Scale Magnetic Field Research Articles

Detection of magnetospheric ion drift patterns at Mars

Mars lacks a global magnetic field, and instead possesses small-scale crustal magnetic fields, making its magnetic environment fundamentally different from intrinsic magnetospheres like those of Earth or Saturn. Here we report the discovery of magnetospheric ion drift patterns, typical of intrinsic magnetospheres, at Mars using measurements from Mars Atmosphere and Volatile EvolutioN mission. Specifically, we observe wedge-like dispersion structures of hydrogen ions exhibiting butterfly-shaped distributions (pitch angle peaks at 22.5°−45° and 135°−157.5°) within the Martian crustal fields, a feature previously observed only in planetary-scale intrinsic magnetospheres. These dispersed structures are the results of drift motions that fundamentally resemble those observed in intrinsic magnetospheres. Our findings indicate that the Martian magnetosphere embodies an intermediate case where both the unmagnetized and magnetized ion behaviors could be observed because of the wide range of strengths and spatial scales of the crustal magnetic fields around Mars.

Optimization of composite Helmholtz coils towards high magnetic uniformity

Helmholtz coils are widely used in biomedicine, aerospace, and other fields due to their simple structure and remarkable magnetic properties. However, the uniform areas they generate are not suitable for conducting scientific experiments with large equipment. In order to improve the uniformity and scale of the uniform magnetic field, a novel scheme is proposed in this paper. Two auxiliary coils are added on both sides of the Helmholtz coils to optimize the magnetic field. The non-dominated Sorting Genetic Algorithm (NSGA-II) was used to optimize the structural parameters of the improved model, while orthogonal experiments were conducted to obtain initial values for better adaptability of influencing factors. A comparison was made between the magnetic field deviation rates of the coil optimized by traditional derivative algorithms within a range of 0.2 m ∼ 0.8 m from the central axis of the magnetic field. Finally, finite element simulation was employed to verify the calculated results. The results show that the magnetic field deviation rate of the coil is less than 0.5% when the intelligent algorithm is used for optimization in the range of 0.6 m from the central axis. In addition, the structure can be extended to a three-dimensional structure, which can achieve a constant magnetic field in any direction by controlling the size and direction of the current, making it a potential application prospect in magnetic navigation technology.

The Sun’s Magnetic Power Spectra over Two Solar Cycles. I. Calibration between SDO/HMI and SOHO/MDI Magnetograms

The Sun’s magnetic field is strongly structured over a broad range of scales. Magnetic spatial power spectral analysis provides a powerful tool for understanding the various scales of magnetic fields and their interactions with plasma motions. We aim to investigate the power spectra using spherical harmonic decomposition of high-resolution Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) and Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) synoptic magnetograms covering three consecutive solar cycle minima, in a series of papers. As the first of the series, we calibrate and analyze the power spectra based on cotemporal SDO/HMI and SOHO/MDI data in this paper. For the first time, we find that the calibration factor r between SOHO/MDI and SDO/HMI varies with the spatial scale l of the magnetic field, where l is the degree of the spherical harmonic. The calibration factor satisfies . With the calibration function, most contemporaneous SOHO/MDI and SDO/HMI magnetograms show consistent power spectra from about 8 Mm to the global scales over about three orders of magnitude. Moreover, magnetic power spectra from SOHO/MDI and SDO/HMI maps show peaks/knees at l ≈ 120, corresponding to the typical supergranular scale (about 35 Mm) constrained from direct velocimetric measurements. This study paves the way for investigating the solar cycle dependence of supergranulation and magnetic power spectra in subsequent studies.

Numerical simulations of the Tayler–Spruit dynamo in proto-magnetars

ABSTRACT The Tayler–Spruit dynamo is one of the most promising mechanisms proposed to explain angular momentum transport during stellar evolution. Its development in proto-neutron stars spun-up by supernova fallback has also been put forward as a scenario to explain the formation of very magnetized neutron stars called magnetars. Using three-dimensional direct numerical simulations, we model the proto-neutron star interior as a stably stratified spherical Couette flow with the outer sphere that rotates faster than the inner one. We report the existence of two subcritical dynamo branches driven by the Tayler instability. They differ by their equatorial symmetry (dipolar or hemispherical) and the magnetic field scaling, which is in agreement with different theoretical predictions (by Fuller and Spruit, respectively). The magnetic dipole of the dipolar branch is found to reach intensities compatible with observational constraints on magnetars.

