Variation Of External Magnetic Field Research Articles

Giant magneto-impedance effect in amorphous CoP@Cu microstrip based device in a wide frequency range

The giant magneto-impedance effect (GMI) consists in a large variation in the electrical impedance that occurs in some magnetic materials when subjected to a variable external magnetic field. Here we present an experimental study of the GMI in a wide frequency range observed in a structure of the metallic amorphous magnetic alloy CoP electrodeposited on copper microwires by using a microstrip configuration. In the low frequency range, the magnetic field dependence of the impedance is due to the behavior of the circumferential ac susceptibility in the magnetic coating. In the microwave range the behavior of the GMI is dominated by the main dynamical magnetic phenomenon at high frequencies, namely ferromagnetic resonance (FMR). The experimental data are well fit by Kittel equation for the FMR frequency for a ferromagnetic layer with a saturation magnetization similar to the ones reported in previous works. The structural stability of the CoP alloy against aging effects was also investigated. The overall results indicate that the CoP alloy is a good candidate for applications in sensors and in microwave devices.

Magnetoplasmonic Metasurface-Modulated Electrochemiluminescence Strategy for Extracellular Vesicle Detection.

Due to the ideal optical manipulation ability, the metasurface has broad prospects in the development of novel optical research. In particular, an active metasurface can control optical response through external stimulus, which has attracted great research interest. However, achieving effective modulation of the optical response is a significant challenge. In this work, we have developed a novel electrochemiluminescence (ECL) signal modulation strategy by an active magnetoplasmonic metasurface under an external magnetic field. The magnetoplasmonic metasurface was assembled based on yolk-shell Fe3O4@Au nanoparticles (Fe3O4@Au YS-NPs). On the one hand, the yolk-shell structure of Fe3O4@Au YS-NPs possessed the surface plasmon coupling effect and cavity-based Purcell effect, which provided high-intensity electromagnetic hot spots in the magnetoplasmonic metasurface. On the other hand, due to the strong magnetic response of the Fe3O4 core, the local magnetic field was induced by the external magnetic field, which further generated Lorentz force acting on the free electrons of Au nanoshells with strong optical anisotropy. The plasmon frequency of the metasurface can be effectively modulated by the Lorentz force effect. As a result, the ECL signal of nitrogen dots (N dots) was dynamically modulated and significantly enhanced at a specific polarization angle by the magnetoplasmonic metasurface under the variable external magnetic field. Based on the luminescence modulation ability and structure feature, the magnetoplasmonic metasurface was further established successfully as a sensing interface for gastric cancer (GC) extracellular vesicle (EV) detection. This study illustrated that the electromagnetic response of the active metasurface can effectively improve the optical modulation ability and luminescence sensing performance.

Optical-pump-terahertz-probe spectroscopy in high magnetic fields with kHz single-shot detection.

We demonstrate optical pump-THz probe (OPTP) spectroscopy with a variable external magnetic field (0-9T), in which the time-dependent THz signal is measured by echelon-based single-shot detection at a repetition rate of 1kHz. The method reduces data acquisition times by more than an order of magnitude compared to conventional electro-optic sampling using a scanning delay stage. The approach illustrates the wide applicability of the single-shot measurement approach to non-equilibrium systems that are studied through OPTP spectroscopy, especially in cases where parameters such as magnetic field strength (B) or other experimental parameters are varied. We demonstrate the capabilities of our measurement by performing cyclotron resonance experiments in bulk silicon, where we observe B-field-dependent carrier relaxation and distinct relaxation rates for different carrier types. We use a pair of economical linear array detectors to measure 500 time points on each shot, offering an equivalent performance to camera-based detection with possibilities for higher repetition rates.

The Effect of Substitution of Mn by Pd on the Structure and Thermomagnetic Properties of the Mn1-xPdxCoGe Alloys (Where x = 0.03, 0.05, 0.07 and 0.1).

