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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.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Influence of Non-magnetic Ti{sup 4+} Ion Doping at Mn Site on Structural, Magnetic, and Magnetocaloric Properties of La{sub 0.5}Pr{sub 0.2}Sr{sub 0.3}Mn{sub 1−x}Ti{sub x}O{sub 3} Manganites (x = 0.0 and 0.1)

Polycrystalline perovskite AMn{sub 1−x}TiO{sub 3} with A = La{sub 0.5}Pr{sub 0.2}Sr{sub 0.3} (x = 0.0 and 0.1) have been prepared using solid-state reaction method. X-ray powder diffraction and Rietveld refinement revealed that all samples crystallize in a rhombohedral structure with space group R 3-bar c From M–T curve, we determined the Curie temperature, where the magnetization value decreases abruptly. The Curie temperature (T{sub C}) decreases from 280 to 123 K when the percentage of Ti increases to 10%. The values of the magnetization M(H) decrease when increasing the Ti content. Moreover, the magnetocaloric effect (MCE) was estimated in terms of isothermal entropy change (−ΔS{sub M}) using the M(T, μ{sub 0}H) data and employing the thermodynamic Maxwell equation. In addition, using a phenomenological model, we determine magnetocaloric effect from the calculation of magnetization as a function of temperature under different external magnetic fields. Also, we can determine the relative cooling power (RCP) and the specific heat which varies from 2.803 to 7.354 J/(kg/K) for the undoped sample from M(T, μ{sub 0}H) data at different magnetic fields theoretically.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A family of rare earth uranium oxides, RE{sub 6}UO{sub 12-δ}, (RE = Rare Earth). Synthesis, structure and magnetic behavior

Highlights: • A series of rare earth urinates, RE{sub 6}UO{sub 12}, were synthesized using the solid state method. • The crystal structures of RE{sub 6}UO{sub 12} were refined using the Rietveld method. • Magnetic properties were measured and AF ordering was observed in RE = Gd, Tb, Dy. - Abstract: A series of rare earth uranates, RE{sub 6}UO{sub 12-δ} (RE = La, Nd, Sm – Dy, Er and Yb), were synthesized via the solid state method and their structures were determined using the Rietveld method. These compounds crystallize in the rhombohedral space group R-3H with the lattice parameters a = 10.47005(3) Å and c = 9.98034(3) Å for the La analogue. The temperature and field dependent magnetization are reported for each analogue. Antiferromagnetic ordering is observed for RE = Gd, Tb, and Dy with Néel temperatures of 2.1 K, 5.8 K, and 2.8 K, respectively. Magnetic measurements on the La{sub 6}UO{sub 12} analogue indicate the presence of some U{sup 5+}, and therefore, oxygen vacancies in the structure. The variability of the U valence is examined.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Magnets, Magnets, Magnets!

Explore the source record for details and available documents.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Magnetic Switching in Monolayer 2D Diluted Magnetic Semiconductors via Spin‐to‐Spin Conversion

Abstract The integration of 2D van der Waals (vdW) magnets with topological insulators or heavy metals holds great potential for realizing next‐generation spintronic memory devices. However, achieving high‐efficiency spin–orbit torque (SOT) switching of monolayer vdW magnets at room temperature poses a significant challenge, particularly without an external magnetic field. Here, it is shown field‐free, deterministic, and nonvolatile SOT switching of perpendicular magnetization in the monolayer, diluted magnetic semiconductor (DMS), Fe‐doped MoS 2 (Fe:MoS 2 ) at up to 380 K with a current density of ≈7 × 10 4 A cm −2 . The in situ doping of Fe into monolayer MoS 2 via chemical vapor deposition and the geometry‐induced strain in the crystal break the rotational switching symmetry in Fe:MoS 2 , promoting field‐free SOT switching by generating out‐of‐plane spins via spin‐to‐spin conversion. An apparent anomalous Hall effect (AHE) loop shift at a zero in‐plane magnetic field verifies the existence of z spins in Fe:MoS 2 , inducing an antidamping‐like torque that facilitates field‐free SOT switching. This field‐free SOT application using a 2D ferromagnetic monolayer provides a new pathway for developing highly power‐efficient spintronic memory devices.