Time-reversal symmetry breaking in the superconducting low carrier density quasiskutterudite Lu3Os4Ge13

The complex structure of the Remeika phases, the intriguing quantum states they display, and their low carrier concentrations are strong motivations to study the nature of their superconducting phases. In this Letter, the microscopic properties of the superconducting phase of single-crystalline ${\mathrm{Lu}}_{3}{\mathrm{Os}}_{4}{\mathrm{Ge}}_{13}$ are investigated by muon-spin relaxation and rotation ($\ensuremath{\mu}\mathrm{SR}$) measurements. The zero-field $\ensuremath{\mu}\mathrm{SR}$ data reveal the presence of spontaneous static or quasistatic magnetic fields in the superconducting state, breaking time-reversal symmetry; the associated internal magnetic-field scale is found to be exceptionally large ($\ensuremath{\simeq}$ 0.11 mT). Furthermore, transverse-field $\ensuremath{\mu}\mathrm{SR}$ measurements in the vortex state of ${\mathrm{Lu}}_{3}{\mathrm{Os}}_{4}{\mathrm{Ge}}_{13}$ imply a complex gap function with significantly different strengths on different parts of the Fermi surface. Although our measurements do not completely determine the order parameter, they strongly indicate that electron-electron interactions are essential to stabilizing pairing in the system, thus, demonstrating its unconventional nature.

Characteristic Scales of Complexity and Coherence within Interplanetary Coronal Mass Ejections: Insights from Spacecraft Swarms in Global Heliospheric Simulations

Many aspects of the 3D structure and evolution of interplanetary coronal mass ejections (ICMEs) remain unexplained. Here, we investigate two main topics: (1) the coherence scale of magnetic fields inside ICMEs, and (2) the dynamic nature of ICME magnetic complexity. We simulate ICMEs interacting with different solar winds using the linear force-free spheromak model incorporated into the EUHFORIA model. We place a swarm of ∼20,000 spacecraft in the 3D simulation domain and characterize ICME magnetic complexity and coherence at each spacecraft based on the simulated time series. Our simulations suggest that ICMEs retain a lower complexity and higher coherence along their magnetic axis, but that a characterization of their global complexity requires crossings along both the axial and perpendicular directions. For an ICME of initial half angular width of 45° that does not interact with other large-scale solar wind structures, global complexity can be characterized by as little as 7–12 spacecraft separated by 25°, but the minimum number of spacecraft rises to 50–65 (separated by 10°) if interactions occur. Without interactions, ICME coherence extends for 45°, 20°–30°, 15°–30°, and 0°–10° for B, B ϕ , B θ , and B r , respectively. Coherence is also lower in the ICME west flank compared to the east flank due to Parker spiral effects. Moreover, coherence is reduced by a factor of 3–6 by interactions with solar wind structures. Our findings help constrain some of the critical scales that control the evolution of ICMEs and aid in the planning of future dedicated multispacecraft missions.

Lattice distortions and the metal–insulator transition in pure and Ti-substituted Ca3Ru2O7

We report pair distribution function studies on the relationship between the metal–insulator transition (MIT) and lattice distortions in pure and Ti-substituted bilayer Ca3Ru2O7. Structural refinements performed as a function of temperature, magnetic field and length scale reveal the presence of lattice distortions not only within but also orthogonal to the bilayers. Because of the distortions, the local and average crystal structure differ across a broad temperature region extending from room temperature to temperatures below the MIT. The coexistence of distinct lattice distortions is likely to be behind the marked structural flexibility of Ca3Ru2O7 under external stimuli. This observation highlights the ubiquity of lattice distortions in an archetypal Mott system and calls for similar studies on other families of strongly correlated materials.

Diagnosing magnetic fields in cylindrical implosions with oblique proton radiography

Two experiments at the OMEGA Laser System used oblique proton radiography to measure magnetic fields in cylindrical implosions with and without an applied axial magnetic field. Although the goal of both experiments was to measure the magnitude of the compressed axial magnetic field in the core of the implosion, this field was obfuscated by two features in the coronal plasma produced by the compression beams: an azimuthal self-generated magnetic field and small length scale, high-amplitude structures attributed to collisionless effects. In order to understand these features, synthetic radiographs are generated using fields produced by 3D HYDRA simulations. These synthetic radiographs reproduce the features of the experimental radiographs with the exception of the small-scale structures. A direct inversion algorithm is successfully applied to a synthetic radiograph but is only partially able to invert the experimental radiographs in part because some protons are blocked by the field coils. The origins of the radiograph features and their dependence on various experimental parameters are explored. The results of this analysis should inform future measurements of compressed axial magnetic fields in cylindrical implosions.

