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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Strain-modulated helimagnetism and emergent magnetic phase diagrams in highly crystalline MnP nanorod films

Here, we explore strain-modulated helimagnetism in highly crystalline MnP nanorod films grown on Si(100) substrates using molecular beam epitaxy. The strained MnP film exhibits a paramagnetic to ferromagnetic (FM) phase transition at $T_C$ ~ 279 K, and the FM to helical phase transition at $T_N$ ~ 110 K. The value of $T_N$ is greater than $T_N$ ~ 47K for the MnP single crystal, indicating strong strain-modulated helimagnetic states in the MnP nanorod film. The presence of significant thermal hysteresis in the helical phase indicates the coexistence of competing magnetic interactions, leading to the first-order metamagnetic transition. Similar to its single-crystal counterpart, an anisotropic magnetic effect is observed in the MnP film, which is independently confirmed by magnetic hysteresis loop and radio-frequency transverse susceptibility (TS) measurements. The evolution of the screw to the cone and fan phases is precisely tracked from magnetization vs magnetic field/temperature measurements. The temperature dependence of the anisotropy fields, extracted from the TS spectra, yields further insight into the competing nature of the magnetic phases. Unfolding of the different helical phases at $\textit{T}$ < 120 K (~$T_N$) is analyzed by the temperature- and field-dependent magnetic entropy change. Based on these findings, the comprehensive magnetic phase diagrams of the MnP nanorod film are constructed for both the in-plane and out of plane magnetic field directions, revealing emergent strain/dimensionality-driven helical magnetic features that are absent in the magnetic phase diagram of the MnP single crystal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

MnP Films with Desired Magnetic, Magnetocaloric, and Thermoelectric Properties for a Perspective Magneto-Thermo-Electric Cooling Device

A new magneto-thermo-electric cooling device (MTECD) comprising a central magnetocaloric (MC) material (e.g., Gd) sandwiched by two thermoelectric (TE) materials (e.g., MnP) is proposed. The presence of the TE materials in the MTECD guides the heat flow direction and enhances heat pulsation. Here in this case, the usage of a ferromagnetic TE material that combines large TE with small MC properties within a similar temperature region can enhance the magnetic flux density and heat exchange efficiency. Herein, it is shown that MnP nanorod-structured films with desired magnetic, MC, and TE properties are very promising for use in MTECDs. The films are grown on Si substrates at 300, 400, and 500 °C using molecular beam epitaxy. The 400 °C sample shows a desired TE and MC combination. A large power factor of 24.06 μW m -1 K -2 is achieved at room temperature. In this temperature region, the film exhibits a small MC effect (-ΔS M ≈0.64 J kg -1 K and ΔT ad ≈0.3 K at μ 0 H = 2 T) but ferromagnetism that gives rise to the enhanced MC effect of the central MC material. These properties can enable the MTECD to operate at high frequency.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(MnP)2 by Materials Project

Cs(MnP)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Cs1+ is bonded in a distorted body-centered cubic geometry to eight equivalent P+2.50- atoms. All Cs–P bond lengths are 3.66 Å. Mn2+ is bonded to four equivalent P+2.50- atoms to form a mixture of edge and corner-sharing MnP4 tetrahedra. All Mn–P bond lengths are 2.28 Å. P+2.50- is bonded in a 4-coordinate geometry to four equivalent Cs1+ and four equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnP by Materials Project

MnP is Modderite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Mn2+ is bonded to six equivalent P2- atoms to form a mixture of distorted corner, edge, and face-sharing MnP6 octahedra. The corner-sharing octahedra tilt angles range from 44–56°. There are a spread of Mn–P bond distances ranging from 2.26–2.38 Å. P2- is bonded in a 6-coordinate geometry to six equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(MnP)2 by Materials Project

Ca(MnP)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent P3- atoms to form CaP6 octahedra that share corners with twelve equivalent MnP4 tetrahedra, edges with six equivalent CaP6 octahedra, and edges with six equivalent MnP4 tetrahedra. All Ca–P bond lengths are 2.91 Å. Mn2+ is bonded to four equivalent P3- atoms to form MnP4 tetrahedra that share corners with six equivalent CaP6 octahedra, corners with six equivalent MnP4 tetrahedra, edges with three equivalent CaP6 octahedra, and edges with three equivalent MnP4 tetrahedra. The corner-sharing octahedra tilt angles range from 24–49°. There are one shorter (2.27 Å) and three longer (2.30 Å) Mn–P bond lengths. P3- is bonded in a 7-coordinate geometry to three equivalent Ca2+ and four equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnP by Materials Project

MnP is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mn2+ is bonded to six equivalent P2- atoms to form a mixture of corner, edge, and face-sharing MnP6 octahedra. The corner-sharing octahedral tilt angles are 48°. All Mn–P bond lengths are 2.35 Å. P2- is bonded in a 6-coordinate geometry to six equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnP by Materials Project

