Magnetic Field Response Research Articles

Empirical Modeling of Dayside Magnetic Structures Associated With Polar Cusps

AbstractThe magnetic structure of dayside polar cusps is intimately related to the high‐latitude field‐aligned currents (FACs) and the cross‐B diamagnetic currents due to the penetrated plasma of magnetosheath origin. The dayside FAC configuration is sensitive to the azimuthal component of the interplanetary magnetic field, manifested in the latitudinal splitting and longitudinal overlapping of the Region 1 FAC zone around noon. The diamagnetism of the polar cusp plasma results in deep cleft‐shaped depressions of the ambient magnetic field. Neither of the above factors have yet been properly addressed in the existing empirical models of the distant magnetosphere. To fill this gap, an advanced data‐based model has been developed, including the spiral structure of the dayside FACs and their splitting/overlapping in response to the orientation and magnitude of the azimuthal interplanetary magnetic field component By. The cusp diamagnetic field depressions are modeled using a new approach, based on a 3‐D system of magnetic “bubbles” (Tsyganenko & Andreeva, 2018, https://doi.org/10.1029/2018GL078714). The magnetic effects associated with FACs and diamagnetic currents are represented within the framework of a single hybrid model, fitted to large subsets of spacecraft data. The obtained results are analyzed in the context of the dayside magnetic field response to interplanetary conditions and the geodipole tilt angle.

High sensitivity magnetometer using nanocomposite polymers with large magneto-optic response.

Miniaturized magnetic field sensors are increasingly used in various applications, such as geophysical exploration for minerals and oil, volcanology, earthquake studies, and biomedical imaging. Existing magnetometers lack either the spatial or the temporal resolution or are restricted to costly shielded labs and cannot operate in an unshielded environment. Increasing spatio-temporal resolution would allow for real-time measurements of magnetic fluctuations with high resolution. Here we report on a new nanocomposite-based system for miniaturized magnetic field sensing. The sensor is based on Dy3+-doped magnetite and cobalt ferrite nanoparticles dispersed in a polymer matrix. Operation is feasible at room temperature and in an unshielded environment. A compact fiber-optic interferometer is used as the detection mechanism with 20 fT/√Hz sensitivity. We investigated the magnetic field response of the sensor and demonstrated the measurement of the human heartbeat as a potential application.

Polarization of the spontaneous magnetic field and magnetic fluctuations in s+is anisotropic multiband superconductors

We show that multiband superconductors with broken time-reversal symmetry can produce spontaneous currents and magnetic fields in response to the local variations of pairing constants. Considering the iron pnictide superconductor Ba$_{1-x}$K$_x$Fe$_2$As$_2$ as an example we demonstrate that both the point-group symmetric $s+is$ state and the C$_4$-symmetry breaking $s+id$ states produce in general the same magnitudes of spontaneous magnetic fields. In the $s+is$ state these fields are polarized mainly in ab crystal plane, while in the $s+id$ state their ab-plane and c-axis components are of the same order. The same is true for the random magnetic fields which are produced by the order parameter fluctuations near the critical point of the time-reversal symmetry breaking phase transition. Our findings can be used as a direct test of the $s+is/s+id$ dichotomy and the additional discrete symmetry breaking phase transitions with the help of muon spin relaxation experiments.

OA025] Response of ionization chambers in the presence of magnetic fields

Purpose The next generation of medical electron linear accelerators will integrate Magnetic Resonance Tomography (MRI). Therefore it will be possible to take direct images of the moving tumor during radiotherapy treatment. However serious consideration must be given to the strong magnetic field, which has an impact on the trajectories of the produced secondary electrons, because of the Lorentz force. This force affects both the dose distribution in water and the dose response of used detectors. For an accurate patient dosimetry these effects must be taken into account. Methods Monte Carlo methods correctly describe the radiation transport in different media, even in presence of magnetic fields and are therefore the gold standard for the evaluation of the impact of magnetic fields on clinical dosimetry. In this present study, the beam quality correction factors Kq and the relative response in magnetic fields of different ion chambers (PTW-31013, PTW-31021, EXRADIN-1ASL, NE2571) were investigated with Monte Carlo simulations, using the code EGSnrc. The chambers were modelled in detail according to the information given by the manufacturer and placed in a water phantom (30 × 30 × 30 cm3). The chambers were irradiated under reference conditions, following the recommendations of present dosimetry protocols, such as IAEA TRS-398: i.e. the field size at the phantom surface was 10 × 10cm2; the focus-surface-distance 100 cm and the depth of the chamber’s reference point was 10 cm. The source of the photons were several spectra of clinical medical accelerators applying nominal energies between 4 and 24 MV-X. The magnetic field was applied in different directions relative to the beam axis (z-direction) and the chamber’s symmetry axis and was varied between 0 and 3T. Results All chambers successfully passed the Fano test, the response of all chambers varied up to about 8% depending on the magnetic field strength and the field directions. Conclusions The response of the chambers with the magnetic fields, has a complex dependence on chamber radius, magnetic field strength, the orientation between radiation beams, chamber axis and magnetic field, and lastly the energy spectrum. Those variables consequently played a major role in the increase or decrease of correction factor, Kq.