Magnetovolume Effect on the First-Order Metamagnetic Transition in UTe2

The link between the metamagnetic transition and novel spin-triplet superconductivity of UTe$_2$ was discussed thermodynamically through magnetostriction measurements in a pulsed-magnetic field. We revealed a discontinuous magnetostriction across the metamagnetic transition at $\mu_0H_{\rm m}\approx 35$~T for the applied magnetic fields along the crystallographic $b$ axis in the orthorhombic structure. The resultanting volume magnetostriction of $\Delta V/V \approx-5.9\times 10^{-4}$ gives the initial pressure dependence of $H_{\rm m}$ by employing the Clausius-Clapeyron's equation, which agrees with previous pressure experiments. Further, significant anisotropic magnetostriction (AMS), derived by subtracting the averaged linear magnetostriction, was revealed. Contrary to the weakly field-dependent AMS along the $a$ axis, those along the $b$ and $c$ axes show strong field dependences with a similar magnitude but with opposite signs, indicating its lattice instability. The relationship between characteristic energy scales of magnetic fields and temperatures was discussed in terms of the Gr\"uneisen parameters compared to the other $f$-electron systems. The volume shrinkage in UTe$_2$ at $H_{\rm m}$, contrary to the volume expansion in typical heavy fermion metamagnets, pushes to invoke the link with the valence instability related to the itinerant-localized dual nature of the U magnetism.

Gravitational wave signal from primordial magnetic fields in the Pulsar Timing Array frequency band

The NANOGrav, Parkes, European, and International Pulsar Timing Array (PTA) Collaborations have reported evidence for a common-spectrum process that can potentially correspond to a stochastic gravitational wave background (SGWB) in the 1--100 nHz frequency range. We consider the scenario in which this signal is produced by magnetohydrodynamic (MHD) turbulence in the early Universe, induced by a nonhelical primordial magnetic field at the energy scale corresponding to the quark confinement phase transition. We perform MHD simulations to study the dynamical evolution of the magnetic field and compute the resulting SGWB. We show that the SGWB output from the simulations can be very well approximated by assuming that the magnetic anisotropic stress is constant in time, over a time interval related to the eddy turnover time. The analytical spectrum that we derive under this assumption features a change of slope at a frequency corresponding to the GW source duration that we confirm with the numerical simulations. We compare the SGWB signal with the PTA data to constrain the temperature scale at which the SGWB is sourced, as well as the amplitude and characteristic scale of the initial magnetic field. We find that the generation temperature is constrained to be in the 1--200 MeV range, the magnetic field amplitude must be $>1$\% of the radiation energy density at that time, and the magnetic field characteristic scale is constrained to be $>10$\% of the horizon scale. We show that the turbulent decay of this magnetic field will lead to a field at recombination that can help to alleviate the Hubble tension and can be tested by measurements in the voids of the Large Scale Structure with gamma-ray telescopes like the Cherenkov Telescope Array.

Layer-Dependent Interlayer Antiferromagnetic Spin Reorientation in Air-Stable Semiconductor CrSBr.

Magnetic van der Waals (vdW) materials possess versatile spin configurations stabilized in reduced dimensions. One magnetic order is the interlayer antiferromagnetism in A-type vdW antiferromagnet, which may be effectively modified by the magnetic field, stacking order, and thickness scaling. However, atomically revealing the interlayer spin orientation in the vdW antiferromagnet is highly challenging, because most of the material candidates exhibit an insulating ground state or instability in ambient conditions. Here, we report the layer-dependent interlayer antiferromagnetic spin reorientation in air-stable semiconductor CrSBr using magnetotransport characterization and first-principles calculations. We reveal an odd-even layer effect of interlayer spin reorientation, which originates from the competitions among interlayer exchange, magnetic anisotropy energy, and extra Zeeman energy of uncompensated magnetization. Furthermore, we quantitatively constructed the layer-dependent magnetic phase diagram with the help of a linear-chain model. Our work uncovers the layer-dependent interlayer antiferromagnetic spin reorientation engineered by magnetic field in the air-stable semiconductor.

