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At least 559 records · Page 31

Fiber-optic diagnostic system for future accelerator magnets

The next generation high energy physics accelerators will require magnetic fields at ~20 T. HTS coils will be an essential component of future accelerator magnets and several efforts are currently dedicated on designing 20 T HTS- LTS hybrid magnets. Among the existing challenges, there is the lack of a robust quench detection system for hybrid magnet technology. Another big challenge is represented by the high number of training quenches required by Nb3Sn magnets to reach performance level. In this framework it is important to find a tool that allow local real-time monitoring of magnet strain and temperature. In this paper, we propose the use of fiber optics sensors for diagnostic and quench detection in future accelerator superconducting magnets. Discrete and distributed fiber optic sensors have demonstrated to be a promising tool. The goal is to instrument hundreds of accelerator superconducting magnets and to move beyond the proof-of-concept level. Significant developments are still needed. Here, we are going to present the most recent results and discuss the most urgent technical developments in order to make those sensors a robust and reliable diagnostic tool for accelerator superconducting magnets over the next 10 year. We foresee that discrete fiber sensors will be a stable diagnostic probe for superconducting magnets over the next 3 to 5 years. More R&D work will be necessary for distributed fibers. The most urgent needs are the increase of sample rate and sensitivity. Close collaboration with vendors will be necessary to improve mechanical properties and fabrication processes in order to produce hundreds of meters of fiber and instrument a large number of accelerator superconducting magnets. Those R&D efforts will last up to 10 years with a founding level that spans between 5-10 M$.

43 PARTICLE ACCELERATORS↗

MAGNETICALLY SUSPENDED CANNED ROTOR PUMPS FOR THE INTEGRAL MOLTEN SALT REACTOR

This project developed a molten salt pump design for small modular reactors, concentrated solar, and Gen IV nuclear reactors with a magnetically levitated rotor that can operate at temperatures of up to 700 °C. This eliminates the need for rotating seals and roller element bearings which require maintenance and are prone to failure. The pump design is also more compact than existing molten salt pump designs which require long shafts to thermally isolate the electric motor. The aims of the project are to: 1) design and test the molten salt pump, 2) develop and test a high temperature position sensor needed for magnetic bearing control, and 3) develop and test high temperature coil fabrication methods for electric motor and magnetic bearing fabrication. To develop the high temperature coils, conductor materials were analyzed for oxidation, diffusion, cladding, and resistivity. Of the candidate conductor materials that met the requirements, silver was chosen. The long-term impact of radiation on silver resistivity was analyzed by developing a model of a generic molten salt fast reactor to model the conductor irradiation in worst case scenarios. The analysis showed that increased resistivity due to transmutation of silver decreases exponentially with the reactor reflector thickness. Different electrical insulation materials were tested and the final high temperature coils developed were able to withstand conductor to ground voltages up to 1800 V before insulation breakdown. Magnetic bearings require high-precision high-speed measurements of the rotor position to operate. Current commercial position sensors can only operate up to 550 °C so a novel position sensor was developed that can operate up to 800 °C. These sensors were also designed to measure the position of the metallic rotor through a thin metallic corrosion barrier that protects that coils, insulation, and magnetic cores so that the salt containment barrier does not have any penetrations. The high-temperature sensor was tested and had comparable performance to commercially available inductive position sensors. The sensor design and signal processing has led to several invention disclosures. The magnetically levitated molten salt pump design was completed and analyzed. The chloride salt test loop at Oak Ridge National Laboratory was chosen to test the pump and the pump hydraulics and power were designed for the test loop flow and pressure requirements. Classes of motor designs that do not utilize permanent magnetic were considered for the high-temperature motor. After extensive analysis of their performance, a synchronous reluctance motor was chosen for the pump. The design was refined and analyzed to optimize performance. The magnetic bearings were designed to meet the force and frequency requirements necessary to levitate the rotor and reject disturbances from rotor imbalance, motor forces, and hydraulic forces. Compliant mounts for the position sensors were designed that would not damage the ceramic sensor components and maintain sensor alignment over a wide temperature range. A thermal hydraulic analysis of the molten salt coolant flow used to cool the rotor and stator was performed to ensure that the maximum temperature in the rotor and stator will not exceed 725 °C. The corrosion barrier and casing were designed to maintain the salt fluid boundary by using compliant features to absorb large expansion mismatches due to different coefficients of thermal expansion (CTE). Finally, the salt drain and fill systems were designed along with the pump support structure, integration with the test loop, and thermal insulation and heating. Corrosion barrier fabrication experiments were performed to assess using laser cladding to apply a sub-millimeter corrosion barrier to the surface of a Fe-Co-V magnetic core material. The cladding method showed minimal mixing between materials at their interface and withstood temperature cycling without damage to the cladding. The technology commercialization is focused on the high-temperature position sensors and there has been significant interest from the nuclear industry in utilizing these sensors along with some interest from the aerospace industry. The project also led to a research collaboration with a fusion energy industrial partner to study barriers to scaling the pump design from the kW size to the MW size. This research collaboration will also study methods to create high-temperature coils that have conductor to ground breakdown voltages above 5 kV. The successful development of high-temperature electromagnetic coils and high-temperature position sensors greatly increases the temperature limits for electromagnetic devices that don’t rely on permanent magnets. This includes electric motors, magnetic bearings, linear actuators, rotary position and velocity sensing, actuated valves, and generators to name a few. This will fill a current need in molten salt reactors, concentrated solar, and fusion energy for these critical peripheral devices needed for practical reactor designs that do not currently have commercial solutions.

