Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “MAGNETIC MATERIALS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Anomalous transport due to Weyl fermions in the chiral antiferromagnets Mn 3 X, X = Sn, Ge

The recent discoveries of strikingly large zero-field Hall and Nernst effects in antiferromagnets Mn 3 X(X = Sn, Ge) have brought the study of magnetic topological states to the forefront of condensed matter research and technological innovation. These effects are considered fingerprints of Weyl nodes residing near the Fermi energy, promoting Mn 3 X(X = Sn, Ge) as a fascinating platform to explore the elusive magnetic Weyl fermions. In this review, we provide recent updates on the insights drawn from experimental and theoretical studies of Mn 3 X(X = Sn, Ge) by combining previous reports with our new, comprehensive set of transport measurements of high-quality Mn 3 Sn and Mn 3 Ge single crystals. In particular, we report magnetotransport signatures specific to chiral anomalies in Mn 3 Ge and planar Hall effect in Mn 3 Sn, which have not yet been found in earlier studies. The results summarized here indicate the essential role of magnetic Weyl fermions in producing the large transverse responses in the absence of magnetization.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Synthesis, magnetization, and heat capacity of triangular lattice materials NaErSe 2 and KErSe 2

In this paper we report the synthesis, magnetization, and heat capacity of the frustrated magnets A ErSe 2 ( A = Na , K ) which contain perfect triangular lattices of Er 3 + . The magnetization data suggests no long-range magnetic order exists in A ErSe 2 ( A = Na , K ), which is consistent with the heat capacity measurements. Large anisotropy is observed between the magnetization within the a b plane and along the c axis of both compounds. When the magnetic field is applied along the a b plane, anomalies are observed at 1.8 μ B in NaErSe 2 at 0.2 T and 2.1 μ B in KErSe 2 at 0.18 T. Unlike NaErSe 2 , a plateaulike field-induced metamagnetic transition is observed for H ∥ c below 1 K in KErSe 2 . Two broad peaks are observed in the heat capacity below 10 K indicating possible crystal electric field (CEF) effects and magnetic entropy released under different magnetic fields. All results indicate that A ErSe 2 are strongly anisotropic, frustrated magnets with field-induced transition at low temperature. The lack of signatures for long-range magnetic order implies that these materials are candidates for hosting a quantum spin liquid ground state.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Competition Between Antiferromagnetism and Ferromagnetism in Sr 2 RuO 4 Probed by Mn and Co Doping

Spin-triplet superconductivity in Sr 2 RuO 4 has attracted enormous interest. Like other unconventional superconductors, superconductivity in Sr 2 RuO 4 is in close proximity to magnetic instability. Undoped Sr 2 RuO 4 exhibits incommensurate antiferromagnetic (AFM) fluctuations, which can evolve into static, short-range AFM order via Ti doping. Moreover, weak ferromagnetic (FM) coupling in Sr 2 RuO 4 has also been suggested by NMR/neutron scattering experiments and studies on Ca 2–x Sr xR uO 4 and Sr 2–y La y RuO 4 , implying orbital dependent magnetism. We report bulk static, short-range FM order in Sr 2 RuO 4 triggered by <2% Co doping, showing superconductivity in Sr 2 RuO 4 is much closer to FM instability than previously reported in Ca 2–x Sr x RuO 4 . We also find Mn doping can effectively establish incommensurate AFM order, with TN ~ 50 K for 3% Mn doping. These new results place Sr 2 RuO 4 in a unique situation where superconductivity lies directly on the borderline of two distinct magnetic states, highlighting the important role of competing magnetic fluctuations in determining superconducting properties of Sr 2 RuO 4 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

System and method for manipulating domain pinning and reversal in ferromagnetic materials

A method for manipulating domain pinning and reversal in a ferromagnetic material comprises applying an external magnetic field to a uniaxial ferromagnetic material comprising a plurality of magnetic domains, where each domain has an easy axis oriented along a predetermined direction. The external magnetic field is applied transverse to the predetermined direction and at a predetermined temperature. The strength of the magnetic field is varied at the predetermined temperature, thereby isothermally regulating pinning of the domains. A magnetic storage device for controlling domain dynamics includes a magnetic hard disk comprising a uniaxial ferromagnetic material, a magnetic recording head including a first magnet, and a second magnet. The ferromagnetic material includes a plurality of magnetic domains each having an easy axis oriented along a predetermined direction. The second magnet is positioned adjacent to the magnetic hard disk and is configured to apply a magnetic field transverse to the predetermined direction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Static Magnetic Properties of AL800 Garnet Material