Confirmation of spatial coexistence of magneto-electric coupling in Bi0.7Dy0.3FeO3 thin films integrated with Si/ZnO film for MEMS and memory applications

Spatial presence of ferroelectric and magnetic domain structure of the multiferroic dysprosium (Dy)-modified BiFeO3 (Bi0.7Dy0.3FeO3 or BDFO) deposited on ZnO at the macroscopic level is investigated in this paper. BDFO thin film is deposited on Si/ZnO using pulsed laser deposition (PLD) technique. Magnetic properties are observed by saturated magnetic hysteresis at room temperature. Ferroelectric hysteresis loop (P–E) is used to compare the response of magnetic field on ferroelectric properties at room temperature of BDFO and BDFO/ZnO thin films. The changes in ferroelectric hysteresis loops with magnetic field ensures about the magnetoelectric (M–E) coupling in BDFO/ZnO films. A well-saturated ferroelectric hysteresis loop with remarkable improvement in remanent polarization (∼1.72μC/cm2) is observed. The obtained results confirm the coexistence of ferromagnetic and ferroelectric ordering with significant coupling at room temperature. The coupling behavior and magnetic transition are also verified using multimode atomic force microscope by applying bias between sample and MFM tip. The leakage current density is measured in the order of 10−5A/cm2. Integration of BDFO films with ZnO piezoelectric thin film suggests in principle its potential in applications of micro electro mechanical systems (MEMS) as well as in memory devices and in strong history dependent systems.

Long-lived-correlated triplet-pair state in an imide substituted poly-thienylene vinylene-based π-conjugated polymer

We report on the photophysical properties of a soluble thienylene-vinylene π-conjugated polymer, namely imide poly-thienylene vinylene. Ultrafast pump probe spectroscopy reveals that a broad photoinduced absorption (PA) band is immediately photogenerated along with a narrower PA from the photoinduced singlet excitons. The broad PA is susceptible to magnetic field and thus is assigned to a correlated triple pair state. This feature shows a long lifetime persisting into the μs time domain, in contrast to the singlet exciton PA, which quickly decays on a 10-ps timescale. The steady-state PA spectrum is identical to the transient PA spectrum of the triplet pair state but shows a magnetic field response that is typical to isolated triplet excitons.

Functionalized chitosan with super paramagnetic hybrid nanocarrier for targeted drug delivery of curcumin

Recently, hydrophobically functionalized polymers have been deployed as carriers to improve the encapsulation of hydrophobic drugs. The metal nanocomposites are extensively used to improve the biocompatibility of the formulation and target the drug to the specialized site. In our current study, naphthalene acetate (NAA) was incorporated into the amine group of chitosan to form a hydrophobically functionalized chitosan–NAA drug delivery carrier. The calcium ferrite nanoparticles (CFNP) were embedded in the chitosan–NAA matrix to form a super paramagnetic hybrid nanocarrier for controlled curcumin drug delivery. Various analytical techniques were performed to ensure the functional group modifications, thermal stability, surface nature and morphological behavior of synthesized hybrid carriers. The maximum encapsulation efficiency of 93.6% was obtained under the optimized conditions of drug to chitosan–NAA at 0.1, CFNP to chitosan–NAA at 0.75 and TPP to chitosan–NAA at 1.0 (w/w) ratios, respectively, by adapting Taguchi method. Drug release studies were conducted to determine the effect of pH, drug loading concentrations and magnetic field responses. The drug release data were fitted to various kinetic release models to understand the drug release mechanism. The biocompatibility of the hybrid material was tested using L929 mouse fibroblast cells. The cytotoxicity test against breast cancer cells (MCF-7) was also performed to study the anticancer property of the hybrid paramagnetic material. The prepared curcumin-loaded chitosan–NAA/CFNP was very active against cancer cells in comparison to the normal cells. The results confirmed the applicability of the hybrid nanocarriers in cancer cell-targeted drug delivery.