MnP is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mn2+ is bonded to four equivalent P2- atoms to form corner-sharing MnP4 tetrahedra. All Mn–P bond lengths are 2.28 Å. P2- is bonded to four equivalent Mn2+ atoms to form corner-sharing PMn4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba(MnP)2 by Materials Project

BaMn2P2 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ba2+ is bonded in a body-centered cubic geometry to eight equivalent P3- atoms. All Ba–P bond lengths are 3.35 Å. Mn2+ is bonded to four equivalent P3- atoms to form a mixture of corner and edge-sharing MnP4 tetrahedra. All Mn–P bond lengths are 2.28 Å. P3- is bonded in a 4-coordinate geometry to four equivalent Ba2+ and four equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(MnP)2 by Materials Project

SrMn2P2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Sr2+ is bonded to six equivalent P3- atoms to form distorted SrP6 octahedra that share corners with twelve equivalent MnP4 tetrahedra, edges with six equivalent SrP6 octahedra, and edges with six equivalent MnP4 tetrahedra. All Sr–P bond lengths are 3.06 Å. Mn2+ is bonded to four equivalent P3- atoms to form MnP4 tetrahedra that share corners with six equivalent SrP6 octahedra, corners with six equivalent MnP4 tetrahedra, edges with three equivalent SrP6 octahedra, and edges with three equivalent MnP4 tetrahedra. The corner-sharing octahedra tilt angles range from 27–47°. There are one shorter (2.27 Å) and three longer (2.32 Å) Mn–P bond lengths. P3- is bonded in a 7-coordinate geometry to three equivalent Sr2+ and four equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Optimal production of Phanerochaete chrysosporium manganese peroxidases and Trametes sp. C30 laccase hybrid Lac131 in Aspergillus niger for lignin bioconversion

Background Incorporating the production of related ligninolytic enzymes into industrial filamentous fungus Aspergillus niger will enhance the bioconversion of lignocelluloses to various chemical products. Results In this study, transgenic expression of Phanerochaete chrysosporium manganese peroxidases (mnps) and Trametes sp. C30 laccase hybrid Lac131 (lac131) were examined and optimized in A. niger 11414 prtT∆ strain. Five mnps (mnp1, mnp2, mnp3, mnp4, and mnp5) and lac131 genes were expressed separately or in combination. The transgenic strain containing the entire mnp2 genomic coding sequence (gmnp2) exhibited the highest mnP activity among the five mnp over-expression strains in the modified minimal medium (mMM) with addition of 5 g/L bovine hemoglobin (bHg). We examined the effects of hemin and bHg on mnP production in the gmnp2 strain cultures and found that at least 1 g/L bHg was required, while hemin was not. Culture conditions for mnP production were further optimized for the gmnp2 strain and the highest mnP activities were detected in the cultures grown at 25 °C and 200 rpm with an initial pH of 4.5. Effects of soy protein, skim milk, and bovine serum albumin on mnP production were investigated; 5 g/L of soy proteins or skim milk had comparable effects to 2.5 g/L bHg, while cultures with bovine serum albumin had diminished mnP activity. Disruption of both prtT and vsm1 substantially augmented the mnP production and its activity reached 575 U/L. Trametes sp. C30 laccase hybrid lac131 was strongly expressed in either A. niger gmnp2 (1975 U/L) or 11414prtT∆ (3895 U/L) strain. Both mnP and laccase in the culture supernatants effectively decolorized selected phenolic compounds (dyes) and cleaved tagged model lignin dimers. Conclusion The mnP was successfully produced in A. niger by optimizing the culture conditions and host strain. Co-expression of all four mnp genes in the same expression host by multiplex CRISPR will lead to the mnP production reaching levels comparable to P. chrysosporium, while only requiring 36 h at 25 °C. The Lac131 activity in transgenic A. niger strain is 4- to 7-times higher than that in previous studies. Co-production of mnP and laccase in A. niger will enhance the lignin bioconversion efficiency.

Aspergillus niger↗
DOE OSTI2024

Magnetic functionalization and catalytic behavior of magnetic nanoparticles during laser photochemical graphitization of polyimide

We report laser-assisted photochemical graphitization of polyimides (PIs) into functional magnetic nanocomposites using laser irradiation of PI in the presence of magnetite nanoparticles (MNPs). PI Kapton sheets covered with MNP were photochemically treated under ambient conditions using a picosecond pulsed laser (1064 nm) to obtain an electrically conductive material. Scanning electron microscopy of the treated material revealed a layered magnetic nanoparticle/graphite (MNP/graphite) nanocomposite structure. Four probe conductivity measurements indicated that the nanocomposite has an electrical conductivity of 1550 ± 60 S/m. Superconducting quantum interference device magnetometer-based magnetic characterization of the treated material revealed an anisotropic ferromagnetic response in the MNP/graphite nanocomposite compared to the isotropic response of MNP. Raman spectroscopy of the MNP/graphite nanocomposite revealed a fourfold improvement in graphitization, suppression in disorder, and decreased nitrogenous impurities compared to the graphitic material obtained from laser treatment of just PI sheets. X-ray photoelectron spectroscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy were used to delineate the phase transformations of MNP during the formation of MNP/graphite nanocomposite. Post-mortem characterization indicates a possible photocatalytic effect of MNP during MNP/graphite nanocomposite formation. Under laser irradiation, MNP transformed from the initial Fe 3 O 4 phase to γ-Fe 2 O 3 and Fe 5 C 2 phases and acted as nucleation spots to catalyze the graphitization process of PI.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Single Grid Error Estimation for Neutron Transport Solvers