In the present paper, the influence of partial substitution of Mn by Pd on structure, thermomagnetic properties, and phase transitions in the MnCoGe alloys was investigated. The studies of phase constitution revealed an occurrence of the orthorhombic TiNiSi-type and hexagonal Ni2Ti- type phases. Deep analysis of the XRD pattern supported by the Rietveld analysis allowed us to notice the changes in lattice parameters and quantity of recognized phases depending on the Pd content. An increase of palladium in alloy composition at the expense of manganese induced a rise in the Curie temperature. The values of ΔSM measured for the variation of external magnetic field ~5 T equaled 8.88, 23.99, 15.63, and 11.09 for Mn0.97Pd0.03CoGe, Mn0.95Pd0.05CoGe, Mn0.93Pd0.07CoGe, and Mn0.9Pd0.1CoGe alloy, respectively. The highest magnetic entropy change ΔSM was observed for samples with Pd content x = 0.05 induced by magnetostructural transformation. The analysis of the n vs. T curves allowed confirmation of the XRD and DSC results of an occurrence of the first-order magnetostructural transition in Mn0.95Pd0.05CoGe and Mn0.93Pd0.07CoGe alloys samples.

Exploring the Relationship between Geomagnetic Variations and Seismic Energy Release in Proximity to the Vrancea Seismic Zone

Understanding the seismo–ionospheric coupling mechanism requires a quiet geomagnetic condition, as this represents an ideal situation to detect abnormal variations in the geomagnetic field. In reality, continuous interactions between solar wind and Earth’s magnetosphere create many fluctuations in the geomagnetic field that are more related to sun–magnetosphere interactions than to seismotectonic causes. A triaxial magnetometer was installed at the Muntele Rosu Observatory near the Vrancea seismic zone in 1996 to measure the local magnetic field. Since 2002, the data have become more consistent, allowing for the representation of long time series. Since then, variations have been observed on the eastern component (By) of the magnetic field, which sometimes overlaps with significant earthquakes. Previous studies have shown that high decreases in amplitude recorded on the By component of the magnetic field measured at Muntele Rosu have been accompanied by higher seismicity, while small decreases have been accompanied by lower seismic energy release. This research analyzes the geomagnetic data collected between September 2002 and May 2008 from two geomagnetic observatories, one located in the proximity of the Vrancea seismic zone and another one situated 120 km away. For each geomagnetic anomaly identified, the daily seismic energy released was plotted logarithmically, along with seismicity and Kp indices. Additionally, the daily seismic energy released was also plotted logarithmically for all earthquakes with Mw ≥3. To identify variations in the By component, datasets recorded at Muntele Rosu (MLR) were compared with those recorded at Surlari National Geomagnetic Observatory (SUA), to discriminate between global magnetic variations associated with solar activity and possible seismo–electromagnetic variations. The standard deviation (SDBy) was calculated for each anomaly recorded on the By component of the magnetic field and compared with the cumulative seismic energy release. To determine if this type of variation was present in other components of the magnetic field, the following ratios were calculated for all data recorded at Muntele Rosu: Bz/Bx, Bz/By, and Bz/BH. The size of the anomalies resulting from the standard deviation measured on the By component (SDBy) partially validates the relationship between the size of the anomalies and the seismic energy release during the anomaly. The relationship between the released seismic energy and the anomaly magnitude is vaguely respected, but these variations seem to follow two patterns. One pattern is described by smooth decreases, and the other pattern involves decreases where the By component varies significantly over short periods, generating decreases/increases in steps. It was noticed that seismic activity is greater for the second pattern. Additionally, using standard deviation measured on the magnetic field represents a great tool to discriminate external magnetic field variations from local, possibly seismo–magnetic variations.

Thermal stability of 6-filament MgB2 wire with resistive CuNi sheath cooled by liquid He and water ice

In this paper, thermal stability of two 6-filament MgB2 wires with resistive CuNi sheath has been examined by DC transport measurements at the temperature of liquid He and variable external magnetic fields, and at variable temperatures of water ice under self-field conditions. Current-voltage characteristics up to the quench were performed and the operation limits of both wires under different cooling are analyzed and compared. The obtained results show that only 6 % of well conducting copper core allows to improve the thermal stability considerably, and it also limits the wire heating after the quench. MgB2 wires showed more stable operation after the quench under subcooled water ice in comparison to traditional Helium bath cooling, which offer a cheap and safe cooling mode for future devices.