Hines, J Wesley↗

Indirect additive manufacturing process for fabricating bonded soft magnets

A bonded soft magnet object comprising bonded soft magnetic particles of an iron-containing alloy having a soft magnet characteristic, wherein the bonded soft magnetic particles have a particle size of at least 200 nm and up to 100 microns. Also described herein is a method for producing the bonded soft magnet by indirect additive manufacturing (IAM), such as by: (i) producing a soft magnet preform by bonding soft magnetic particles with an organic binder, wherein the magnetic particles have an iron-containing alloy composition with a soft magnet characteristic, and wherein the particles of the soft magnet material have a particle size of at least 200 nm and up to 100 microns; (ii) subjecting the preform to an elevated temperature sufficient to remove the organic binder to produce a binder-free preform; and (iii) sintering the binder-free preform at a further elevated temperature to produce the bonded soft magnet.

Paranthaman, Mariappan Parans↗

MnBi-based magnets prepared from melt-spun alloys: Effect of $α → β$ phase transformation during field annealing

The temperature of the annealing treatment applied to the MnBi alloys with the intention to stabilize the α -MnBi “low-temperature” phase – a promising material for the rare-earth-free permanent magnets – is usually kept below the range of the β -Mn 1.08 Bi “high-temperature” phase. This work is focused on the investigation of the effects of partial and complete α → β phase transformation in bulk magnetic-field-annealed magnets on their structure and magnetic properties. MnBi alloys modified with In, Mg and Sb were melt-spun, compacted to their full density and then heated in a magnetic field of 30 kOe to temperatures sufficiently high for the beginning of the α → β transformation. A heating of 15 °C/min was used which was immediately followed by cooling at the rate of 7.5 °C/min; the degree of the phase transformation was measured by in situ monitoring of changes in the sample magnetization. In all the studied alloys, the α → β transformation was found to improve the [0 0 1] fiber texture induced by the applied magnetic field, although it simultaneously decreased the coercivity. A partial transformation has resulted in a 11% increase of the maximum energy product for the Mn 50 Bi 49 Sb 0.5 In 0.5 magnet, to 8.3 MGOe, and a 3% increase for the Mn 50 Bi 46 Mg 3 Sb 0.5 In 0.5 magnet, to 12.8 MGOe. In the latter alloy, the α → β and reverse transformations were found to initially occur in well-defined pockets leading to clusters of large, highly textured α crystallites. In the Mn 50 Bi 48.5 Sb 1.5 magnet, only part of the α phase could be recovered after the transformation, which instead promoted the paramagnetic MnBi 0.9 Sb 0.1 phase.