Chen, Siwei [Department of Mechanical Engineering ↗
DOE OSTI2021

In-situ magnetic alignment model for additive manufacturing of anisotropic bonded magnets

In this work, we report a mathematical framework which predicts the degree of alignment (DoA) in an in-situ aligned additively manufactured 3D printed bonded magnets. A multiphysics model is developed which couples the harmonious interactions of magnetic particles in a viscous flowing polymer under the presence of an external magnetic field. The hydrodynamic fluid-particle interaction is paired with the magnetophoretic force to predict the particle trajectory and distribution during extrusion through a 3D printer nozzle. Succeeding the force balance, a magnetohydrodynamic torque equilibrium analysis is performed to predict the net-orientation of the magnetic particles as a function of the applied field strength, viscous forces, and particle-to-particle interactions (P2P). Experimental validation of the DoA predictions is performed using 65 vol% Nd-Fe-B+Sm-Fe-N in Nylon12 (DoA exp = 0.620 and DoA theory = 0.686) and 15 vol% Sm-Co in PLA (DoA exp = 0.830 and DoA theory = 0.863). A parametric analysis is performed to analyze the effect of operating and design parameters like alignment field strength, magnetic loading fraction, extrusion load, and particle size. The model predicts a competing behavior between particle-fluid and particle-particle interactions under the presence of an applied field. Lastly, the model provides a framework to efficiently predict the DoA in tandem with a functionalized-magnetic 3D printer and allows the user to adjust the operating parameters according to the desired DoA.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Direct and indirect measurements of the magnetic and magnetocaloric properties of Ni 0.895 Cr 0.105 MnGe 1.05 melt-spun ribbons in high magnetic fields

We report the magnetic and magnetocaloric properties of rapidly solidified Ni 0.895 Cr 0.105 MnGe 1.05 melt-spun ribbons studied by both direct (adiabatic temperature change) and indirect (isothermal magnetic entropy change) methods in intermediate and high magnetic fields up to 10 T. The maximum values of the adiabatic temperature changes (ΔT ad ) and magnetic entropy changes ( Δ S M ) were found to be ~2.6 K (µ o H = 10 T) and 4.4 J kg -1 K -1 (µ o ΔH = 5 T), respectively, near the Curie temperature (T C ). The ΔT ad curves and magnetization isotherms were found to be completely reversible, which indicates the high degree of reversibility of the MCEs in this system. A large temperature span (of about 61 K) and a non-saturating behavior of ΔT ad were observed at magnetic fields up to 10 T. The adiabatic temperature change was found to be a linear function of (µ o H) 2/3 near T C , in accordance with the Landau theory of phase transitions.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Interfacial magnetic vortex formation in exchange-coupled hard-soft magnetic bilayers

The exchange coupling between a hard magnetic layer MnBi and a soft magnetic layer Co-Fe has been found to significantly improve the maximum energy product. In this work, the spin structure of exchange coupled MnBi:Co-Fe bilayers is experimentally investigated by X-ray magnetic circular dichroism (XMCD) and polarized neutron reflectometry (PNR). We find that the out-of-plane magnetization reversal process of the MnBi:Co-Fe bilayer structure involves formation of a curling-type twisting of the magnetization in the film plane at low or intermediate reversal fields. Additionally, micromagnetic simulations are further performed to provide a detailed view of the spins at the curling center. Reminiscent of chiral spin structures known as spin bobbers, this curling in the exchange-coupled hard-soft magnetic bilayers is a new type of skyrmionic spin structure and worth further investigation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Statistical description of coalescing magnetic islands via magnetic reconnection

The physical picture of interacting magnetic islands provides a useful paradigm for certain plasma dynamics in a variety of physical environments, such as the solar corona, the heliosheath and the Earth's magnetosphere. In this work, we derive an island kinetic equation to describe the evolution of the island distribution function (in area and in flux of islands) subject to a collisional integral designed to account for the role of magnetic reconnection during island mergers. This equation is used to study the inverse transfer of magnetic energy through the coalescence of magnetic islands in two dimensions. We solve our island kinetic equation numerically for three different types of initial distribution: Dirac delta, Gaussian and power-law distributions. The time evolution of several key quantities is found to agree well with our analytical predictions: magnetic energy decays as $\tilde {t}^{-1}$ , the number of islands decreases as $\tilde {t}^{-1}$ and the averaged area of islands grows as $\tilde {t}$ , where $\tilde {t}$ is the time normalised to the characteristic reconnection time scale of islands. General properties of the distribution function and the magnetic energy spectrum are also studied. Finally, we discuss the underlying connection of our island-merger models to the (self-similar) decay of magnetohydrodynamic turbulence.

