Magnets, Magnets, Magnets!
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75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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Results for “Magnetics”
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The Nonpotentiality of Steady-state Coronal Magnetic Field Derived with Time-relaxation Magnetohydrodynamics Simulations Using Helioseismic and Magnetic Imager Three-component Magnetic Field Data
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Keiji Hayashi↗
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 ↗
Sensitivity of the magnetic axis to variations in the magnetic field
Lagrangian variational principles are used to locate the magnetic axis and to determine its sensitivity to variations in the magnetic field. Only the change in the magnetic field on axis is required to determine, to lowest order, the location of the new magnetic axis. Using a simple example, namely, the magnetic field produced by a set of current-carrying filaments (a.k.a. coils), the variation in the coil geometry that induces the largest change in the magnetic axis is determined using singular value decomposition.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Electron-Only Magnetic Reconnection and Inverse Magnetic-Energy Transfer at Subion Scales
We derive, and validate numerically, an analytical model for electron-only magnetic reconnection applicable to strongly magnetized plasmas. Our model predicts subion-scale reconnection rates significantly higher than those pertaining to large-scale reconnection, aligning with recent observations and simulations. Here, we apply this reconnection model to the problem of inverse magnetic energy transfer at subion scales. We derive time-dependent scaling laws for the magnetic energy decay and the typical magnetic structure dimensions that differ from those previously found in the magnetohydrodynamics regime. These scaling laws are validated via two- and three-dimensional simulations, demonstrating that subion-scale magnetic fields can reach large, system-size scales via successive coalescence.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Magnetic Field Mapping Design for the MOLLER Spectrometer Magnets at Jefferson Lab
The Thomas Jefferson National Accelerator Facility (JLab) has developed a unique spectrometer system to study the weak interaction between electrons. The "Measurement of Lepton-Lepton Electroweak Reaction" (MOLLER) experiment, utilizing JLab's recent 12 GeV electron beam upgrade, is scheduled to operate for three years. Central to the MOLLER experiment are five water-cooled toroidal magnets, each with a unique geometry and seven-fold symmetry, designed to focus the particles. These magnets generate the magnetic field needed to separate incident beam electrons scattered from target electrons (Møller scattering) and protons (elastic e-p scattering) within a liquid hydrogen target. Here, this paper details the magnet field measuring technique developed to map all five MOLLER toroidal magnets at multiple locations inside and along the bore. It covers the design, mounting, and operation of the probe, along with the calibration procedure to determine the field and to prepare a field map for GEANT4 analysis. Additionally, the paper addresses the challenges of accurately measuring low magnetic fields.
Ghoshal, Probir K. [Thomas Jefferson National Acce↗
Status of permanent magnet radiation resiliency studies at CEBAF
An ongoing investigation for the future of Jefferson Lab’s Continuous Electron Beam Accelerator Facility (CEBAF) lies in upgrading its maximum nominal energy using Fixed-Field Alternating-gradient (FFA) technology for its recirculating arcs, using permanent magnets for the FFA arcs. A common concern among the community is the degradation of these permanent magnets during operation due to the radiation environment in which they will be present. This work, funded by a Laboratory Directed R&D grant, aims to measure the permanent magnet degradation in the CEBAF tunnel enclosure, and extrapolate to the energies expected from the upgrade. We present the latest results of this study, as well as plans moving forward.
Accelerator Physics↗
Large-scale Linear Magnetic Holes with Magnetic Mirror Properties in Hybrid Simulations of Solar Wind Turbulence
Magnetic holes (MHs) are coherent magnetic field dips whose size ranges from fluid to kinetic scale, ubiquitously observed in the heliosphere and in planetary environments. Despite the long-standing effort in interpreting the abundance of observations, the origin and properties of MHs are still debated. In this Letter, we investigate the interplay between plasma turbulence and MHs, using a 2D hybrid simulation initialized with solar wind parameters. We show that fully developed turbulence exhibits localized elongated magnetic depressions, whose properties are consistent with linear MHs frequently encountered in space. The observed MHs develop self-consistently from the initial magnetic field perturbations by trapping hot ions with large pitch angles. Ion trapping produces an enhanced perpendicular temperature anisotropy that makes MHs stable for hundreds of ion gyroperiods, despite the surrounding turbulence. We introduce a new quantity, based on local magnetic field and ion temperature values, to measure the efficiency of ion trapping, with potential applications to the detection of MHs in satellite measurements. We complement this method by analyzing the ion velocity distribution functions inside MHs. Our diagnostics reveal the presence of trapped gyrotropic ion populations, whose velocity distribution is consistent with a loss cone, as expected for the motion of particles inside a magnetic mirror. Our results have potential implications for the theoretical and numerical modeling of MHs.