Three dimensional fluid-kinetic model of a magnetically guided plasma jet

A fluid-kinetic model of the collisionless plasma flow in a convergent-divergent magnetic nozzle is presented. The model combines the leading-order Vlasov equation and the fluid continuity and perpendicular momentum equation for magnetized electrons, and the fluid equations for cold ions, which must be solved iteratively to determine the self-consistent plasma response in a three-dimensional magnetic field. The kinetic electron solution identifies three electron populations and provides the plasma density and pressure tensor. The far downstream asymptotic behavior shows the anisotropic cooling of the electron populations. The fluid equations determine the electric potential and the fluid velocities. In the small ion-sound gyroradius case, the solution is constructed one magnetic line at a time. In the large ion-sound gyroradius case, ion detachment from magnetic lines makes the problem fully three-dimensional.

Photomechanically Induced Magnetic Field Response by Controlling Molecular Orientation in 9‐Methylanthracene Microcrystals

AbstractA surfactant‐assisted seeded‐growth method is used to form single‐crystal platelets composed of 9‐methylanthracene with two different internal molecular orientations. The more stable form exhibits a photoinduced twisting, as observed previously for 9‐methylanthracene microribbons grown by the floating drop method. However, the newly discovered elongated hexagonal platelets undergo a photoinduced rolling‐up and unrolling. The ability of the rolled‐up cylindrical shape to trap superparamagnetic nanoparticles enables it to be carried along in a magnetic field gradient. The new photoinduced shape change, made possible by a novel surfactant‐assisted crystal growth method, opens up the possibility of using light to modulate the crystal translational motion.

Photomechanically Induced Magnetic Field Response by Controlling Molecular Orientation in 9-Methylanthracene Microcrystals.

A surfactant-assisted seeded-growth method is used to form single-crystal platelets composed of 9-methylanthracene with two different internal molecular orientations. The more stable form exhibits a photoinduced twisting, as observed previously for 9-methylanthracene microribbons grown by the floating drop method. However, the newly discovered elongated hexagonal platelets undergo a photoinduced rolling-up and unrolling. The ability of the rolled-up cylindrical shape to trap superparamagnetic nanoparticles enables it to be carried along in a magnetic field gradient. The new photoinduced shape change, made possible by a novel surfactant-assisted crystal growth method, opens up the possibility of using light to modulate the crystal translational motion.

Synthesis of Iron Oxide/Gold Composite Nanoparticles Using Polyethyleneimine as a Polymeric Active Stabilizer for Development of a Dual Imaging Probe.

The combination of magnetic and plasmonic properties using iron oxide/gold nanocomposite particles is crucial for the development of multimodal molecular imaging probes. In this study, iron oxide/gold composite nanoparticles (NanoIOGs) were synthesized via the on-site reduction of an Au precursor salt by polyethyleneimine (PEI) molecules attached to iron oxide nanoparticles (IONPs), and they were employed in magnetic resonance and dark-field microscope imaging. PEI is considered as a polymeric active stabilizer (PAS), acting as a reducing agent for the synthesis of Au and a dispersant for nanoparticles. When the IONPs prepared at the PEI concentration of 0.02 wt. % were used for the NanoIOG synthesis, Au nanoseeds were formed around the IONPs. The alloy clusters of IONPs/Au crystals were produced with further reduction depending on PEI concentration. The NanoIOGs exhibited superparamagnetism in a magnetic field and plasmonic response in a dark-field (DF) microscope. The sizes, morphologies, magnetizations, and r2 relaxivities of NanoIOGs were affected significantly by the amount of PEI added during the NanoIOG synthesis. It is suggested that the PAS-mediated synthesis is simple and effective, and can be applied to various nanostructured Au-metal alloys.