Theoretical analysis of low frequency dust cyclotron waves with dust charge variations

The propagation of nonlinear dust cyclotron (DC) cnoidal waves having superthermal distributed electrons and ions in the presence of external magnetic field and adiabatic dust charge variation is investigated. The effect of dust charge variation is profoundly modified due to the presence of the superthermal electrons and ions. The dust charge variation parameter decreases with an increase in the superthermality index of ions. Adopting the reductive perturbation approach, it is shown that the dynamics of the cnoidal structure is modeled by a Korteweg–de Vries equation. It is found that only negative potential DC cnoidal and solitary structures are observed in such a plasma. The results further reveal that the cnoidal structures strongly depend on the degree of superthermality, dust charge variation parameter, temperature and number density of fluid particles, angle of obliqueness, as well as on the magnetic field strength. The numerical results confirm that as the dust charge variation enters the picture, amplitude as well as the width of the cnoidal waves enhances. Furthermore, the analysis is performed through Sagdeev potential, plane phase plot and spatial variation of potential to elucidate various aspects of the cnoidal wave dynamics in the presence of the adiabatic dust charge variation.

Pseudo-Qutrit Formed by Two Interacting Identical Spins (s = 1/2) in a Variable External Magnetic Field.

An analytical solution is obtained for the problem of two interacting, identical but separated spin 1/2 particles in a time-dependent external magnetic field, in a general case. The solution involves isolating the pseudo-qutrit subsystem from a two-qubit system. It is shown that the quantum dynamics of a pseudo-qutrit system with a magnetic dipole-dipole interaction can be described clearly and accurately in an adiabatic representation, using a time-dependent basis set. The transition probabilities between the energy levels for an adiabatically varying magnetic field, which follows the Landau-Majorana-Stuckelberg-Zener (LMSZ) model within a short time interval, are illustrated in the appropriate graphs. It is shown that for close energy levels and entangled states, the transition probabilities are not small and strongly depend on the time. These results provide insight into the degree of entanglement of two spins (qubits) over time. Furthermore, the results are applicable to more complex systems with a time-dependent Hamiltonian.

Development of a Magnonic-Based Magnetic Sensor: Comparison of Two Different Implementations With YIG Material

In a ferromagnetic material exposed to a strong magnetic field, the spin wave describes the propagation of the phase shift of precessing spins at the same frequency over the time. In recent years, this subject has been of a great interest in the field of instrumentation and data transmission. Although several studies have shown a strong potential of magnonics for the design of a magnetic field sensor, few studies have been interested in the realization of such sensors and are limited to the measurement of scattering parameters. Here, we describe the development of a magnetic field sensor, using the variations in the propagation of the spin wave induced by the external magnetic field variation. We detailed the full implementation of the system, based on magnonics devices along with its associated electronic. The proposed implementation is mainly based on a quadrature I/Q demodulation to produce an output signal whose variations reflect the variations of the external applied magnetic field. The sensing element is designed from a yttrium iron garnet (YIG) film deposited on the gadolinium gallium garnet (GGG) substrate. It is placed on an optimized microstrip antenna transducer made of two copper lines, respectively, to excite and measure the spin waves. With the help of characterization measurements (S-parameters) carried out with a VNA, field sensitivities, expressed in V/T, could be estimated from S-parameters. Two kinds of magnonic devices have been implemented: one using spin-wave reflections at each YIG edge and other one using spacial filtering by YIG material microstructuring. Their performances regarding the magnetic sensitivity are compared. Finally, this first implementation of such a sensor, based on YIG magnonic material, exhibits a magnetic noise level of about 100 pT/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz at 1 kHz and a usable bandpass of 100 kHz. This is quite promising for a new sensor technology, leaving room for further developments.

Realization and Tests of Prototype Fluxgate Magnetic Sensors for the ITER Neutral Beam Injectors.