36 MATERIALS SCIENCE↗

Intertwined Topological and Magnetic Orders in Atomically Thin Chern Insulator MnBi 2 Te 4

The interplay between band topology and magnetic order plays a key role in quantum states of matter. MnBi 2 Te 4 , a van der Waals magnet, has recently emerged as an exciting platform for exploring Chern insulator physics. Its layered antiferromagnetic order was predicted to enable even-odd layer-number dependent topological states, supported by promising edge transport measurements. Furthermore, it becomes a Chern insulator when all spins are aligned by an applied magnetic field. However, the evolution of the bulk electronic structure as the magnetic state is continuously tuned and its dependence on layer number remains unexplored. Here, employing multimodal probes, we establish oneto-one correspondence between bulk electronic structure, magnetic state, topological order, and layer thickness in atomically thin MnBi 2 Te 4 devices. As the magnetic state is tuned through the canted magnetic phase, we observe a band crossing, i.e., the closing and reopening of the bulk bandgap, corresponding to the concurrent topological phase transition. Surprisingly, we find that the even- and odd-layer number devices exhibit a similar topological phase transition coupled to magnetic states, distinct from recent theoretical and experimental reports. Our findings shed new light on the interplay between band topology and magnetic order in this newly discovered topological magnet and validate the band crossing with concurrent measurements of topological invariant in a continuously tuned topological phase transition.

36 MATERIALS SCIENCE↗

Switching interlayer magnetic order in bilayer CrI 3 by stacking reversal

CrI 3 , a hot two-dimensional (2D) magnet, exhibits complex magnetism depending on the number of layers and interlayer stacking patterns. For bilayer CrI 3 , the interlayer magnetism can be tuned between ferromagnetic (FM) and antiferromagnetic (AFM) order by manipulating the stacking order. However, the stacking is mostly modified through translation between the layers, while the effect of rotation between the layers on the interlayer magnetic order has not yet been fully investigated. Here, we considered three energetically stable stacking patterns R$\bar3$ with combining macron], C2/m and AA in bilayer CrI 3 , and their reversed counterparts R$\bar3$ with combining macron]-r, C2/m-r and AA-r through rotating one layer by 180° with respect to the other layer. Our first-principles calculations suggest that the interlayer magnetic ground state can be switched from AFM to FM (or FM to AFM) by reversing the stacking pattern. A detailed microscopic analysis was carried out by magnetic force theory calculations on C2/m stacking which favors AFM and C2/m-r stacking which favors FM. The interlayer magnetic interactions and the origin of the magnetic order change were revealed through specific orbital analysis. Our work demonstrates that stacking rotation can also tune the interlayer magnetism of CrI 3 and provides insight into its interlayer magnetic properties at the microscopic level.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Iodine orbital moment and chromium anisotropy contributions to CrI 3 magnetism

The recent discovery of two-dimensional (2D) magnets, with a number of interesting magnetic properties, has drawn much interest due to their potential for future 2D spintronic device applications. CrI 3 , a van der Waals magnet, exhibits two-dimensional ferromagnetism even in monolayer form, stabilized by strong magnetic anisotropy. Its interlayer magnetic ordering is coupled to structural layer stacking, implying that the charge density distribution mediating van der Waals interactions plays a key role in the magnetic interaction between the layers. Using polarization-dependent x-ray spectroscopy, we investigated the response of the electronic environment around Cr and I sites to structural changes of layer stacking order. The highly anisotropic nature of the Cr local environment is significantly enhanced and is accompanied by changes in the valence band, in the rhombohedral phase. Magnetic spectroscopy measurements reveal a sizable iodine orbital moment, indicating the iodine contribution to magnetic anisotropy. Finally, our results uncover an important role for the extended nature of anisotropic Cr orbital states in dictating interlayer magnetic interactions and the iodine contribution to magnetic anisotropy.