The method of nearby problems (MNP) is a solution verification technique that does not require the use of multiple spatial grids. To estimate spatial discretization error without requiring a high-fidelity spatial grid, an analytical curve fit is interpolated from the numerical solution. The residual between the curve fit solution and numerical solution is calculated and added as an additional source term to the governing equation. The nearby solution is estimated using the updated source term and boundary conditions to remain consistent with the curve fit interpolation. The nearby solution can be compared to the curve fit solution as a discretization error estimation while using a single spatial grid. Without the use of higher fidelity spatial grids, the MNP is able to approximate the spatial discretization error, a facet of solution verification. The application of the method of nearby problems is presented for one- and two-dimensional neutron transport problems for both fixed source and criticality problems on the spatial variable. The fixed source results demonstrate the effectiveness of nearby problems for spatial error identification using the discrete ordinates method. Criticality results are shown to identify area of high spatial error for the C5G7 problem as well as for the discrete ordinates solver. A novel approach of combining the capabilities of Monte Carlo with the discrete ordinates nearby problems is presented for one- and two-dimensional fixed source problems. In conclusion, the MNP demonstrates its effectiveness at identifying spatial error on a single structured grid with a wide variety of neutron transport problems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Pressure Variation of Magnetism in Chromium and Manganese Mono-Pnictide Superconductors

The transition-metal pnictide system MX (M = transition metal and X = P, As, and Sb) has been studied for several decades because those materials show rich magnetic phase diagrams. Since the recent discovery of unconventional superconductivity in isomorphic CrAs and MnP under high pressures, physical properties of the two materials have been investigated intensively as a function of pressure. In particular, since both materials exhibit quantum critical behavior with applied pressure, magnetic fluctuations are considered to be the key to the superconducting pairing mechanism. Interestingly, both materials were found to show double helical spin structures in the vicinity of the pressure-induced superconducting phase. Here, a review is given on the magnetic properties of MX, including our high-pressure neutron scattering studies performed in CrAs and MnP. We also give a brief review on technical developments of high pressure cells for neutron diffraction, including the high pressure cells used for our high pressure measurements in CrAs and MnP.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Measuring the Interfacial Chemistry of Micro- and Nano-Plastics Using Matrix Assisted Laser Desorption Ionization

Micro- and nano-plastics (MNPs) pose a significant hazard to both environmental and human health due to their complex interfacial interactions with their surroundings, however there is a lack of techniques available to study the composition of MNPs at their surface. To fill this gap, representative MNPs were coated with matrix that enabled detection via matrix-assisted laser desorption ionization mass spectrometry (MALDI), a technique that has been shown to be surface specific but had not been applied to MNPs previously. Three different coating techniques were tested; evaporation and condensation, drop-casting, and mixed nebulization. Mixed nebulization provided the best balance of results, which was a strong MALDI signal in combination with even coating on the MNP surface from MNPs ≥20 µm. This work provides a new technique for the measurement of MNP surface composition that will help advance the field and enable more thorough studies of the chemical transformations that MNPs undergo in the environment.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Intergranular Spin Dependent Tunneling Dominated Magnetoresistance in Helimagnetic Manganese Phosphide Thin Films

Helical magnets are emerging as a novel class of materials for spintronics and sensor applications; however, research on their charge- and spin-transport properties in a thin film form is less explored. Herein, we report the temperature and magnetic field-dependent charge transport properties of a highly crystalline MnP nanorod thin film over a wide temperature range (2 K < T < 350 K). The MnP nanorod films of ~100 nm thickness were grown on Si substrates at 500 °C using molecular beam epitaxy. The temperature-dependent resistivity ρ(T) data exhibit a metallic behavior (dρ/dT > 0) over the entire measured temperature range. However, large negative magnetoresistance (Δρ/ρ) of up to 12% is observed below ~50 K at which the system enters a stable helical (screw) magnetic state. In this temperature regime, the Δρ(H)/ρ(0) dependence also shows a magnetic field-manipulated CONE + FAN phase coexistence. The observed magnetoresistance is dominantly governed by the intergranular spin dependent tunneling mechanism. These findings pinpoint a correlation between the transport and magnetism in this helimagnetic system.

36 MATERIALS SCIENCE↗