A second harmonic tunable RF cavity is being devel-oped for the Fermilab Booster. This device, which prom-ises reduction of the particle beam loss at the injection, transition, and extraction stages, employs perpendicularly biased garnet material for frequency tuning. The required range of the tuning is significantly wider than in previously built and tested tunable RF devices. As a result, the mag-netic field in the garnet comes fairly close to the gyromag-netic resonance line at the lower end of the frequency range. The chosen design concept of a tuner for the cavity cannot ensure uniform magnetic field in the garnet mate-rial; thus, it is important to know the static magnetic prop-erties of the material to avoid significant increase in the lo-cal RF loss power density. This report summarizes studies performed at Fermilab to understand variations in the mag-netic properties of the AL800 garnet material used to build the tuner of the cavity.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Perpendicular magnetic anisotropy of amorphous [CoSiB/Pt]{sub N} thin films

Materials with perpendicular magnetic anisotropy (PMA) have been intensively studied for high-density nonvolatile memory such as spin-transfer-torque magnetic random access memory with low switching current density and high thermal stability. Compared with crystalline PMA multilayers, considerable works have been done on amorphous PMA multilayers because the amorphous materials are expected to have lower pinning site density as well as smaller domain wall width. This study is an overview of the PMA properties of amorphous [CoSiB/Pt]{sub N} multilayers with varying N, where the energy contribution is changed from domain wall energy to magnetostatic energy around N = 6. By measuring the field-induced domain wall motion, we obtain the creep exponent of μ = 1/4. These results in the amorphous PMA multilayers of [CoSiB/Pt]{sub N} demonstrate possible potential as a free layer for PMA-based memory devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Critical Magnetic Field Determination of Superconducting Materials

Superconducting RF technology is becoming more and more important. With some recent cavity test results showing close to or even higher than the critical magnetic field of 170-180 mT that had been considered a limit, it is very important to develop a way to correctly measure the critical magnetic field (H{sup RF}{sub c}) of superconductors in the RF regime. Using a 11.4 GHz, 50-MW, <1 {mu}s, pulsed power source and a TE013-like mode copper cavity, we have been measuring critical magnetic fields of superconductors for accelerator cavity applications. This device can eliminate both thermal and field emission effects due to a short pulse and no electric field at the sample surface. A model of the system is presented in this paper along with a discussion of preliminary experimental data.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

High-temperature concomitant metal-insulator and spin-reorientation transitions in a compressed nodal-line ferrimagnet Mn 3 Si 2 Te 6

Symmetry-protected band degeneracy, coupled with a magnetic order, is the key to realizing novel magnetoelectric phenomena in topological magnets. While the spin-polarized nodal states have been identified to introduce extremely-sensitive electronic responses to the magnetic states, their possible role in determining magnetic ground states has remained elusive. Here, taking external pressure as a control knob, we show that a metal-insulator transition, a spin-reorientation transition, and a structural modification occur concomitantly when the nodal-line state crosses the Fermi level in a ferrimagnetic semiconductor Mn 3 Si 2 Te 6 . These unique pressure-driven magnetic and electronic transitions, associated with the dome-shaped Tc variation up to nearly room temperature, originate from the interplay between the spin-orbit coupling of the nodal-line state and magnetic frustration of localized spins. Our findings highlight that the nodal-line states, isolated from other trivial states, can facilitate strongly tunable magnetic properties in topological magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Process for recycling rare earth magnets

A method to separate rare earth material from a rare earth magnet. At least one embodiment comprises a method that heats a provided rare earth magnet to at least 600° C. whereby the rare earth magnet absorbs a dry gas. Separated rare earth materials are created. Magnetic rare earth materials are produced from the separated rare earth materials.

Tripathy, Prahbat K.↗
DOE OSTI2014

Low-temperature solvothermal synthesis of EuS hollow microspheres

Graphical abstract: Synthesis of EuS hollow microspheres at low-temperature via solvothermal method for the first time. - Highlights: • We adopt an improved method to synthesise the (Phen)Eu(Et{sub 2}CNS{sub 2}){sub 3} in deionized water. • We have successfully synthesised the EuS hollow microsphere at 230 °C in acetonitrile. • The price of acetonitrile is more inexpensive, so the price of preparation was reduced. - Abstract: EuS crystals are synthesized by low-temperature solvothermal decomposition of the single source precursor complex (Phen)Eu(Et{sub 2}CNS{sub 2}){sub 3} in acetonitrile. X-ray powder diffraction, scanning electron microscopy, granulocyte diameter statistical analysis, surface energy-dispersive X-ray spectroscopy analysis, and UV–vis absorption spectroscopy are used to characterize the structure and properties of the obtained EuS crystals. The results show that the formed EuS crystals are uniform hollow microspheres with a typical cubic phase structure of rock salt and the average particle size of 2.01 μm. The mechanisms for the thermal decomposition of the precursor complex and the formation of the EuS hollow microspheres are postulated based on the experimental observations and previous reports.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Alternative material study for heat assisted magnetic recording transducer application

