chain challenges, magnets free of constrained elements are attracting increasing interest. Magnetic materials such as rare-earth free FeNi and MnAl have been receiving considerable attention due to the high magnetocrystalline anisotropy and other associated magnetic properties derived from their unique chemically ordered tetragonal crystal structure, denoted as the L1 0 structure. However, synthesis of L1 0 FeNi has had limited success due to the extremely low atomic mobilities of Fe and Ni. In this work, isostructural MnAl was first studied as proxy to understand the L1 0 ordering process. Here, evidence of L1 0 ordering in FeNi derived from TEM studies is presented, where ordering was facilitated by the application of strain and magnetic field provided during thermal treatment of a severely plastically deformed FeNi alloy.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on MnAl by Materials Project

MnAl is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Mn is bonded in a body-centered cubic geometry to eight equivalent Al atoms. All Mn–Al bond lengths are 2.55 Å. Al is bonded in a body-centered cubic geometry to eight equivalent Mn atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on MnAl by Materials Project

MnAl 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 Al atoms to form distorted MnMn4Al8 cuboctahedra that share corners with twelve equivalent MnMn4Al8 cuboctahedra, edges with eight equivalent MnMn4Al8 cuboctahedra, edges with sixteen equivalent AlMn8Al4 cuboctahedra, faces with eight equivalent AlMn8Al4 cuboctahedra, and faces with ten equivalent MnMn4Al8 cuboctahedra. All Mn–Mn bond lengths are 2.75 Å. All Mn–Al bond lengths are 2.62 Å. Al is bonded to eight equivalent Mn and four equivalent Al atoms to form AlMn8Al4 cuboctahedra that share corners with twelve equivalent AlMn8Al4 cuboctahedra, edges with eight equivalent AlMn8Al4 cuboctahedra, edges with sixteen equivalent MnMn4Al8 cuboctahedra, faces with eight equivalent MnMn4Al8 cuboctahedra, and faces with ten equivalent AlMn8Al4 cuboctahedra. All Al–Al bond lengths are 2.75 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Tm(MnAl)6 by Materials Project

Tm(MnAl)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Tm is bonded in a 8-coordinate geometry to twelve Mn and eight Al atoms. There are four shorter (3.19 Å) and eight longer (3.30 Å) Tm–Mn bond lengths. There are a spread of Tm–Al bond distances ranging from 2.88–3.02 Å. There are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a 12-coordinate geometry to two equivalent Tm, four Mn, and six Al atoms. There are two shorter (2.46 Å) and two longer (2.51 Å) Mn–Mn bond lengths. There are a spread of Mn–Al bond distances ranging from 2.52–2.62 Å. In the second Mn site, Mn is bonded to two equivalent Tm, four equivalent Mn, and six Al atoms to form a mixture of distorted corner, edge, and face-sharing MnTm2Mn4Al6 cuboctahedra. There are a spread of Mn–Al bond distances ranging from 2.61–2.64 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Tm, six Mn, and three Al atoms. There are one shorter (2.69 Å) and two longer (2.80 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 8-coordinate geometry to one Tm, six Mn, and three Al atoms. There are one shorter (2.80 Å) and two longer (3.01 Å) Al–Al bond lengths. In the third Al site, Al is bonded in a 12-coordinate geometry to two equivalent Tm, six Mn, and four Al atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Lu(MnAl)6 by Materials Project

Lu(MnAl)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Lu is bonded in a 8-coordinate geometry to twelve Mn and eight Al atoms. There are four shorter (3.18 Å) and eight longer (3.30 Å) Lu–Mn bond lengths. There are a spread of Lu–Al bond distances ranging from 2.88–3.04 Å. There are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a 12-coordinate geometry to two equivalent Lu, four Mn, and six Al atoms. There are two shorter (2.46 Å) and two longer (2.52 Å) Mn–Mn bond lengths. There are a spread of Mn–Al bond distances ranging from 2.52–2.62 Å. In the second Mn site, Mn is bonded to two equivalent Lu, four equivalent Mn, and six Al atoms to form a mixture of distorted edge, corner, and face-sharing MnLu2Mn4Al6 cuboctahedra. There are a spread of Mn–Al bond distances ranging from 2.61–2.64 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Lu, six Mn, and three Al atoms. There are one shorter (2.70 Å) and two longer (2.80 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 8-coordinate geometry to one Lu, six Mn, and one Al atom. The Al–Al bond length is 2.80 Å. In the third Al site, Al is bonded in a 12-coordinate geometry to two equivalent Lu, six Mn, and two equivalent Al atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Dy(MnAl)6 by Materials Project