Magnetic field dependence of photocurrent in thermally evaporated rubrene-based devices

The magnetic field response of photocurrent in thermally evaporated rubrene-based single layer devices was investigated, with the results revealing a change of sign in magneto-photocurrent (MPC) with a change of bias. Specifically, under forward bias, there was a positive MPC for |B| > 50 mT, while otherwise there was a negative MPC at smaller fields, forming a “W” shape at low magnetic fields. In contrast, the sign of the MPC was completely changed under reverse bias, forming an “M” shape at low magnetic fields (|B| < 50 mT). Our study suggests that the observed MPC was not only related to the singlet fission (SF) process itself but also strongly dependent on the subsequent decay routes of triplets in rubrene. The triplet-charge reaction and triplet dissociation superimposed on SF under magnetic fields were proposed to account for the different MPC under forward and reverse bias, respectively. Moreover, the magnitude of both the positive and negative MPC could be promoted by avoiding the triplet loss channel of triplet-triplet annihilation in the rubrene devices.

Spectral characterization of plastic scintillation detector response as a function of magnetic field strength

The purpose of this work was to characterize intensity and spectral response changes in a plastic scintillation detector (PSD) as a function of magnetic field strength. Spectra measurements as a function of magnetic field strength were performed using an optical spectrometer. The response of both a PSD and PMMA fiber were investigated to isolate the changes in response from the scintillator and the noise signal as a function of magnetic field strength. All irradiations were performed in water at a photon beam energy of 6 MV. Magnetic field strengths of (0, ±0.35, ±0.70, ±1.05, and ±1.40) T were investigated. Four noise subtraction techniques were investigated to evaluate the impact on the resulting noise-subtracted scintillator response with magnetic field strength. The noise subtraction methods included direct spectral subtraction, the spectral method, and variants thereof. The PMMA fiber exhibited changes in response of up to 50% with magnetic field strength due to the directional light emission from erenkov radiation. The PSD showed increases in response of up to 10% when not corrected for the noise signal, which agrees with previous investigations of scintillator response in magnetic fields. Decreases in the erenkov light ratio with negative field strength were observed with a maximum change at −1.40 T of 3.2% compared to 0 T. The change in the noise-subtracted PSD response as a function of magnetic field strength varied with the noise subtraction technique used. Even after noise subtraction, the PSD exhibited changes in response of up to 5.5% over the four noise subtraction methods investigated.

Magnetic measurements in electrical prospecting by resistivity methods

The electrical resistivity and induced polarization (IP) methods are widely used in geological mapping, prospecting and exploration of mineral deposits, engineering geology, hydrogeology, archaeology, and geotechnical and environmental applications. Historically, these methods have formed the basis of the electrical prospecting technique. In these methods, a DC or low-frequency AC electrical current is introduced into the earth through a grounded transmitter line. The measured quantity is the electric field. However, if the earth’s resistivity or chargeability changes horizontally, this change gives rise to an anomalous magnetic field, which is studied by the magnetometric resistivity (MMR) and magnetic induced polarization (MIP) methods, respectively. Along with advantages, some shortcomings are inherent in the MMR and MIP techniques. Apparently, the main drawback of these methods is that the magnetic fields of both the transmitter line wire and ground electrodes on the surface are several orders of magnitude greater than the anomalous magnetic field response. This introduces a significant “noise” to magnetic-resistivity data. We investigate the potential of using a circular electric dipole (CED) in magnetometric resistivity techniques. It has been found that the application of a CED, instead of a conventional transmitter line, dramatically enhances the signal-to-noise ratio.

Fast Eddy Current Testing Defect Classification Using Lissajous Figures

In this paper, we present a fast method for classification of defects detected by eddy current testing (ECT). This is done by using defects derived by lab experiments. For any defect, the ECT magnetic field response for different EC-probe’s paths is represented on a complex plane to obtain Lissajous’ figures. Their shapes are described through the use of few geometrical parameters forming a feature vector. Such vectors are used as signatures of the defects detected by the probe at different crossing angles and distances from the defect. The effectiveness of the proposed approach is evaluated by measuring the performances of three machine learning-based classifiers (Naive Bayes, C4.5/J48 Decision Tree, and Multilayer Perceptron neural network), through the following metrics: area under ROC curve, the Matthews correlation coefficient, and F-Measure. The results confirm the usefulness of the proposed approach to defects detection and classification without the need of an overall scanning of the faulty area. So, it is able to minimize the efforts, and, consequently, the cost of an ECT test.