In heat assisted magnetic recording (HAMR), optical near field transducer (NFT) is a key component. Au is currently used as NFT material because of its strong surface plasmon effect. Due to the soft property of Au material, reliability of Au NFT becomes a key issue for realizing HAMR production. In this paper, the possibility of alternative materials, including transition metal nitrides (TMNs) and transparent conducting oxides (TCOs) to replace Au is studied. The results show that all of the listed TMN and TCO materials can meet the mechanical requirements at room temperature in terms of hardness and thermal expansion. An optical model, which includes optical waveguide, NFT and FePt media, is used to simulate NFT performances. The results indicate that the resonant wavelengths for NFT with TCO materials are longer than 1500 nm, which is not suitable for HAMR application. TMN materials are suitable for NFT application at wavelength band of around 800 nm. But the NFT efficiency is very low. ZrN is the best material among TMN materials and the efficiency of ZrN NFT is only 13% of the Au NFT's efficiency. Reducing refractive index (n) and increasing extinction coefficient (k) will both lead to efficiency increase. Increasing k contributes more in the efficiency increase, while reducing n has a relatively low NFT absorption. For materials with the same figure of merit, the NFT with larger k material has higher efficiency. Doping materials to increase the material conduction electron density and growing film with larger size grain may be the way to increase k and reduce n.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Electric field stimulation setup for photoemission electron microscopes

Manipulating magnetisation by the application of an electric field in magnetoelectric multiferroics represents a timely issue due to the potential applications in low power electronics and the novel physics involved. Thanks to its element sensitivity and high spatial resolution, X-ray photoemission electron microscopy is a uniquely suited technique for the investigation of magnetoelectric coupling in multiferroic materials. In this work, we present a setup that allows for the application of in situ electric and magnetic fields while the sample is analysed in the microscope. As an example of the performances of the setup, we present measurements on Ni/Pb(Mg{sub 0.66}Nb{sub 0.33})O{sub 3}-PbTiO{sub 3} and La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/PMN-PT artificial multiferroic nanostructures.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Magnetic structure of Sr 2 CuWO 6

Magnetic structure of the double perovskite Sr2CuWO6 was determined from neutron powder diffraction data. At 3 K the material is magnetically long-range ordered into a collinear antiferromagnetic structure described by a propagation vector k = (0, 1/2, 1/2) with the Cu-II moments of 0.57(1) mu(B) parallel to the a-axis. The result is in agreement with our previous prediction (Vasala et al 2014 Phys. Rev. B 89 134419) based on electronic structure calculations, showing that the three-dimensional magnetic long-range order is caused by relatively strong antiferromagnetic next-nearest-neighbor interactions.

double-perovskite oxide↗
DOE OSTI2024

Fe-carbide/Fe-oxide-based nanocomposites synthesized as magnetic nanomaterials via laser ablation synthesis in solution (LASiS)

Magnetic nanostructured materials (MNMs) have gained prominence in materials technology developments owing to their potential biomedical applications for hyperthermia cancer treatment, and transplant organ cryopreservation. Herein, we report the facile and cost-effective synthesis of Fe-based composite MNMs, comprising both Fe@Fe 2 O 3 and Fe 3 C@C core-shell nanoparticles (NPs), via Laser Ablation Synthesis in Solution (LASiS) using Fe targets ablated under acetone and toluene. Detailed materials characterizations using electron microscopy-based imaging, diffraction studies, and spectroscopic analyses - including Raman and Mössbauer spectroscopy - relate the structure-composition properties for different Fe-oxide/carbide phases in the aforesaid MNMs to their respective magnetic responses. Specifically, we confirm the presence of ultra-small (2–10 nm) amorphous Fe-oxide NPs, as well as Fe@Fe 2 O 3 core-shell NPs (20–40 nm) in the samples synthesized by ablating Fe under acetone. In contrast, samples synthesized under toluene indicate a higher concentration of Fe 3 C@C core-shell NPs (20–40 nm) with a relatively low concentration of Fe 2 O 3 NPs (2–10 nm). Furthermore, the crystallinity of the metallic phases and carbonaceous shell coatings are systematically increased by carrying out LASiS under heated toluene (up to ~95 °C). Importantly, mössbauer spectroscopy results indicate that the elevation in toluene temperature leads to an increase in the concentrations of Fe 3 C@C NPs from ~40 % to ~53 % (at.).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural and magnetic properties of the CeCo 5 –CeZn 5 solid solution and potential improvements upon iron substitution