Dy(MnAl)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Dy is bonded in a 8-coordinate geometry to twelve Mn and eight Al atoms. There are four shorter (3.18 Å) and eight longer (3.31 Å) Dy–Mn bond lengths. There are a spread of Dy–Al bond distances ranging from 2.91–3.06 Å. There are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a 12-coordinate geometry to two equivalent Dy, four Mn, and six Al atoms. There are two shorter (2.45 Å) and two longer (2.52 Å) Mn–Mn bond lengths. There are a spread of Mn–Al bond distances ranging from 2.52–2.63 Å. In the second Mn site, Mn is bonded to two equivalent Dy, four equivalent Mn, and six Al atoms to form a mixture of distorted corner, edge, and face-sharing MnDy2Mn4Al6 cuboctahedra. There are a spread of Mn–Al bond distances ranging from 2.61–2.68 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Dy, six Mn, and three Al atoms. There are one shorter (2.67 Å) and two longer (2.78 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 8-coordinate geometry to one Dy, six Mn, and three Al atoms. There are one shorter (2.82 Å) and two longer (2.99 Å) Al–Al bond lengths. In the third Al site, Al is bonded in a 12-coordinate geometry to two equivalent Dy, six Mn, and four Al atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ho(MnAl)6 by Materials Project

Ho(MnAl)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Ho is bonded in a 8-coordinate geometry to twelve Mn and eight Al atoms. There are four shorter (3.19 Å) and eight longer (3.32 Å) Ho–Mn bond lengths. There are a spread of Ho–Al bond distances ranging from 2.91–3.05 Å. There are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a 12-coordinate geometry to two equivalent Ho, four Mn, and six Al atoms. There are two shorter (2.47 Å) and two longer (2.53 Å) Mn–Mn bond lengths. There are a spread of Mn–Al bond distances ranging from 2.52–2.64 Å. In the second Mn site, Mn is bonded to two equivalent Ho, four equivalent Mn, and six Al atoms to form a mixture of distorted edge, corner, and face-sharing MnHo2Mn4Al6 cuboctahedra. There are a spread of Mn–Al bond distances ranging from 2.62–2.67 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Ho, six Mn, and three Al atoms. There are one shorter (2.71 Å) and two longer (2.80 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 8-coordinate geometry to one Ho, six Mn, and three Al atoms. There are one shorter (2.78 Å) and two longer (3.01 Å) Al–Al bond lengths. In the third Al site, Al is bonded in a 12-coordinate geometry to two equivalent Ho, six Mn, and four Al atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Er(MnAl)6 by Materials Project

Er(MnAl)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Er is bonded in a 8-coordinate geometry to twelve Mn and eight Al atoms. There are four shorter (3.18 Å) and eight longer (3.30 Å) Er–Mn bond lengths. There are a spread of Er–Al bond distances ranging from 2.89–3.05 Å. There are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a 12-coordinate geometry to two equivalent Er, four Mn, and six Al atoms. There are two shorter (2.46 Å) and two longer (2.52 Å) Mn–Mn bond lengths. There are a spread of Mn–Al bond distances ranging from 2.52–2.63 Å. In the second Mn site, Mn is bonded to two equivalent Er, four equivalent Mn, and six Al atoms to form a mixture of distorted face, edge, and corner-sharing MnEr2Mn4Al6 cuboctahedra. There are two shorter (2.61 Å) and four longer (2.64 Å) Mn–Al bond lengths. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Er, six Mn, and three Al atoms. There are one shorter (2.69 Å) and two longer (2.80 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 8-coordinate geometry to one Er, six Mn, and one Al atom. The Al–Al bond length is 2.78 Å. In the third Al site, Al is bonded in a 12-coordinate geometry to two equivalent Er, six Mn, and two equivalent Al atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Tb(MnAl)6 by Materials Project

Tb(MnAl)6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Tb is bonded in a 8-coordinate geometry to twelve Mn and eight Al atoms. There are four shorter (3.19 Å) and eight longer (3.32 Å) Tb–Mn bond lengths. There are a spread of Tb–Al bond distances ranging from 2.91–3.06 Å. There are two inequivalent Mn sites. In the first Mn site, Mn is bonded to two equivalent Tb, four Mn, and six Al atoms to form a mixture of distorted corner, edge, and face-sharing MnTb2Mn4Al6 cuboctahedra. There are two shorter (2.46 Å) and two longer (2.53 Å) Mn–Mn bond lengths. There are a spread of Mn–Al bond distances ranging from 2.52–2.64 Å. In the second Mn site, Mn is bonded to two equivalent Tb, four equivalent Mn, and six Al atoms to form a mixture of distorted corner, edge, and face-sharing MnTb2Mn4Al6 cuboctahedra. There are a spread of Mn–Al bond distances ranging from 2.61–2.67 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one Tb, six Mn, and three Al atoms. There are one shorter (2.70 Å) and two longer (2.79 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 8-coordinate geometry to one Tb, six Mn, and three Al atoms. There are one shorter (2.77 Å) and two longer (3.01 Å) Al–Al bond lengths. In the third Al site, Al is bonded in a 12-coordinate geometry to two equivalent Tb, six Mn, and four Al atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Giant room temperature anomalous Hall effect and tunable topology in a ferromagnetic topological semimetal Co 2 MnAl