36 MATERIALS SCIENCE↗

Calculation of permanent magnet arrangements for stellarators: a linear least-squares method

A problem arising in several engineering areas is to design magnets outside a volume that produce a desired magnetic field inside it. One instance of this problem is stellarator design, where it has recently been shown that permanent magnets can provide the required shaping of the magnetic field. Here we demonstrate a robust and efficient algorithm REGCOIL_PM to calculate the spatial distribution of these permanent magnets. The procedure involves a small number of fixed-point iterations, with a linear least-squares problem solved at each step. Furthermore, the method exploits the Biot–Savart Law's exact linearity in magnetization density and approximate linearity in magnet size, for magnets far from the target region. No constraint is placed on the direction of magnetization, so Halbach solutions are found naturally, and the magnitude of the magnetization can be made uniformly equal to a target value.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Semihard Iron-Based Permanent-Magnet Materials

Permanent magnets generally require a favorable, but difficult-to-achieve combination of high magnetization, Curie point, and magnetic anisotropy. Thus there have been few, if any, viable permanent magnets developed since the 1982 discovery of Nd 2 Fe 14 B. In this work we point out, both by direct first-principles calculations on the iron carbides and silicides Fe 5 C 2 , Fe 5 SiC, and Fe 7 C 3 as well as a discussion of recent experimental findings, that there are numerous rare-earth-free iron-rich potential permanent-magnet materials with sufficient intrinsic magnetic properties to reasonably achieve room-temperature energy products of 20–25 MG Oe. This is substantially better than the performance of the best available rare-earth-free magnets based on ferrite, as well as shape-anisotropy-employing alnico. These magnets could plausibly fill, at low cost, the present performance “gap” between the best rare-earth-free magnets and rare-earth magnets such as Nd 2 Fe 14 B and Sm-Co.

36 MATERIALS SCIENCE↗

Unconventional magnetic order emerging from competing energy scales in the new R Rh 3 Si 7 intermetallics ( R = Gd-Yb)

The competition between Ruderman-Kittel-Kasuya-Yosida (RKKY), crystal electric field (CEF), and Kondo energy scales has recently emerged at the heart of complex magnetism in several Ce- or Yb-based intermetallics. Hard axis magnetic order has been observed in a handful of these compounds, independent of the crystal symmetry, size of the ordered moment, or the relative scale of the Kondo and magnetic ordering temperatures. This raises the question of the role of each energy scale in driving the ground state properties. In focusing on a single class of compounds, the rhombohedral RRh 3 Si 7 , we compare the anisotropy and magnetic ground states in members of this series with only RKKY interactions (R = Gd), or RKKY and CEF effects (R = Tb-Tm), with the behavior of the R = Yb compound, where all three energy scales (RKKY, CEF, Kondo) are at play. Moreover, we extend the comparison to two other isostructural Kondo systems YbIr 3 Si 7 and YbIr 3 Ge 7 , where hard axis magnetic order is also observed. The non-Kondo compounds RRh 3 Si 7 (R = Tb-Tm) lack the complexity of magnetic order along the hard CEF axis, pointing to the dominant role of the Kondo effect in driving this magnetic order. Furthermore, the CEF-RKKY competition is still responsible for complex magnetic ground states, and it appears that the electronic and magnetic degrees of freedom are entangled in all magnetic members of this series of compounds.

36 MATERIALS SCIENCE↗

Additive Manufacturing of Isotropic NdFeB PPS Bonded Permanent Magnets

Extrusion based additive manufacturing of polymer composite magnets can increase the solid loading volume fraction with greater mechanical force through the printing nozzle as compared to traditional injection molding process. About 63 vol% of isotropic NdFeB magnet powders were compounded with 37 vol% of polyphenylene sulfide and bonded permanent magnets were fabricated while using Big Area Additive Manufacturing without any degradation in magnetic properties. The polyphenylene sulfide bonded magnets have a tensile stress of 20 MPa, almost double than that of nylon bonded permanent magnets. Additively manufactured and surface-protective-resin coated bonded magnets meet the industrial stability criterion of up to 175 °C with a flux-loss of 2.35% over 1000 h. They also exhibit better corrosion resistance behavior when exposed to acidic (pH = 1.35) solution for 24 h and also annealed at 80 °C over 100 h (at 95% relative humidity) over without coated magnets. Thus, polyphenylene sulfide bonded, additively manufactured, protective resin coated bonded permanent magnets provide better thermal, mechanical, and magnetic properties.