In an effort to create high-performance permanent magnets with reduced critical rare earth content, we explored the CeCo 5-x T x (T = transition metal or metalloid) family of compounds to investigate the effect of substitution on the material’s magnetic properties. In our exploration of the CeCo 5-x Zn x system, we discovered a continuous solid solution at 900 °C between the CeCo 5 and CeZn 5 binary phases with ferromagnetism existing from the CeCo 5 compound to the intermediate CeCo 2.75 Zn 2.25 compound. Single crystal studies were also conducted revealing a relatively large anisotropy field of 11.5 T at 300 K for Ce 0.96 Ta 0.04 Co 4.35 Zn 0.65 . Here, the addition of iron Ce 0.79 Ta 0.07 Co 3.77 Fe 0.89 Zn 0.47 yielded further increases in Curie temperature and saturation magnetization to 800 K and 85.5 emu/g, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Giant Controllable Magnetization Changes Induced by Structural Phase Transitions in a Metamagnetic Artificial Multiferroic

We realize that a controllable metamagnetic transition from AFM to FM ordering would open the door to a plethora of new spintronics based devices that, rather than reorienting spins in a ferromagnet, harness direct control of a materials intrinsic magnetic ordering. In this study FeRh films with drastically reduced transition temperatures and a large magneto-thermal hysteresis were produced for magnetocaloric and spintronics applications. Remarkably, giant controllable magnetization changes (measured to be as high has ~25%) are realized and by manipulating the strain transfer from the external lattice when subjected to two structural phase transitions of BaTiO3 (001) single crystal substrate. These magnetization changes are the largest seen to date to be controllably induced in the FeRh system. Using polarized neutron reflectometry we reveal how just a slight in plane surface strain change at ~290C results in a massive magnetic transformation in the bottom half of the film clearly demonstrating a strong lattice-spin coupling in FeRh. By means of these substrate induced strain changes we show a way to reproducibly explore the effects of temperature and strain on the relative stabilities of the FM and AFM phases in multi-domain metamagnetic systems. In our study also demonstrates for the first time the depth dependent nature of a controllable magnetic order using strain in an artificial multiferroic heterostructure.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structure and Magnetic Properties of Lanthanide Nanocrystals

We have had considerable success on this project, particularly in the understanding of the relationship between nanostructure and magnetic properties in lanthanide nanocrystals. We also have successfully facilitated the doctoral degrees of Dr. Suseela Somarajan, in the Department of Physics and Astronomy, and Dr. Melissa Harrison, in the Materials Science Program. The following passages summarize the various accomplishments that were featured in 9 publications that were generated based on support from this grant. We thank the Department of Energy for their generous support of our research efforts in this area of materials science, magnetism, and electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Magnetic small-angle neutron scattering

Small-angle neutron scattering (SANS) is one of the most important techniques for microstructure determination, being utilized in a wide range of scientific disciplines, such as materials science, physics, chemistry, and biology. The reason for its great significance is that conventional SANS is probably the only method capable of probing structural inhomogeneities in the bulk of materials on a mesoscopic real-space length scale from roughly 1 to 300 nm. Moreover, the exploitation of the spin degree of freedom of the neutron provides SANS with a unique sensitivity to study magnetism and magnetic materials at the nanoscale. As such, magnetic SANS ideally complements more real-space and surface-sensitive magnetic imaging techniques, e.g., Lorentz transmission electron microscopy, electron holography, magnetic force microscopy, Kerr microscopy, or spin-polarized scanning tunneling microscopy. This review summarizes the recent applications of the SANS method to study magnetism and magnetic materials. Here, this includes a wide range of materials classes from nanomagnetic systems such as soft magnetic Fe-based nanocomposites, hard magnetic Nd-Fe-B-based permanent magnets, magnetic steels, ferrofluids, nanoparticles, and magnetic oxides to more fundamental open issues in contemporary condensed matter physics such as skyrmion crystals, noncollinear magnetic structures in noncentrosymmetric compounds, magnetic or electronic phase separation, and vortex lattices in type-II superconductors. Special attention is paid not only to the vast variety of magnetic materials and problems where SANS has provided direct insight, but also to the enormous progress made regarding the micromagnetic simulation of magnetic neutron scattering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