Weak Magnetic Field Research Articles

Research and simulation of fiber sensor for weak magnetic field detection

Research and simulation of fiber sensor for weak magnetic field detection

Magnetic micromotors crossing lipid membranes.

Nano/micromotors are self-propelled particles that show enhanced motion upon being triggered by a stimulus. Their use in nanomedicine has been widely explored, with special focus on imaging or drug delivery. However, a thorough understanding of the requirements for more efficient locomotion is still lacking. In this paper, we assembled magnetically propelled motors of different sizes (i.e., 0.5, 1 and 4 μm) and surface chemistries (positive charge or PEGylated) and assessed their motion in the presence of giant unilamellar lipid vesicles (GUVs) of varying compositions (zwitterionic, negatively charged and saturated lipids). Unexpectedly, the size does not seem to be the dominating characteristics that governs the ability of the motors to cross lipid membranes. Specifically, the 0.5 μm PEGylated motors have very limited ability to cross the lipid membrane of GUVs due to their non-interacting nature compared to their equally sized positively charged counterparts. Furthermore, membranes made of saturated lipids and, in particular, in combination with a weak magnetic field facilitate motors' crossing, regardless of their size. The results were validated by in-house data-driven statistical analysis that employs experimental data to allow for the identification of individual motor motion in the ensemble when meeting the lipid membranes. Altogether, we provide insight into motor locomotion when they interact with a biological barrier considering both the entire ensemble and the individual motors, which has the potential to support considerations of future motor designs.

Use of Hyperfine Structure of Optically Detected Magnetic Resonance Spectrum of a Single NV-Defect in Diamond in Quantum Sensorics of Weak Magnetic Fields

Use of Hyperfine Structure of Optically Detected Magnetic Resonance Spectrum of a Single NV-Defect in Diamond in Quantum Sensorics of Weak Magnetic Fields

Numerical simulation of magnetic field influence on plasma and electron extraction of electron cyclotron resonance neutralizer

Electron cyclotron resonance (ECR) neutralizer is a key component of electron cyclotron resonance ion thruster (ECRIT) with a diameter of 10 cm, which plays an important role in maintaining the spacecraft potential balance and neutralizing the ions in the plume region. Optimizing magnetic field distribution is an important way to improve the performance of neutralizer. At the same time, the uniformity of the magnetic field and the position of the magnetic trap can affect the magnetic field characteristics, plasma performance, electron extraction process, and beam current. Previous experimental researches showed that the beam current extraction performances of the two ECR neutralizers with different magnetic field uniformity and different magnetic trap locations are significantly different. However, it is difficult to reveal the physical phenomena and causes only through experiments, so numerical simulation is needed. Therefore PIC/MCC codes for the ECR neutralizers with different uniformity of magnetic field and different positions of magnetic trap are established. Under the given electron extraction potential, numerical simulations are accomplished to study electron extraction procedure and analyze its influence on the performance of the neutralizer. The simulation results show that when the magnetic field uniformity is low and the magnetic trap is located upstream of extraction orifice, the migration of electrons from the magnetic trap to the outlet is limited by the magnetic field and the electric field, thus a higher potential energy is needed to extract the electrons. Otherwise, when the magnetic field uniformity is high and the magnetic trap is located at the downstream of extraction orifice, electrons will be more likely to migrate towards the magnet trap. After the electrons reach the magnetic trap, under the action of the anode potential, the external potential is higher, and the external weak magnetic field almost fails to hold these electrons, Therefore a large number of electrons can be extracted at low extraction potential. This research will lay an important foundation for the development of high-performance ECR neutralizer.

Влияние структуры пленок Co – Ni – Fe, полученных электрохимическим осаждением, на магнитные свойства

An analysis of the crystal structure and composition of Co – Ni – Fe films was carried out and the influence of the deposition rate on the conversion of a weak magnetic field into a magnetic induction dB/dH was established. The presence of oxygen on the surface of the films indicates the porosity of the structure of the Co – Ni – Fe films, which is confirmed by the roughness of the morphology. Electrochemical deposition from a chloride electrolyte showed the possibility of controlling the magnetic properties of films while improving the deposition method. Chloride electrolyte with filtration, additives of boric acid, saccharin and hydrochloric acid at a ratio of concentrations CCo:CNi:CFe = 1: 1: 1 with a temperature of 70 °C provides reproducible electrochemical deposition of Co – Ni – Fe films with low mechanical stresses, with a uniform structure and with a high gain of a weak magnetic field in magnetic induction.