Physics↗
DOE OSTI2023

Validation of magnetized gas-jet experiments to investigate the effects of an external magnetic field on laser-plasma instabilities

Laser-plasma instabilities (LPI) play a detrimental role in energy coupling to the target in inertial confinement fusion (ICF). The recent development of applied strong magnetic fields for use in ICF and laboratory astrophysics experiments has opened opportunities to investigate the role of external magnetic fields on LPIs. Recent numerical studies have shown that stimulated Raman scattering (SRS) can be mitigated by external magnetic fields in the kinetic regime of the instability and warrant systematic experimental studies to validate modelling. To this end, we design experiments at the OMEGA-EP laser facility to investigate the effect of an external perpendicular B-field of 5–30 T on the backscattered light spectrum from a gas-jet target. We present measurements from a proof-of-principle experiment, where the backward-SRS (BSRS) is in the kinetic regime, for which the magnetization is expected to produce the greatest effects on instability growth. New simulations motivated by this experiment are used to inform the proposal of an upgraded experimental design. Our simulation predictions show that the new design is suited to experimentally demonstrating BSRS mitigation by an external magnetic field, despite the magnetization effects on the hydrodynamics, as well as the inherent temporal and spatial variations in plasma conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

A Polar Magnetic and Insulating Double Corundum Oxide: Mn2MnSbO6 with Ordered Mn(II) and Mn(III) Ions

A new magnetic insulator Mn2MnSbO6 with a polar crystal structure and an ordered Mn2+ and Mn3+ arrangement was synthesized under a high pressure of 7.5 GPa and 1300 degrees C. The crystal structure of Mn2MnSbO6, investigated by synchrotron powder X-ray diffraction, was found to be isomorphous with that of Ni3TeO6-type, space group R3. The non-centrosymmetric structure was confirmed by the second-harmonic generation measurements. The X-ray absorption near-edge spectroscopy measurement confirmed the nominal oxidation states of Mn22+Mn3+SbO6. Magnetic measurements indicate that Mn2MnSbO6 orders antiferromagnetically below 44 K and undergoes a field-induced spin-flop transition at 5 K. First-principles calculations indicate an antiferromagnetic ground state with up/up/up/down/down/down (uuuddd) spin configuration of the six crystallographically unique Mn ions in the c-axis doubled magnetic structure. The density functional theory calculations also substantiate the experimentally observed charge ordering of the Mn2+/Mn3+ ions and the insulating behavior due to a bandgap of 0.52 eV. To the best of our knowledge, this is the first double corundum oxide containing Jahn-Teller active Mn3+ ions.

Feng, Hai L.↗
DOE OSTI2019

Multireference Ab Initio Studies of Magnetic Properties of Terbium-Based Single-Molecule Magnets

Here, we explore how different chemical environments influence magnetic properties of terbium(III) (Tb)-based single-molecule magnets (SMMs), using first-principles relativistic multireference methods. Recent experiments showed that Tb-based SMMs can have exceptionally large magnetic anisotropy and that they can be used for experimental realization of quantum information applications, with a judicious choice of chemical environment. Here, we perform complete active space self-consistent field calculations including relativistic spin–orbit interaction for representative Tb-based SMMs such as TbPc 2 and TbPcNc in three charge states. We calculate the low-energy electronic structure from which we compute the Tb crystal-field (CF) parameters and construct an effective pseudospin Hamiltonian. Our calculations show that the ligand type and fine points of molecular geometry do not affect the gap between the ground-state and first-excited doublets, whereas the latter varies weakly with oxidation number. On the other hand, higher-energy levels have a strong dependence on all these characteristics. For neutral TbPc 2 and TbPcNc molecules, the Tb magnetic moment and ligand spin are parallel to each other and the coupling strength between them does not depend much on the ligand type and details of the atomic structure. However, ligand distortion and molecular symmetry play a crucial role in transverse CF parameters which lead to tunnel splitting. The tunnel splitting induces quantum tunneling of magnetization by itself or by combining with other processes. Our results provide insights into the mechanisms of magnetization relaxation in the representative Tb-based SMMs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