Estimation of the chiral magnetic effect considering the magnetic field response of the QGP medium**Supported by National Natural Science Foundation of China (11747115, 11475068), the CCNU-QLPL Innovation Fund (QLPL2016P01) and the Excellent Youth Foundation of Hubei Scientific Committee (2006ABB036)

The magnetic field plays a major role in searching for the chiral magnetic effect in relativistic heavy-ion collisions. If the lifetime of the magnetic field is too short, as predicted by simulations of the field in vacuum, the chiral magnetic effect will be largely suppressed. However, the lifetime of the magnetic field will become longer when the QGP medium response is considered. We give an estimate of the effect, especially considering the magnetic field response of the QGP medium, and compare it with the experimental results for the background-subtracted correlator H at RHIC and LHC energies. The results show that our method explains the experimental results better at the top RHIC energy than at the LHC energy.

Magnetoresistance in single-electron transistors comprising a superconducting island with ferromagnetic leads

We report electric and magnetic field responses of single-electron transistors (SETs) comprising a superconducting island with ferromagnetic (FM) leads. We fabricated two SETs, one of which had relatively high resistance and the other had relatively low resistance. The SETs had two states for the gate charge: SET-ON or SET-OFF. They also had two states for the FM lead magnetization: parallel (P) or anti-parallel (AP) configuration. Current-voltage characteristics of four SET states (“P & SET-ON,” “P & SET-OFF,” “AP & SET-ON,” and “AP & SET-OFF”) were measured at approximately 0.1 K in a compact dilution refrigerator. Magnetoresistance ratio (MRR) values were obtained for the SET-ON and SET-OFF states, respectively. The higher-resistance SET1 exhibited positive MRR values for all measured bias voltages. The MRR enhancement was confirmed for the SET-OFF state, which agreed well with the co-tunneling model. The lower-resistance SET2, on the other hand, exhibited negative and positive MRR values for higher and lower bias voltage conditions, respectively. The bias voltage for the MRR polarity reversal was changed by the gate voltage. It was also confirmed that the co-tunneling model was partially valid for negative MRR values.

Chiral magnetic currents with QGP medium response in heavy-ion collisions at RHIC and LHC energies

We calculate the electromagnetic current with a more realistic approach in the RHIC and LHC energy regions in the article. We take the partons formation time as the initial time of the magnetic field response of QGP medium. The maximum electromagnetic current and the time-integrated current are two important characteristics of the chiral magnetic effect (CME), which can characterize the intensity and duration of fluctuations of CME. We consider the finite frequency response of CME to a time-varying magnetic field, find a significant impact from QGP medium feedback, and estimate the generated electromagnetic current as a function of time, beam energy and impact parameter.

Supercurrent through MoS2-based electric double-layer transistor sandwiched between conventional superconductors

Transition metal dichalcogenide molybdenum disulphide (MoS2) is a two-dimensional layered crystal, which has a great potential as a flexible semiconductor device. Recently, manifestation of electrically induced superconductivity at the surface of the MoS2-based electric double-layer transistor (MoS2-EDLT) is reported. The superconducting properties, such as the ultra-high upper critical field, give a sign of unconventional spin-valley locking superconducting state. In this study, we aim to realize the coherent connection of the MoS2-EDLT to conventional superconductors Aluminum (Al). Therefore, we first fabricated and evaluated the properties of Al / MoS2-EDLT configuration/Al junction. At T = 18 mK, it is considered that a superconducting current of about 30 pA flows into the Al/MoS2-EDLT/Al junction. We discussed the magnetic field response of this supercurrent.

Li-ion battery ageing model parameter: SEI layer analysis using magnetic field probing

With the growing usage of lithium-ion (Li-ion) batteries in various applications from stationary applications to automotive industries, their ageing mechanism and its influencing factors have become a big concern today. Ageing may be defined as deterioration in the performance of the battery due to irreversible physical and chemical changes like internal resistance rise, electrolyte decompositions, electrodes cracking and solid electrolyte interphase (SEI) modification/growth. The aim of this research article is to study and analyse the behaviour of SEI layer growth at the anode using a novel non-invasive magnetic field probing (MFP). A 3-d model based upon well-known John Newman’s pseudo 2-d approach has been developed in COMSOL Multiphysics®. It is observed that the magnetic field response (MFR) is inversely related to SEI growth. Anode’s state of charge (SoC) response with SEI layer and MFR is also studied.