Surface acoustic wave-spin wave coupling and magneto-acoustic nonreciprocal devices

Surface acoustic wave (SAW) is a new means of exciting and controlling spin wave (SW), which has not only high excitation efficiency, but also long transmission length up to millimeter order. Based on the SAW-SW coupling (phonon-magnon coupling), a wide variety of new devices and applications such as high-sensitivity weak magnetic field sensors, energy-efficient spintronic devices, solid-state acoustic isolators, and nonreciprocal phase shifters, have been realized. Therefore, it is of great value to study the physical mechanism of magneto-acoustic coupling, develop new magneto-acoustic coupling effects, and improve the efficiency of magneto-acoustic coupling. In this work, different types of physical mechanisms of magneto-acoustic coupling are reviewed. The effective driven magnetic fields of magnetoelastic coupling, spin-vorticity coupling (including injection of alternating spin current from a non-magnetic layer and Barnett effect inside magnetic material itself), and magneto-rotation coupling under different modes of SAW excitation are compared. The angular dependence of these driven fields and the frequency dependence of the corresponding power absorption are discussed, which provides theoretical support for distinguishing and utilizing various magneto-acoustic coupling in practical applications. In addition, we also introduce two methods to realize nonreciprocal SAW transmission by magneto-acoustic coupling, including the helicity mismatch effect and nonreciprocal spin-wave dispersion magnetic structures, and discuss their physical mechanisms as well as advantages and disadvantages. For such magneto-acoustic nonreciprocal devices, the properties of higher isolation, lower insertion loss and wider bandwidth are always desired. In order to improve the properties of the devices, it is important to find magnetic structures with stronger SW nonreciprocity, reduce the insertion loss introduced by magnetic structure, and fully consider the effective driven field characteristics of different modes of SAW. We hope that this review can serve as a guide for future design and development of solid acoustic isolators and circulators in the RF and microwave frequency bands.

Enhanced measurement precision with continuous interrogation during dynamical decoupling

Dynamical decoupling (DD) is normally ineffective when applied to DC measurement. In its straightforward implementation, DD nulls out DC signal as well while suppressing noise. This work proposes a phase relay method that is capable of continuously interrogating the DC signal over many DD cycles. We illustrate its efficacy when applied to the measurement of a weak DC magnetic field with an atomic spinor Bose–Einstein condensate. Sensitivities approaching standard quantum limit or Heisenberg limit are potentially realizable for a coherent spin state or a squeezed spin state of 10000 atoms, respectively, while ambient laboratory level noise is suppressed by DD. Our work offers a practical approach to mitigate the limitations of DD to DC measurement and would find other applications for resorting coherence in quantum sensing and quantum information processing research.

Influence of the magnetic field and the mean flow configuration on spatial structure and growth rate of normal modes

The first part of the work presents the results of numerical experiments with the magnetohydrodynamic model of “shallow water” to assess the degree of influence of the magnetic field on the development of instabilities conditioned by a combination of inhomogeneities in the mean flow and the mean magnetic field. Normal mode calculations have confirmed the earlier obtained result on the different influence of weak and strong magnetic fields on the instability of differential rotation. Calculations have shown that a weak magnetic field stabilizes the development of instabilities, whereas a strong magnetic field, on the contrary, enhances the instability. Azimuthal inhomogeneities of differential rotation in all cases contribute to the development of instabilities. In the second part of the work, we examine the spatial structure of normal modes and make an attempt to interpret the torsional oscillations observed in the atmospheres of Earth and the Sun. Calculations have shown that regular axisymmetric disturbances can be caused by the formation of a cyclonic vortex above the pole, which is characteristic of Earth's atmosphere and, possibly, of the Sun's atmosphere. The least damped normal mode of a stable polar cyclone has a structure of torsional oscillations. Flow anomalies and the development of an anticyclonic eddy in winter at midlatitudes destroy torsional oscillations and lead to a rapid amplification of normal modes, which are more complex in structure.