36 MATERIALS SCIENCE↗

Ironsand (Titanomagnetite-Titanohematite): Chemistry, Magnetic Properties and Direct Applications for Wireless Power Transfer

Ironsand is an abundant and inexpensive magnetic mineral resource. However, the magnetic properties of unprocessed ironsand are often inadequate for any practical applications. In this work, the applicability of ironsand for use as a component in a soft magnetic composite for large-scale inductive power transfer applications was investigated. After magnetic separation, the chemical, structural and magnetic properties of ironsand sourced from different locations were compared. Differences observed in the DC magnetic properties were consistent with changes in the chemical compositions obtained from X-ray Absorption Near-Edge Spectroscopy (XANES), which suggests varying the titanohematite to titanomagnetite content. Increased content in titanomagnetite and magnetic permeability correlated well with the total Fe content in the materials. The best-performing ironsand with the highest permeability and lowest core losses was used alongside Mn,Zn-Ferrite particles (ranging from ~100 μm to 2 mm) to fabricate toroid cores with varying magnetic material loading. It was shown that ironsand can be used to replace up to 15 wt.% of the magnetic materials with minimal impact on the composite magnetic performance, thus reducing the cost. Ironsand was also used as a supporting material in a single-rail wireless power transfer system, effectively increasing the power transfer, demonstrating potential applications to reduce flux leakage.

36 MATERIALS SCIENCE↗

Design of B1pF-A Large Aperture Dipole Magnet for EIC

The design of interaction region (IR) magnets for the Electron Ion Collider (EIC), demands tight boundary conditions on the magnet design given by the high field requirements and the proximity of electron and hadron beams within a common yoke and resultant crosstalk. Here, this article discusses the electromagnetic design of the superconducting collared magnet B1pF. The magnet will be built as the prototype for several collared magnets (dipoles and quadrupoles) for the hadron beam in the forward direction of the IR. The magnet design is based on a single layer coil with an inner diameter of 300 mm over a slot length of 3 m. The magnet produces an integral field of 10.34 T.m at a current of 11.9 kA to produce a nominal field of about 3.96 T at its center. Given by the common Rutherford cable parameters, the magnet will be used as a baseline for optimization of all the collared magnets. The article further discusses yoke optimizations, quench analysis, coil end design and efforts on fine tuning of field quality.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Nonvolatile Magnetoelectric Switching of Magnetic Tunnel Junctions with Dipole Interaction

The magnetoelectric effect is technologically appealing because of its ability to manipulate magnetism using an electric field rather than magnetic field or current, thus providing a promising solution for the development of energy-efficient spintronics. Although 180° magnetization switching is vital to spintronic devices, the achievement of 180° magnetization switching via magnetoelectric coupling is still a fundamental challenge. Here, in this work, voltage-driven full resistance switching of a magnetic tunnel junction (MTJ) with dipole interaction on a ferroelectric substrate through switchable parallel/antiparallel magnetization alignment is demonstrated. Parallel magnetization alignment along the y direction is obtained under a bias magnetic field. By rotating the magnetic easy axis via strain-mediated magnetoelectric coupling, the parallel magnetizations in the MTJ reorient to the x axis with opposite paths because of dipole interaction, thus resulting in antiparallel alignment. Moreover, this voltage switching of MTJs is nonvolatile owing to variations in dipole interaction and can be well understood via phase field simulations. The results provide an avenue to realize electrical switching of MTJs and are significant for exploring energy-efficient spintronic devices.

36 MATERIALS SCIENCE↗

3D Quantum Anomalous Hall Effect in Magnetic Topological Insulator Trilayers of Hundred‐Nanometer Thickness

Magnetic topological states refer to a class of exotic phases in magnetic materials with the non-trivial topological property determined by magnetic spin configurations. An example of such states is the quantum anomalous Hall (QAH) state, which is a zero magnetic field manifestation of the quantum Hall effect. Current research in this direction focuses on QAH insulators with a thickness of less than 10 nm. Here, molecular beam epitaxy (MBE) is employed to synthesize magnetic TI trilayers with a thickness of up to ≈106 nm. It is found that these samples exhibit well-quantized Hall resistance and vanishing longitudinal resistance at zero magnetic field. By varying the magnetic dopants, gate voltages, temperature, and external magnetic fields, the properties of these thick QAH insulators are examined and the robustness of the 3D QAH effect is demonstrated. The realization of the well-quantized 3D QAH effect indicates that the nonchiral side surface states of the thick magnetic TI trilayers are gapped and thus do not affect the QAH quantization. The 3D QAH insulators of hundred-nanometer thickness provide a promising platform for the exploration of fundamental physics, including axion physics and image magnetic monopole, and the advancement of electronic and spintronic devices to circumvent Moore's law.