In the ITER neutral beam injectors (NBI), the presence of an external variable magnetic field generated by the ITER tokamak itself, could deflect the ion beam during acceleration and cause a loss of beam focusing. For this reason, the ion source, the accelerator and the neutralizer will be shielded from external magnetic field by means of a passive magnetic shield and a system of active correction and compensation coils (ACCC). The ACCC will operate in a feedback control loop and thus require the measurement of magnetic field inside the NBI vessel. Magnetic sensors for this application must be capable of measuring DC and slow variable magnetic fields, and be vacuum-compatible, radiation-hard and robust, since they will be subjected to neutron flux produced by fusion reactions in the tokamak and inaccessible for maintenance. This paper describes the realization and tests of fluxgate magnetic sensors prototypes specifically designed for this purpose before the installation in MITICA and ITER.

Magnetic force microscopy study of induced magnetism in graphene nanoribbons influenced by magnetic nanoparticles

Nanoscale analysis of magnetic properties of graphene nanoribbons (GNRs) conjugated with magnetic nanoparticles has been studied in this work. The effect of varying concentrations of Fe3O4 and Ni nanoparticles on the magnetic domain structure of GNRs has been investigated using magnetic force microscopy (MFM). A variable external magnetic field was applied to the samples, and an evident variation in the domain structure with a change in the magnetic field was observed. It was found that magnetic properties and the imaged magnetic domain structure are influenced by the concentration of magnetic nanoparticles conjugated with GNRs. The vibrating sample magnetometry (VSM) studies support the nano-domain studies done using MFM such that the trend observed for the saturation magnetization obtained from vibrating sample magnetometry (VSM) matches that of the phase difference obtained using MFM.

Investigation of the Behavior of a Photovoltaic Cell under Concentration as a Function of the Temperature of the Base and a Variable External Magnetic Field in 3D Approximation

Investigation of the Behavior of a Photovoltaic Cell under Concentration as a Function of the Temperature of the Base and a Variable External Magnetic Field in 3D Approximation

The effects of nanoparticle percentages and an external variable magnetic field on the atomic and thermal behaviors in an oscillating heat pipe via molecular dynamics simulation

• An OHP is a two-phase heat transfer device with a high effective thermal conductivity. • Using the MD simulation method, this work investigates the atomic and thermal behaviors of nanofluid in an OHP. • A variable external magnetic field is applied to the simulated studied structure. • As the amplitude increases (1 T to 5 T), the HF increases to the maximum value. • The presence of an external field improves the thermal performance in an OHP. In today’s world, heat transfer is a phenomenon that occurs in many important industrial processes. Due to its heat transfer properties and ability to enhance thermal conductivity, nanofluid is a contender for an oscillating heat pipe (OHP). This paper studies the atomic and thermal properties of Fe 3 O 4 /water nanofluid in an OHP with copper (Cu) walls using molecular dynamics (MD) simulations. Thus, the effects of different percentages of Fe 3 O 4 nanoparticles on the density, velocity, temperature profiles, and heat flux (HF) are investigated after 20 ns. The results show as the nanoparticles percentages increase from 1% to 4%, HF value increases from 1561 W/m 2 to 1602 W/m 2, and maximum velocity decreases from 0.044 to 0.038 (Å /ps). The effects of a magnetic field on the density, temperature, velocity and heat transfer profiles were investigated. As the magnetic field amplitude increases (1 T to 5 T), HF increases to the maximum value (1603 W/m 2 ). Besides, as the applied magnetic field increases from 1 T to 5 T, the maximum velocity and temperature increase from 0.048 (Å /ps) and 451 K to 0.068 (Å /ps) and 492 K, respectively, but the maximum density decreases from 0.021 to 0.017 (atom/ Å 3 ). The presence of an external field enhances the thermal performance of the nanofluid in an OHP, hence increasing its use in electronic systems. This study enhances OHPs' thermal behaviour and heat transmission in nanofluids, making them more suitable for medical and industrial applications.