Magneto-thermo-gravitational Rayleigh–Bénard convection of an electro-conductive micropolar fluid in a square enclosure: Finite volume computation

This article presents both a theoretical and a numerical analysis of thermo-gravitational magnetic convection in electro-conductive Eringen micropolar fluids in a two-dimensional enclosure. The computational regime is bound with cold top, hot bottoms, and adiabatic side walls. The governing equations were transformed via scaled variables into dimensionless partial differential equations. A Finite volume method (FVM) is used to get a solution of the computational regime. Validation of the FVM solutions is included for non-magnetic special case from the literature. Streamline contours, isotherm contours, iso-microrotation contours (lines of constant angular velocity) and local Nusselt number at the left hot wall is depicted graphically for the impact of Hartmann (magnetic) number (Ha), Prandtl number (Pr), micropolar parameter (K) and Rayleigh number (Ra). A significant modification in internal circulation and micro-rotation in addition to temperature distribution is observed with increasing vortex viscosity parameter. Significant warping of isotherms is induced with stronger magnetic field and the mushroom-shaped core structure encountered at weak magnetic field transitions to a sigmoidal topology.

A dual-wavelength demodulation-based sensor for magnetic fields

This work presents a magnetic field sensor based on a Fabry–Perot interferometer (FPI) doped with a magnetic fluid. The FPI consists of multiple reflective end surfaces. The tail end of the FPI is wrapped with a magnetic fluid, and the external magnetic field adjusts the complex refractive index of the magnetic fluid, which influences the reflectivity of the tail end face of the interferometer and influences the spectral interferogram. The sensor possesses a small size, ease of fabrication, and potential for multiplexing. Additionally, a dual-wavelength intensity demodulation method is employed, which reduces the system cost compared to the spectrometer measurements approach. The measurement accuracy can achieve a value of 2.62 Gs under weak magnetic fields. According to the experimental results, the measurement range can span from 0 to 150 Gs, with a sensitivity of 4.58×10−5 mw/mT.

Влияние магнитного поля и конфигурации среднего течения на пространственную структуру и скорость роста нормальных мод

The first part of the work presents the results of numerical experiments with the magnetohydrodynamic model of “shallow water” to assess the degree of influence of the magnetic field on the development of instabilities conditioned by a combination of inhomogeneities in the mean flow and the mean magnetic field. Numerical simulation of normal modes has confirmed the earlier obtained result on the different influence of weak and strong magnetic fields on the instability of differential rotation. Calculations have shown that a weak magnetic field stabilizes the development of instabilities, whereas a strong magnetic field, on the contrary, enhances the instability. Azimuthal inhomogeneities of differential rotation in all cases contribute to the development of instabilities. In the second part of the work, we examine the spatial structure of normal modes and make an attempt to interpret the torsional oscillations observed in the atmospheres of Earth and the Sun. Calculations have shown that regular axisymmetric disturbances (torsional oscillations) can be caused by the formation of a cyclonic vortex above the pole, which is characteristic of Earth’s atmosphere and, possibly, of the Sun’s atmosphere. The least damped normal mode of a stable polar cyclone has a structure of torsional oscillations. Flow anomalies and the development of an anticyclonic eddy in winter at midlatitudes destroy torsional oscillations and lead to a rapid amplification of normal modes, which are more complex in structure.

Reduction of power loss in easy-plane FeSi soft magnetic composite under a weak bias magnetic field

This paper investigates the impact of a weak bias magnetic field (Hbias) along the easy magnetization plane direction on the power loss of easy-plane Fe-6.5 wt%Si (FeSi) soft magnetic composite (SMC). The results demonstrate that the power loss (Pcv) decreases by 18 % when the Hbias is 11.6 kA/m. Furthermore, it is found that the reduction in Pcv is not only attributed to decreases in hysteresis loss but also involves a decrease in excess loss. The causes of hysteresis loss and excess loss reduction are further investigated and it is found that the effect of the Hbias on the magnetization state plays an important role in the reduction of hysteresis loss. Additionally, the decrease in excess loss can be attributed to the reduction in local eddy current losses caused by non-uniform domain wall motion. These findings provide valuable insights for achieving high-frequency (MHz), high-efficiency, and miniaturized power electronic devices.