79 ASTRONOMY AND ASTROPHYSICS↗
Constraints of magnetic field which magnetized the Farmington meteorite parant body
Analysis indicates the following: (1) the parent body of the Farmington meteorite experienced sufficient heating (probably from shock accompanying a major collision occurring 520 million years ago) to erase the record of any magnetization acquired prior to that event; therefore, (2)the observed magnetization in the Farmington meteorite must have been acquired after the collision; and (3)shockproduced magnetization is unlikely, because of the finite cooling time indicated by the burial depth of approximately several meters. The possibility of shock or irradiation-produced magnetizations is proposed as an experimental study, even though neither appears likely to have produced the magnetic field which produced the magnetization in the parent body of the Farmington meteorite.
Rowe, M. W.↗
Constraints on magnetic field which magnetized the Farmington meteorite parent body
The parent body of the Farmington meteorite experienced sufficient heating, probably from shock accompanying a major collision occurring 520 million years ago, to erase the record of any magnetization acquired prior to that event. Therefore, the observed magnetization in the Farmington meteorite must have been acquired after the collision. Shock-produced magnetization is unlikely because of the finite cooling time indicated by the burial depth of over several meters. The possibility of shock or irradiation-produced magnetizations should be studied experimentally, even though neither appears likely to have produced the magnetic field which produced the magnetization in the parent body of the Farmington meteorite.
Rowe, M. W.↗
Stellar magnetic fields. 1: The role of a magnetic field in the peculiar M giant, HD 4174
Coronal heating by resonant absorption of Alfvenic surface waves (quiescent), and magnetic tearing instabilities (impulsive), is discussed with emphasis on three principles which may have application to late-type evolved stars. (1) If sq B/8 pi greater than sq. rho V is observed 2 in a stellar atmosphere, then the observed magnetic field must originate in an interior dynamo. (2) Low mass loss rates could imply the presence of closed magnetic flux loops within the outer atmosphere which constrain hydrodynamic flows when the magnetic body forces exceed the driving forces. (3) given that such magnetic loops effect an enhancement of the local heating rate, a positive correlation is predicted between the existence of a corona and low mass loss rates. These principles are applied to the M giant star HD 4174, which is purported to have a kilogauss magnetic field. Several of its spectroscopic peculiarities are shown to be consistent with the above principles, and further observational checks are suggested.
Stencel, R. E.↗
Stellar magnetic fields - The role of a magnetic field in the peculiar M giant, HD 4174
Principles of coronal heating via basic electrodynamic effects, viz., resonant absorption of Alfven surface waves (quiescent) and magnetic tearing instabilities (impulsive), are detailed to argue three principles which may have application to late-type evolved stars. First, if one observes that B-squared/8 pi is much greater than rho times v-squared in a stellar atmosphere, then the observed magnetic field must originate in an interior dynamo. Second, low mass-loss rates could imply the presence of closed magnetic flux loops within the outer atmosphere, which constrain hydrodynamic flows when the magnetic body forces exceed the driving forces. Third, given that such magnetic loops effect an enhancement of the local heating rate, a positive correlation is predicted between the existence of a corona and low mass-loss rates. Application of these principles is made in the case of the peculiar M giant star HD 4174, which is purported to have a kilogauss magnetic field. Several of its spectroscopic peculiarities are shown to be consistent with the above principles, and further observational checks are suggested. Possible application to dMe and RS CVn objects is sketched.
Stencel, R. E.↗
Magnetic buoyancy and the escape of magnetic fields from stars
A loss of magnetic flux through the free surface of a star into the surrounding space has important implications for the generation of the field within the star. The present investigation is concerned with the physics of the escape of net azimuthal flux from a star. The obtained results are used as a basis for the interpretation of some recent observations of the detailed behavior of magnetic fields emerging through the surface of the sun. The buoyancy of an isolated horizontal magnetic flux tube beneath the surface of a star causes the tube to rise at a rate comparable to the Alfven speed. The necessary conditions for escape of the flux are considered along with aspects of magnetic buoyancy, and the conditions on the sun. It appears that the observed retraction of bipolar magnetic fields at the end of their life at the surface is the one phenomenon which requires dynamical intervention. Attention is given to known dynamical effects which suppress the buoyant rise of an azimuthal magnetic field.
