External Magnetic Field Research Articles

Effect of the magnetic field on the conductance and spin polarization in phosphorene superlattice

The spin-dependent conductance and spin polarization are investigated theoretically in a phosphorene superlattice in the presence of external magnetic field and Rashba interaction. It is demonstrate that, the spin-dependent conductance with and without spin-flip as well as spin polarization can be effectively controlled by changing the magnetic field strength and the number of the superlattice barriers. For small magnetic field strength, the conductance for with and without spin-flip shows an oscillating behavior as increasing the strength of the Rashba interaction, and by increasing the number of barriers, the oscillating behavior becomes prominent. Further, when the magnetic field is greater than a limit value, the spin conductance will be zero. The size of the spin-dependent transmission window in the phosphorene superlattice under external magnetic field decreases drastically. The magnitude, sign and behavior of the spin polarization can be tuned by the amount of the external magnetic field.

Mössbauer and magnetization measurements of multicomponent iron garnets

Four Gd-containing iron garnets were investigated using Mössbauer spectroscopy and Vibrating Sample Magnetometry over a wide temperature range, from 4K to ∼600K. The magnetic ordering temperature and hyperfine parameters determined on the basis of Mössbauer spectra for all samples were found to be surprisingly similar, differences were only noted for the average magnetic moments, which turned out to be strongly correlated with the magnetic moments of rare earth elements present in the structure. Further differences between the systems were also highlighted in measurements in the external 9T magnetic field, especially around the compensation temperature. Changes in the nature of the Mössbauer spectra were interpreted based on the crystal field approximation confirming the correctness of the interpretation of the temperature dependence of magnetization for these samples.

Exploring the complex interplay of factors in convective heat transfer: a comprehensive parametric analysis in three-dimensional permeable cavities

ABSTRACT This examination aimed to mathematically investigate the blended convective intensity movement inside a three-layered nook that consolidates a spinning roundabout chamber and an undulating permeable pit. Using the limited component technique (FEM), mathematical reproductions were executed across different boundaries, enveloping the Darcy number going from 10 − 5 to 10 − 2 Hartmann number (going from 0 to 100, the angular velocity between − 4000 and 4000, and the number of undulations in the permeable pit. The results, addressed through stream capability, isotherms, and isentropic forms, clarify the effect of these boundaries on movement, heat transport, and entropy age. The ends suggest that for an ideal upgrade of intensity move rates in a three-layered undulating permeable cavity with a pivoting chamber and exposed to an attractive field, explicit circumstances are suggested, a Darcy number more prominent than or equivalent to 10 − 2 , a Hartmann number of 0, undulation of the permeable pit (N = 3), and angular velocity surpassing 2000 in the stream heading. The study investigates convective heat transfer in a rotating cylindrical chamber, analyzing parameters like Darcy number, Hartmann number, and rotation speed for optimizing heat transfer systems in complex porous cavities. The optimal heat transfer occurs when the aspect ratio is fixed at 0.3 and porous media occupies 90% of the channel. A 150% enhancement in the Nusselt number can be observed when the cylinder’s rotational speed increases. The study also found that increasing angular velocity and Darcy number positively affects the Nusselt number. The research aims to understand the interplay of factors affecting convective heat transfer and fluid dynamics and offer practical implications for optimizing heat transfer systems. The novelty of this study lies in its thorough examination of convective heat transfer in a rotating cylinder-shaped porous cavity, focusing on factors like Darcy number, Hartmann number, rotation speed, and pit geometry. It provides insights for optimizing heat transfer efficiency in complex cavities and explores the impact of external magnetic fields and fluid dynamics. The study investigates the influence of parameters like Hartmann number, angular speed, and Darcy number on thermal and flow characteristics in a porous cavity filled with Fe3O4/MWCNT-water nanofluid, highlighting their importance for optimizing heat transfer efficiency.

An optically pumped magnetic gradiometer for the detection of human biomagnetism

We realise an intrinsic optically pumped magnetic gradiometer based on non-linear magneto-optical rotation. We show that our sensor can reach a gradiometric sensitivity of 18 fT cm−1Hz−1 and can reject common mode homogeneous magnetic field noise with up to 30 dB attenuation. We demonstrate that our magnetic field gradiometer is sufficiently sensitive and resilient to be employed in biomagnetic applications. In particular, we are able to record the auditory evoked response of the human brain, and to perform real-time magnetocardiography in the presence of external magnetic field disturbances. Our gradiometer provides complementary capabilities in human biomagnetic sensing to optically pumped magnetometers, and opens new avenues in the detection of human biomagnetism.

Ferromagnetic Order in 2D Layers of Transition Metal Dichlorides.