Wiedemann-Franz law in graphene in the presence of a weak magnetic field

Wiedemann-Franz law in graphene in the presence of a weak magnetic field

Vortex Dynamics in Superconducting MoN Strip with a Side Cut

Transport characteristics of superconducting MoN strips with a single side cut near one of the superconductor edges in zero and weak magnetic fields are studied experimentally and theoretically. The presence of the cut makes it possible to observe regimes with one and several simultaneously moving Abrikosov vortices, the number of which is controlled by the value of the applied current. A change in the number of vortices is accompanied with the emergence of a “kink” on the current–voltage characteristic, which can be clearly distinguished in the dependence of the differential resistance on the current. This makes it possible to find average velocityv¯of vortices (including a single vortex) and the current/voltage ranges with the known number of moving vortices. The vortex velocity determined in this way for our superconducting strips turns out to be weakly depending on the current and is close to maximal valuev¯max≈ 3 km/s, for which a superconductor transition to the normal state occurs. The maximal velocity value is comparable with the known values for superconductors of types Nb, NbN as well as, and YBCO, but is several times smaller than for superconductors of types MoSi, NbC, and Pb. The fact that difference in the maximal velocities of vortices is associated with different times of variation of the superconducting order parameter magnitude in different superconducting materials is considered.

Pinning of a Magnetic Flux in Polycrystalline YBa<sub>2</sub>Cu<sub>3</sub>O<sub>6.92</sub> HTSC during Cooling in a Weak Magnetic Field

The behavior of fine-grained YBa2Cu3O6.92HTSCs during cooling in a weak magnetic field is investigated. The magnetization of samples, the crystallite sizes is which are comparable with the magnetic field penetration depth, is comprehensively analyzed in the range below the superconducting transition temperature. When the crystallite size is smaller than 0.5 μm, vortices are shown not to be fixed to pinning centers, and the temperature dependence of magnetization is completely determined by the screening of crystallites and the temperature of appearance of intercrystallite superconducting currents.

Magnitouprugost' yan-tellerovskoy podsistemy v kristallakh tipa AIIBVI, dopirovannykh khromom

The influence of an external magnetic field on the complex elastic moduli of crystals with a sphalerite or zinc blende (ZnSe) and wurtzite (CdSe) structure lightly doped by Cr2+ ions has been investigated. Measurements have been performed in the frequency interval 26–32 MHz at 1.4 K. In II–VI crystals, bivalent chromium cations are triply orbital-degenerate in the ground state and, being in a tetrahedral environment, produce Jahn–Teller complexes. These complexes are described in terms of the T ⊗ (e + t2)-problem and exhibit the adiabatic potential energy surface with the global minima of tetragonal symmetry. It has been found that in ZnSe:Cr2+ crystals, a magnetic field directed along the [001] and [110] axes influences modulus (c11 – c12)/2 and does not influence modulus c44. In CdSe:Cr2+ crystals, however, moduli c55 and c66, which are the analogs of (c11 – c12)/2 and c44, depend on the magnetic field directed along the [101¯0101¯0] and [21¯1¯021¯1¯0] axes, respectively. The discovered anomalous behavior of the elastic moduli with magnetic field has been treated in terms of a model that takes into account the crystal field, vibronic and spin-orbital interactions, and the contribution of the Jahn–Teller subsystem to isothermal moduli determined at a constant magnetic induction. Good agreement with experimental dependences of the elastic moduli in strong magnetic fields has been obtained, and it has been shown that the nonmonotonic variation in weak magnetic fields (below 2 T) should be associated with a magnetic field dependence of the relaxation time.