Signature of a randomness-driven spin-liquid state in a frustrated magnet

Collective behaviour of electrons, frustration induced quantum fluctuations and entanglement in quantum materials underlie some of the emergent quantum phenomena with exotic quasi-particle excitations that are highly relevant for technological applications. Herein, we present our thermodynamic and muon spin relaxation measurements, complemented by ab initio density functional theory and exact diagonalization results, on the recently synthesized frustrated antiferromagnet Li4CuTeO6, in which Cu2+ ions (S = 1/2) constitute disordered spin chains and ladders along the crystallographic [101] direction with weak random inter-chain couplings. Our thermodynamic experiments detect neither long-range magnetic ordering nor spin freezing down to 45 mK despite the presence of strong antiferromagnetic interaction between Cu2+ moments leading to a large effective Curie-Weiss temperature of − 154 K. Muon spin relaxation results are consistent with thermodynamic results. The temperature and magnetic field scaling of magnetization and specific heat reveal a data collapse pointing towards the presence of random-singlets within a disorder-driven correlated and dynamic ground-state in this frustrated antiferromagnet.

Magnetic-Field Universality of the Kondo Effect Revealed by Thermocurrent Spectroscopy.

Probing the universal low-temperature magnetic-field scaling of Kondo-correlated quantum dots via electrical conductance has proved to be experimentally challenging. Here, we show how to probe this in nonlinear thermocurrent spectroscopy applied to a molecular quantum dot in the Kondo regime. Our results demonstrate that the bias-dependent thermocurrent is a sensitive probe of universal Kondo physics, directly measures the splitting of the Kondo resonance in a magnetic field, and opens up possibilities for investigating nanosystems far from thermal and electrical equilibrium.

Magnetic Field and Electron Density Scaling Properties in the Equatorial Plasma Bubbles

The ionospheric plasma density irregularities are known to play a role in the propagation of electromagnetic signals and to be one of the most important sources of disturbance for the Global Navigation Satellite System, being responsible for degradation and, sometimes, interruptions of the signals received by the system. In the equatorial ionospheric F region, these plasma density irregularities, known as plasma bubbles, find the suitable conditions for their development during post-sunset hours. In recent years, important features of plasma bubbles such as their dependence on latitude, longitude, and solar and geomagnetic activities have been inferred indirectly using their magnetic signatures. Here, we study the scaling properties of both the electron density and the magnetic field inside the plasma bubbles using measurements on board the Swarm A satellite from 1 April 2014 to 31 January 2016. We show that the spectral features of plasma irregularities cannot be directly inferred from their magnetic signatures. A relation more complex than the linear one is necessary to properly describe the role played by the evolution of plasma bubbles with local time and by the development of turbulent phenomena.

On viscoelastic transient response of magnetically imperfect functionally graded nanobeams

This research focuses on transient response of porosity-dependent viscoelastic functionally graded nanobeams subjected to dynamic loads and magnetic field as well. The material properties of the nanobeams with changing gradually along thickness direction is presented by modified power-law function. In this research, nonlocal strain gradient theory (NSGT) in framework of a quasi-3D beam theory, which is capable of including thickness stretching effect, are employed. In order to capture the internal damping effect in the model, Kelvin-Voigt visco constitutive model is applied. Applying Hamilton's variation, the governing equations are obtained, and Navier as well as inverse Laplace transform methods are utilized to solve them analytically. Eventually, some parametric investigations are conducted to display the sensitivity of transient response to porosity coefficient, internal damping, volume fraction, length to thickness ratio, position of point load, magnetic field as well as small size parameters. It is manifested that by raising the magnetic field and length scale parameter (LSP), the oscillation amplitudes diminish whereas the number of periodic cycles of the nanobeams increases and the systems are damped much faster.

Magnetic Fields in Star Formation: A Complete Compilation of All the DCF Estimations

Abstract The Davis–Chandrasekhar–Fermi (DCF) method provides an indirect way to estimate the magnetic field strength from statistics of magnetic field orientations. We compile all the previous DCF estimations from polarized dust emission observations and recalculate the magnetic field strength of the selected samples with the new DCF correction factors in Liu et al. We find the magnetic field scales with the volume density as B ∝ n 0.57. However, the estimated power-law index of the observed B–n relation has large uncertainties and may not be comparable to the B–n relation of theoretical models. A clear trend of decreasing magnetic viral parameter (i.e., increasing mass-to-flux ratio in units of critical value) with increasing column density is found in the sample, which suggests the magnetic field dominates the gravity at lower densities but cannot compete with the gravity at higher densities. This finding also indicates that the magnetic flux is dissipated at higher column densities due to ambipolar diffusion or magnetic reconnection, and the accumulation of mass at higher densities may be by mass flows along the magnetic field lines. Both sub-Alfvénic and super-Alfvénic states are found in the sample, with the average state being approximately trans-Alfvénic.