Weyl semimetals exhibit unusual surface states and anomalous transport phenomena. It is hard to manipulate the band structure topology of specific Weyl materials. Topological transport phenomena usually appear at very low temperatures, which sets challenges for applications. In this work, we demonstrate the band topology modification via a weak magnetic field in a ferromagnetic Weyl semimetal candidate, Co 2 MnAl, at room temperature. We observe a tunable, giant anomalous Hall effect (AHE) induced by the transition involving Weyl points and nodal rings. The AHE conductivity is as large as that of a 3D quantum AHE, with the Hall angle (Θ H ) reaching a record value (tan Θ H = 0.21) at the room temperature among magnetic conductors. Furthermore, we propose a material recipe to generate large AHE by gaping nodal rings without requiring Weyl points. Our work reveals an intrinsically magnetic platform to explore the interplay between magnetic dynamics and topological physics for developing spintronic devices.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on MnAl(WO4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on MnAl(WO4)2 by Materials Project

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on MnAl(WO4)2 by Materials Project

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on MnAl(WO4)2 by Materials Project

36 MATERIALS SCIENCE↗

DOE OSTI2023

Orbital hybridisation effects in B2 phase Cr doped Co 2 MnAl

Here we investigate here the magnetic, transport, local structural and electronic properties of Co 2 Mn 1−x Cr x Al (x = 0, 0.05, 0.1 and 0.2). Our results show that all the compounds stabilise in B2 phase and are ferromagnets. The results reveal disorder at the structural and magnetic levels. X-ray absorption near edge structure (XANES) analysis reveal signature of antisite disorder between Mn and Al atoms with equal ratio. The electronic structure calculations suggest enhancement in the half metallicity, localisation of electrons at the Fermi level and an increment in density of states with doping. The combined results of electronic structure calculations and XANES studies suggest transfer of electrons to the Co site. The results of high temperature resistivity measurements suggest the conduction electrons are undergoing transition from delocalisation to weak localisation to activated behaviour with Cr doping. The extended x-ray absorption spectroscopic analysis shows that the local structure around Mn atom is different from the global structure as obtained from the x-ray diffraction results. The behaviour of the edge region is in line with the trend as obtained from the compositional analysis. We observe link between the hybridisation of 3d like states at the Mn, Cr sites with that at the Co site and the transport properties. This could help in understanding the unusual decrement in the lattice parameter with doping. These results reveal the role of local structure in understanding the physical properties of such systems.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Significance of the structural configuration of B2 disorder in Co and Ti based Heusler alloys

We investigate here structural (at local and global levels) and transport properties for 𝑋 2 ⁢MnAl (𝑋= Co and Ti). Additionally, the magnetic properties were also studied for Ti 2 ⁢MnAl. Our x-ray diffraction results show that both the compounds stabilize in B2 disordered phase with cubic structure of 𝑃⁢𝑚⁢$\overline{3}$⁢𝑚 space group. Further, the structural configuration of the above disordered phase for both the compounds was identified using combined studies of x-ray absorption spectroscopy and multiple scattering calculations at the transition metal 𝐾 edges. Upon such identification, in the case of Co 2 ⁢Mn 1−𝑦⁢ Cr 𝑦 ⁢Al (𝑦= 0, 0.05, 0.1, 0.2) with change in 𝑦, we are able to establish a better connection quantitatively between the inverse of Mn-Co bonds and peak in the temperature-dependent resistivity. This highlights the crucial importance of a detailed understanding of the nature of B2 disorder. In the case of 𝑦=0, in the temperature range of study, the resistivity is driven by the functional form associated with (a) three-dimensional enhanced electron-electron Coulomb interaction scattering mechanism and (b) an unconventional one-magnon process. For Ti 2 ⁢MnAl, the transport shows metallic glasslike behavior at high temperature, while at low temperature it follows both the Cote-Meisel's model and quantum correction model. In this compound, the magnetic studies suggest the formation of superparamagnetic clusters in the paramagnetic matrix at low temperatures. Our density functional theory results are in line with the transport and magnetic properties. In literature, the spin polarization percentage (𝑃) for 𝑋= Co in B2 disordered phase is 76%. However, the present results emphasize the fact that in B2 disordered phase, the value of 𝑃 can range from 90% to 71% depending on the structural configuration introduced by swapping of the atomic positions of Mn and Al. For the compound under study, the value of percentage spin polarization obtained ranges between 82% to 85%. In addition, we also identify the origin of the difference in the shape of the Mn 3⁢𝑑 density of states for both the alloys. In conclusion, our results for 𝑋= Co alloy highlights the importance of identifying the specific structural configuration associated with a particular disorder category especially in the estimation of 𝑇 𝑐 and 𝑃 and for 𝑋= Ti, the physical properties can be tuned by varying the position of 𝐸 𝐹 and thereby its utilization in device applications.

36 MATERIALS SCIENCE↗