Fast nuclear-spin gates and electrons-nuclei entanglement of neutral atoms in weak magnetic fields

Fast nuclear-spin gates and electrons-nuclei entanglement of neutral atoms in weak magnetic fields

NuSTAR and XMM-Newton observations of the binary 4FGL J1405.1–6119

Context. 4FGL J1405.1−6119 is a high-mass γ-ray-emitting binary that has been studied at several wavelengths. The nature of this type of binary is still under debate, with three possible scenarios usually invoked to explain the origin of the γ-ray emission: collisions between the winds of a rapidly rotating neutron star and its companion, collisions between the winds of two massive stars, and nonthermal emission from the jet of a microquasar. Aims. We analyzed two pairs of simultaneous NuSTAR and XMM-Newton observations to investigate the origin of the radio, X-ray, and γ-ray emissions. Methods. We extracted light curves between 0.5 and 78 keV from two different epochs, which we call Epoch 1 and Epoch 2. We then extracted and analyzed the associated spectra to gain insight into the characteristics of the emission in each epoch. To explain these observations, along with the overall spectral energy distribution, we developed a model of a microquasar jet. This allowed us to make some inferences about the origin of the observed emission and to discuss the nature of the system. Results. A power-law model combined with the inclusion of a blackbody accurately characterizes the X-ray spectrum. The power-law index (E−Γ) was found to be ∼1.7 for Epoch 1 and ∼1.4 for Epoch 2. Furthermore, the associated blackbody temperature was ∼1 keV and with a modeled emitting region of size ≲16 km. The scenario we propose to explain the observations involves a parabolic, mildly relativistic, lepto-hadronic jet. This jet has a compact acceleration region that injects a hard spectrum of relativistic particles. The dominant nonthermal emission processes include synchrotron radiation of electrons, inverse Compton scattering of photons from the stellar radiation field, and the decay of neutral pions resulting from inelastic proton-proton collisions within the bulk matter of the jet. These estimates are in accordance with the values of a super-Eddington lepto-hadronic jet scenario. The compact object could be either a black hole or a neutron star with a weak magnetic field. Most of the X-ray emission from the disk could be absorbed by the dense wind that is ejected from the same disk. Conclusions. We conclude that the binary 4FGL J1405.1−6119 could be a supercritical microquasar similar to SS 433.

Circularly Polarized Electroluminescence of InGaAs/GaAs/CoPt Spin Light Emitting Diodes Placed in a Strong and Weak Magnetic Field

Circularly Polarized Electroluminescence of InGaAs/GaAs/CoPt Spin Light Emitting Diodes Placed in a Strong and Weak Magnetic Field

Effects of static magnetic field on the sulfate metabolic pathway involved in Magnetospirillum magneticum AMB-1 cell growth and magnetosome formation.

Magnetotactic bacteria (MTB) can use their unique intracellular magnetosome organelles to swim along the Earth's magnetic field. They play important roles in the biogeochemical cycles of iron and sulfur. Previous studies have shown that the applied magnetic fields could affect the magnetosome formation and antioxidant defense systems in MTB. However, the molecular mechanisms by which magnetic fields affect MTB cells remain unclear. We aim to better understand the dark at 28°C-29°C for 20 h, as shownthe interactions between magnetic fields and cells, and the mechanism of MTB adaptation to magnetic field at molecular levels. We performed microbiological, transcriptomic, and genetic experiments to analyze the effects of a weak static magnetic field (SMF) exposure on the cell growth and magnetosome formation in the MTB strain Magnetospirillum magneticum AMB-1. The results showed that a 1.5 mT SMF significantly promoted the cell growth but reduced magnetosome formation in AMB-1, compared to the geomagnetic field. Transcriptomic analysis revealed decreased expression of genes primarily involved in the sulfate reduction pathway. Consistently, knockout mutant lacking adenylyl-sulfate kinase CysC did no more react to the SMF and the differences in growth and Cmag disappeared. Together with experimental findings of increased reactive oxidative species in the SMF-treated wild-type strain, we proposed that cysC, as a key gene, can participate in the cell growth and mineralization in AMB-1 by SMF regulation. This study suggests that the magnetic field exposure can trigger a bacterial oxidative stress response involved in AMB-1 growth and magnetosome mineralization by regulating the sulfur metabolism pathway. CysC may serve as a pivotal enzyme in mediating sulfur metabolism to synchronize the impact of SMF on both growth and magnetization of AMB-1.