36 MATERIALS SCIENCE↗

63,65 Cu NMR study of the magnetically ordered state of the multiferroic CuFeO 2

In this work, field-swept 63,65 Cu NMR spectra under magnetic fields up to 8.3 T at a constant NMR frequency and temperatures T < 12 K on a single crystalline sample of multiferroic CuFeO 2 were measured and analyzed. When the magnetic field is applied along the c axis, a nearly zero internal magnetic field at the Cu site in magnetic ordered state was observed. This is explained by the perfect cancellation of the internal fields produced by the 6 nearest neighbor Fe 3+ ( S = 5/2) ions, revealing the magnetic structure to be a collinear four-sublattice structure. On the other hand, when the magnetic field is applied along the ab plane, we observed a finite internal field at the Cu sites, which is due to the canting of the Fe moments. Strong change in the NMR signal intensity is observed around 7–8 T, corresponding to the magnetic phase transition from the collinear magnetic to ferroelectric incommensurate states. The ratio of the two magnetic phases significantly depends on the history of the change in the external magnetic field and the temperature of the sample. The details of history dependence of the ratio were discussed.

36 MATERIALS SCIENCE↗

Internal defect detection and characterization of samarium-cobalt sintered magnets by ultrasonic testing technique

Excessive quantities of samarium-cobalt (Sm-Co) magnet material are being scrapped needlessly due to a lack of understanding of inhomogeneity distribution and unacceptable internal defects. If there is a way to identify, locate, characterize and when needed separate the defective portions of magnet material, utilization can be increased and product quality improved. Further, the magnets’ magnetic and mechanical performance can be improved by reducing the occurrence of internal defects. This paper reports on a cost-effective and efficient nondestructive evaluation method based on an ultrasonic testing (UT) technique applied for detecting and characterizing internal defects in Sm-Co sintered magnets. Applying the UT technique will allow users to comprehensively analyze internal defects, such as inclusions, porosity, microcracks, and other structural irregularities, check for homogeneity and anomalous regions and give the locations of these internal anomalies and defects within the Sm-Co sintered magnets. The UT technique can also be applied to other rare-earth permanent magnets, such as sintered or die-upset neodymium-iron-boron (Nd-Fe-B) magnets. The UT technique can effectively guide quality control and acceptable product selection, in addition to optimizing the magnet alloy design and production processes. Therefore, it can facilitate the improvement of magnet manufacturing efficiency and machinability, reduce scrap, prolong service life, increase the use of what would be post-production waste, and enhance product reuse and recycling at end-of-life disposition.

36 MATERIALS SCIENCE↗

Geometric control of magnetic domain morphology in electrodeposited Ni rich NiPt mesoscopic wires

In this paper, we study the electrodeposited Ni—Pt magnetic wires, exploring the mechanisms by which changes in geometry and composition influence the local magnetic structure. The samples were prepared by electrodeposition, their elemental composition was analyzed by energy dispersive X-ray spectroscopy, and phase analysis was carried out by an X-ray diffraction measurement. Magnetic force microscopy measurements, and magnetic force microscopy measurements in magnetic field were carried out to study the domain morphology of the prepared samples. Magnetization characteristics were measured via vibrating sample magnetometry mode of a superconducting quantum interference device. Here, the results were analyzed and compared with micromagnetic simulations. It is shown that a strong perpendicular magnetic anisotropy is responsible for the characteristic checkerboard-like surface magnetization patterns, which can be tuned by geometrical constriction and Ni content. Understanding these relationships provides insights into the design of magnetic materials with tailored properties for advanced applications, like magnetic sensors.

Binary alloy↗