Probability density of irradiance for electromagnetic waves propagating through turbulent magnetized plasma

SummaryNumerous physical mediums can be modelled as turbulent magnetized plasma, for example, the solar corona, and the ionosphere. Scintillation effects on the intensity of electromagnetic beam wave propagating through magnetized plasma necessitate the introduction of a statistical distribution valid over a large range of scintillation conditions, and incorporating the plasma physical properties. Under some simplifying assumptions, such a theoretical model can be derived based on the Rytov solution, the external magnetic field variation, and the space permeating plasma electron density variation. The resultant wave intensity distribution is compared with the Lognormal, Rician, and the Nakagami distributions for different scintillations conditions. The work presented in this paper is applicable to the analysis and design of optical wireless communication links through the ionosphere and deep space plasma.

Sensitivity enhancement in magnetic sensor using CoFeB/Y3Fe5O12 resonator

Magnonics, an emerging research field that uses the quanta of spin waves as data carriers, has a potential to dominate the post-CMOS era owing to its intrinsic property of ultra-low power operation. Spin waves can be manipulated by a wide range of parameters; thus, they are suitable for sensing applications in a wide range of physical fields. In this study, we designed a highly sensitive, simple structure, and ultra-low power magnetic sensor using a simple CoFeB/Y3Fe5O12 bilayer structure. We demonstrated that the CoFeB/Y3Fe5O12 bilayer structure can create a sharp rejection band in its spin-wave transmission spectra. The lowest point of this strong rejection band allows the detection of a small frequency shift owing to the external magnetic field variation. Experimental observations revealed that such a bilayer magnetic sensor exhibits 20 MHz frequency shifts upon the application of an external magnetic field of 0.5 mT. Considering the lowest full width half maximum, which is about 2 MHz, a sensitivity of 10–2 mT order can be experimentally achieved. Furthermore, the higher sensitivity in the order of 10–6 T (µT) has been demonstrated using the sharp edge of the rejection band of the CoFeB/Y3Fe5O12 bilayer device. A Y-shaped spin waves interference device with two input arms consisting of CoFeB/Y3Fe5O12 and Y3Fe5O12 has been theoretically investigated. We proposed that such a structure can demonstrate a magnetic sensitivity in the range of {10}^{-9} T (nT) at room temperature. The sensitivity of the sensor can be further enhanced by tuning the width of the CoFeB metal stripe.

Structural, magnetic, and magnetocaloric properties of La0.7Sr0.2Nd0.1Mn1-xNixO3 (x= 0.05, 0.10, and 0.15): B-site doping

In this study, La0.7Sr0.2Nd0.1Mn1-xNixO3 (x = 0.05, 0.10, 0.15) systems were synthesized following the sol-gel (SG) approach and their structural, magnetic, and magnetocaloric characteristics were determined. The X-ray Diffraction (XRD) patterns revealed that all samples were in the R-3c space group. Magnetic studies revealed that an increase in the Ni2+ dopant resulted in a ferromagnetic (FM) to paramagnetic (PM) transition near the Curie temperature (Tc), when Tc decreased from 280 K to 220 K. The maximum change in magnetic entropy (−ΔSMMax) gradually decreased while the relative cooling power (RCP) gradually increased. The −ΔSMMax and RCP values for La0.7Sr0.2Nd0.1Mn0.95Ni0.05O3 were 4.28 J/(kg·K) and 267.67 (J/kg), respectively at 280 K when the external magnetic field variation was 5 T. This material can potentially be one of the candidates for developing the magnetic refrigeration technology.