Bistable Valves for MR Fluid-Based Soft Robotic Actuation Systems

Magnetorheological (MR) fluids have unique characteristics that make them well-suited for soft robotic actuation systems. Two particularly interesting applications are bistable valves and force-amplified grippers, which only require power to switch states. These design topologies can not only make MR fluid actuation systems more efficient, but can also allow them to be constructed from entirely compliant materials. In this work, we describe new bistable valve mechanism concepts; the first design is constructed using traditional rigid components while the second design is composed of entirely compliant materials. This includes liquid metal coils, compliant magnetic composites, and silicone flexures. The MR valve concept is modeled using magnetic field theory and scaling laws are determined from MR fluid holding pressure experiments. Then, experimental results are used to show that rough tubing surfaces can withhold an average of 5× more pressure than smooth tubing surfaces. Both rigid and compliant valve topologies are then constructed and tested, showing the ability to hold up to 88 kPa and 37 kPa of pressure, respectively. These valves are then implemented for controlling a soft multi-fingered PneuNet gripper and a new force-amplified MR fluid gripper, which has the ability to provide up to 324$\%$ higher load capacity than purely pressure-driven mechanisms (with the addition of a 25 mm diameter and 12.7 mm thick Nd-Fe-B magnet). Finally, we show how these bistable valves and grippers can be used for grasping and manipulation applications.

Rapid modification of neutron star surface magnetic field: a proposed mechanism for explaining radio emission state changes in pulsars

ABSTRACT The radio emission in many pulsars shows sudden changes, usually within a period, that cannot be related to the steady state processes within the inner acceleration region (IAR) above the polar cap. These changes are often quasi-periodic in nature, where regular transitions between two or more stable emission states are seen. The durations of these states show a wide variety ranging from several seconds to hours at a time. There are strong, small-scale magnetic field structures and huge temperature gradients present at the polar cap surface. We have considered several processes that can cause temporal modifications of the local magnetic field structure and strength at the surface of the polar cap. Using different magnetic field strengths and scales, and also assuming realistic scales of the temperature gradients, the evolutionary time-scales of different phenomena affecting the surface magnetic field were estimated. We find that the Hall drift results in faster changes in comparison to both Ohmic decay and thermoelectric effects. A mechanism based on the partially screened gap (PSG) model of the IAR has been proposed, where the Hall and thermoelectric oscillations perturb the polar cap magnetic field to alter the sparking process in the PSG. This is likely to affect the observed radio emission resulting in the observed state changes.

Coherence scale of magnetic fields generated in early-time forward shocks of GRBs

ABSTRACT We report the earliest ever detection of optical polarization from a GRB forward shock (GRB 141220A), measured $129.5{-}204.3\,$s after the burst using the multicolour RINGO3 optical polarimeter on the 2-m fully autonomous robotic Liverpool Telescope. The temporal decay gradient of the optical light curves from $86\,$ to $\sim 2200\,$s post-burst is typical of classical forward shocks with α = 1.091 ± 0.008. The low-optical polarization $P_{ BV} = 2.8 _{- 1.6} ^{+ 2.0} \, {{\ \rm per\ cent}}$ (2σ) at mean time $\sim 168\,$s post-burst is compatible with being induced by the host galaxy dust ($A_{V, {\rm HG}}= 0.71 \pm 0.15 \,$mag), leaving low polarization intrinsic to the GRB emission itself – as theoretically predicted for forward shocks and consistent with previous detections of low degrees of optical polarization in GRB afterglows observed hours to days after the burst. The current sample of early-time polarization data from forward shocks suggests polarization from (a) the Galactic and host galaxy dust properties (i.e. $P \sim 1-3{{\ \rm per\ cent}}$), (b) contribution from a polarized reverse shock (GRB deceleration time, jet magnetization) or (c) forward shock intrinsic polarization (i.e. $P \le 2{{\ \rm per\ cent}}$), which depends on the magnetic field coherence length-scale and the size of the observable emitting region (burst energetics, circumburst density).

Research on Uniform Magnetic Field Compensation Structure of Array Circular Coils for Wireless Power Transfer

In a wireless charging system, non-alignment has been a big problem that affects the transmission efficiency. The uniform magnetic field can ensure the charging power stability and extension of battery life in a multi-load wireless charging system, which also expands the free charging area of the loads. In this article, the array circular coils of wireless power transfer (WPT) with a compensation structure have been proposed, which can be obtained by analyzing the magnetic field trajectory of the elementary unit of the array coils. Larger scale of the uniform magnetic field could be expended by the joint of several elementary units. The correctness and validity of the structure are verified by theoretical derivation and finite element simulation. Besides, the compensation method could be used for any forms of array coils.