Magnetism in two dimensions is traditionally considered an exotic phase mediated by spin fluctuations, but far from collinearly ordered in the ground state. Recently, 2D magnetic states have been discovered in layered van der Waals compounds. Their robust and tunable magnetic state by material composition, combined with reduced dimensionality, foresee a strong potential as a key element in magnetic devices. Here, a class of 2D magnets based on metallic chlorides is presented. The magnetic order survives on top of a metallic substrate, even down to the monolayer limit, and can be switched from perpendicular to in-plane by substituting the metal ion from iron to nickel. Using functionalized STM tips as magnetic sensors, local exchange fields are identified, even in the absence of an external magnetic field. Since the compounds are processable by molecular beam epitaxy techniques, they provide a platform with large potential for incorporation into current devicetechnologies.

Magnetic domain wall dynamics studied by in-situ Lorentz microscopy with aid of custom-made Hall-effect sensor holder

We built a custom-made holder with a Hall-effect sensor to measure the single point magnetic flux density inside a transmission electron microscope (TEM, JEM-F200, JEOL). The measurement point is at the same place as the sample inside the TEM. We utilized information collected with the Hall-effect sensor holder to study magnetic domain wall (DW) dynamics by in-situ Lorentz microscopy. We generated an external magnetic field to the sample using the objective lens (OL) of the TEM. Based on our measurements with the Hall-effect sensor holder, the OL has nearly linear response, and when it is switched off, the strength of the magnetic field in the sample region is very close to 0 mT.A ferritic-pearlitic sample studied has globular and lamellar cementite (Fe3C) carbides in the ferrite matrix. Based on the in-situ Lorentz microscopy experiments, DWs in the ferritic matrix perpendicular to the lamellar carbides start to move first at ∼10 mT. At 160 mT, DWs inside the globular carbide start to disappear, and the saturation occurs at ∼210 mT. At 288 mT, the DWs parallel to the lamellar carbides still exist. Thus, these lamellar carbides are very strong pinning sites for DWs. We also run dynamical micromagnetic simulations to reproduce the DW disappearance in the globular carbide. As in the in-situ experiments, the DWs stay stable until the external field reaches the magnitude of 160 mT, and the DWs disappear before the field is 214 mT. In general, the micromagnetic simulations supported very well the interpretation of the experimental findings.

Improving the frictional properties of the tool/chip interface of micro-textured ceramics tools by using electromagnetic-assisted nanofluids

During the machining of stainless steel by ceramics tools, the tool/chip interface is difficult to be effectively cooled and lubricated due to the poor thermal conductivity of ceramic and stainless steel materials, resulting in the high cutting temperature and severe tool wear. To enhance the penetration of nanofluid into the tool/chip interface, a novel approach of magnetic field-assisted electroosmotic was proposed. The external magnetic field was introduced during the cutting process, and the self-excited electric field generated by intense tool/workpiece interface friction was considered. The effect of electromagnetic field-assisted Fe3O4 nanofluid lubrication on the cutting performance of micro-textured tool was investigated. The results showed that Fe3O4 nanofluid (NF) can be effectively migrated to the tool/chip interface driven by the electroosmotic force, Lorentz force and pressure to alleviate the tool wear. In particular, with increasing of electromagnetic field strength, the cutting performance was significantly improved. In addition, the mechanism of NF permeation at the micro-textured tool/chip interface under the electromagnetic field was revealed by combining the finite element simulation. This work provides a new method for efficient cooling and lubrication of the tool/chip interface during the machining of difficult-to-cut materials, and the drive theory of cutting fluid penetration is also enriched.

Synthesis, properties and applications of new hybrid material based on native/magnetically modified sepiolite and chitosans

The study introduces novel hybrid materials containing native and magnetite-containing sepiolite (Sep, SepM respectively) and chitosans (Ch) of different molecular weights. The main objective of this work was to determine the properties of these materials, including the different types of stability (colloidal, gravitational and thermal) in systems containing sepiolite, in order to obtain effective, stable and easily producible hybrid materials with great potential for water and wastewater treatment. The following measurements and methods were performed to characterize the investigated system: low-temperature nitrogen adsorption–desorption, zeta potential analysis, UV–Vis, FT-IR, XRD, XRF, SEM-EDS, TGA, DSC and DTG. It was found that the complexes with high molecular weight chitosan exhibited the best stability of the systems. The same tendency was observed for the concentration dependence: the higher the chitosan concentration, the better the stabilization of the composites. Overall, this study shows that chitosan effectively improves the colloidal and gravitational stability of the composites. Due to its unique structure, the synthesized magnetic hybrid material has shown great advantages in the adsorptive removal of textile dyes such as anionic acid red 88 (AR88) and cationic methylene blue (MB) which can be easily removed from the dye solutions after its use using an external magnetic field.

Field-Free Spin-Orbit Torque Magnetization Switching in a Perpendicularly Magnetized Semiconductor (Ga,Mn)As Single Layer.