Simulation of Variable Magnetic Field Effect on Natural Convection Heat Transfer of Fe3O4/Graphite Slurry based on Experimental Properties of Slurries

Natural convective heat transfer of Fe3O4/graphite slurry in a square cavity is numerically examined. The slurry is assumed to be a non-Newtonian ferrofluid under a variable external magnetic field. The left and right walls of the cavity are assumed to be at a relatively low temperature (Tc), while the horizontal walls are thermally insulated. A heat source with a variable temperature distribution is located at the bottom of the enclosure. The non-Newtonian behavior of the graphite slurry (a mixture of ethylene glycol and graphite powder) has been modelled using experimental results. The control volume method and the SIMPLE algorithm were used to discretize and solve the governing equations considering the Ferro-hydrodynamics (FHD), the Magnetohydrodynamics (MHD) and the non-Newtonian fluid behavior. The heat transfer and fluid flow properties are determined for different locations of the magnetic field source, and different values of the magnetic number (Kelvin force), and the Hartmann number (Lorentz force). The results show that when the magnetic field source is located below the enclosure and near the heat source, the vortices are strengthened resulting in an increased heat transfer. The heat transfer rate is affected by FHD and MHD. When the magnetic field source is located at the corner points, the heat transfer rate is not significantly affected by the magnetic and Hartmann numbers. However, once the magnetic field source is located near the central point of the lower wall of the enclosure, the heat transfer rate is influenced by the increase of the magnetic number.

Effect of Zeolite Addition on Partial Discharge and Dielectric Behavior of Thermally Aged Synthetic Ester Fluid Under External Magnetic Field

In recent times, ester based liquids have met high standards and are being considered as potential alternatives over mineral oil transformer insulation. This paper investigates the effect of adding micro-porous zeolite to the thermally aged synthetic ester oil (SEO) to evaluate its electrical performance under the influence of external local magnetic field variation from 0 mT to 165 mT. It is observed that the Corona Inception Voltage (CIV) and Particle Levitation Voltage (PLV) have a declining tendency with ageing, in the presence of magnetic field. Under the influence of magnetic flux density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\simeq 160$ </tex-math></inline-formula> mT), the detected UHF signal was dominant at low frequencies (400 MHz - 900 MHz). The UHF voltage signals peak-to-peak magnitude demonstrates that the discharge magnitude increases with increased ageing duration. Further, it was observed that the addition of zeolite in the synthetic ester liquid tends to improve the electrical performance of the aged oil. The fluorescence spectroscopic analysis shows a shift of the fluorescence maxima together with increased intensity in samples with zeolite as compared to the samples without zeolite addition, which shows a relatively lower concentration of the polar contamination. The frequency dielectric spectroscopy also confirms that synthetic ester specimens showed improved dielectric properties after the zeolite treatment.

A new one-dimensional photonic crystal magnetic sensor based on magnetic fluid film with excellent sensing ability and figure of merit

A magnetic sensor based on a one-dimensional (1D) photonic crystal was proposed. The transmission characteristics of the 1D photonic crystal magnetic sensor were analyzed using the theory of rigorous coupled wave analysis (RCWA). The variation pattern of magnetic fluid films refractive index with magnetic field and the effect of structural parameters on sensitivity and figure of merit (FOM) were investigated. Based on the wavelength interrogation method, the resonance wavelength is red-shifted with the change of the magnetic field for certain structural parameters. The results show that the structure has a highly linear response within the external magnetic field variation range from 30 Oe to 90 Oe, and its sensitivity and FOM can reach 0.817 nm/Oe and 17.439 Oe−1. Due to the advantages of 1D photonic crystal structure has harp peak, highly linear response, and low transmission loss. The structure has a large potential for applications in complex environments and real-time monitoring.

Terahertz vortex beam propagation through a magnetized plasma-ferrite structure

Interaction of vortex beams with materials has proven to be a key for controlling and exploiting theirs properties. In this paper, we propose an adjustable stratified structure constructed from plasma and ferrite layers, which greatly manipulates the intensity and phase distributions of incoming terahertz vortex beam (TVB), and demonstrates a considerable amount of Faraday rotation. To obtain the output beam profiles, first using angular spectral expansion technique the incoming TVB is decomposed into a superposition of plane waves, then employing 4×4 matrix formalism total reflection and transmission coefficients are extracted. Numerical analysis reveals that how the variations of external static magnetic field, incident angle, and radial and angular indices of the TVB affect the features of reflected and transmitted beams. It is expected that this investigation will shed new light on the interaction of TVB with anisotropic magnetic materials, and open new possibilities for wavefront engineering and material characterization.