Parker, E. N.↗
Effects of wear on structure-sensitive magnetic properties of ceramic ferrite in contact with magnetic tape
Wear experiments and electron microscopy and diffraction studies were conducted to examine the wear and deformed layers in single-crystal Mn-Zn (ceramic) ferrite magnetic head material in contact with magnetic tape and the effects of that contact on magnetic properties. The crystalline state of the single-crystal magnetic head was changed drastically during the sliding process. A nearly amorphous structure was produced on its wear surface. Deformation in the surficial layer of the magnetic head was a critical factor in readback signal loss above 2.5 dB. The signal output level was reduced as applied normal load was increased. Considerable plastic flow occurred on the magnetic tape surface with sliding, and the signal loss due to the tape wear was approximately 1 dB.
Miyoshi, K.↗
Magnetization of lower crust and interpretation of regional magnetic anomalies - Example from Lofoten and Vesteralen, Norway
During the last 20 years, studies have been conducted regarding the regional, or long-wavelength, geomagnetic anomalies of the lower crust of the earth. The present paper is mainly concerned with the petrologic and geophysical interpretation of the observed features. Attention is given to magnetic mineralogy and magnetic properties of high-grade rocks from Lofoten and Vesteralen, regional geology and geophysics, field measurements and sampling, magnetic mineralogy of the lower crust, the effects of metamorphism upon magnetic mineralogy and magnetic properties of high-grade rocks, susceptibility-temperature relations and the Hopkinson effect, and petrologic sources of regional crustal magnetic anomalies.
Schlinger, C. M.↗
Magnetic field and remanent magnetization effects of basin-forming impacts on the moon
Maps of the distribution of lunar surface magnetic fields produced by the electron reflection method have shown that the largest observed concentrations of lunar crustal magnetization occur antipodal (diametrically opposite) to four relatively young large impact basins: Imbrium, Orientale, Serenitatis, and Crisium. A model is proposed here for the formation of these magnetization concentrations (or 'magcons') in which the partially ionized vapor cloud produced in a hypervelocity (greater than 10 km/s) basin-forming impact expands around the moon forcing a preexisting ambient magnetic field to be concentrated for a brief (less than 1 day) time period in the antipodal zone. Acquisition of magnetic remanence during the period of compressed field amplification may occur by one of several mechanisms, such as shock remanence by impact of solid secondaries ejected from the basin-forming event. The model implies that basin-forming impacts have played a major role in determining the large-scale distribution of crustal magnetization detectable from lunar orbit.
Hood, L. L.↗
Magnetic flux transport of decaying active regions and enhanced magnetic network
Several series of coordinated observations on decaying active regions and enhanced magnetic network regions on the sun were carried out jointly at Big Bear Solar Observatory and at the Huairou Solar Observing Station of the Bejing Astronomical Observatory in China. The magnetic field evolution in several regions was followed closely for three to seven days. The magnetic flux transport from the remnants of decayed active regions was studied, along with the evolution and lifetime of the magnetic network which defines the boundaries of supergranules. The magnetic flux transport in an enhanced network region was studied in detail and found to be negative. Also briefly described are some properties of moving magnetic features around a sunspot. Results of all of the above studies are presented.
Wang, Haimin↗
Remanent magnetism of HED meteorites: Implications for their evolution and ancient magnetic fields
The magnetic properties of extraterrestrial materials, in particular natural remanent magnetization (NRM), is a potentially useful study for detecting ancient Solar System magnetic fields and for elucidating meteorite evolutionary processes. Results are presented for the following: howardites--Kapoeta, Petersburg, Le Teilleul, and EET 87503; eucrites--Sioux County and Millbillillie; and diogenites--Shalka and Johnstown. Significant features of their magnetism are within-sample in homogeneity of NRM directions in several of the meteorites and within-sample uniformity of axes of an isotropy of magnetic susceptibility. Both these phenomena bear on the meteorites' evolution and the timing of the magnetization process.
Collinson, D. W.↗