Current-induced spin-orbit torque (SOT) in a perpendicularly magnetized single layer has a strong potential to switch the magnetization using an extremely low current density, which is generally 2-3 orders of magnitude smaller than that required for conventional metal bilayer systems. However, an in-plane external magnetic field has to be applied to break the symmetry and achieve deterministic switching. To further enhance the high-density integration and accelerate the practical application of highly efficient SOT magnetic random-access memory (SOT-MRAM) devices, field-free SOT magnetization switching in a ferromagnetic single layer is strongly needed. In a spin-orbit ferromagnet (a ferromagnet with strong spin-orbit interaction) with crystal inversion asymmetry and a multi-domain structure, the internal Dzyaloshinskii-Moriya effective fields are considered to induce field-free switching. Here, combined with strong spin-orbit coupling and a tilted anisotropy axis induced by a nonuniform Mn distribution and a possible magnetocrystalline anisotropy resulting from a slight substrate tilting, we successfully achieve magnetization switching in a spin-orbit ferromagnet (Ga,Mn)As single layer by utilizing SOT without applying any external magnetic field. Our findings help to deeply elucidate the SOT switching mechanism and can advance the development of a highly efficient MRAM with better scalability.

Synthesis of reusable graphene oxide based nickel-iron superparamagnetic nanoadsorbent from electronic waste for the removal of doxycycline in aqueous media

Graphene oxide-based nickel-iron superparamagnetic nanoadsorbent (GO/Ni-Fe) was synthesized from electronic waste to effectively remove doxycycline (DXC) in aqueous media. The GO/Ni-Fe nanoadsorbent has been characterized using a number of instrumental techniques, including X-ray diffractometer, Zeta potential, Fourier transform infrared spectroscopy, elemental analyzer, vibrating sample magnetometer, transmission electron microscopy, energy dispersive x-ray, and X-ray photoelectron spectroscopy. These techniques showed that nickel-iron (Ni-Fe) nanoparticles with an average size of 4.26 nm were successfully fabricated on GO surfaces. The batch experiments were conducted under different conditions, including contact time, adsorption dosage, pH, concentration, and temperature, to determine the optimal conditions of the adsorption process. The maximum adsorption (90% removal) was established within 20 min, while the adsorbent dose was only 0.1 g/L at pH 5. The adsorption process was best fitted with the pseudo-second-order model, which suggests the interaction of doxycycline with the GO/Ni-Fe nanoadsorbent is mainly controlled by the chemisorption process. This may be due to hydrogen bonding as well as electrostatic interaction and π-π interaction between adsorbates and adsorbents. The isotherm data of the adsorption process was best fitted with Langmuir isotherm model with a maximum adsorption capacity of 13.02 mg g−1 at 25 °C, indicating that the adsorption is a monolayer adsorption to heterogeneous surfaces with electrostatic interaction. The superparamagnetic properties of GO/Ni-Fe nanoadsorbent can be easily separated by external magnetic field and regenerated with methanol washing. The findings unambiguously demonstrated that magnetically separable GO/Ni-Fe nanoadsorbent could be a good choice to remove DXC from wastewater sources.

A magnetic/force coupling assisted lithium-oxygen battery based on magnetostriction and piezoelectric catalysis of CoFe2O4/BiFeO3 cathode

The high energy density of Li−O2 batteries surpasses all existing batteries, and it holds the potential to emerge as the most outstanding solution for energy storage in the future. However, the insulated, insoluble discharge product (Li2O2) has impeded the practical applications. Conventional catalyst design based on electronic structure and interfacial charge transfer descriptors are incapable of overcoming these limitations of Li2O2. Herein, a magnetic/force coupling assisted Li−O2 battery based on magnetostrictive and piezoelectric catalysis with CoFe2O4/BiFeO3 core-shell structure cathode was established for the first time. An external magnetic field is introduced to produce a magnetostrictive stress on CoFe2O4, contributing to the piezoelectric electron hole transport by the generated piezoelectric potential energy with a built-in electric field based on the piezoelectric catalytic mechanism, and thus promoting the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics, and reducing the overpotential during charge/discharge. The magnetic/force coupling assisted Li−O2 battery equipped with the unique CoFe2O4/BiFeO3 cathode deliver an ultra-low charging platform of 3.49 V and an ultra-high discharge platform of 2.83 V. This unique magnetic/force assisted strategy provides an important insight into solving the high overpotential in metal-air battery systems.

Biexcitons and quadrons in self-assembled quantum dots

We theoretically study biexcitons and quadrons in quantum dots with parabolic confinement and give a complete comparison between the two excitations. The calculation of quadron and biexciton binding energies as functions of electron-to-hole confinement potentials and mass ratios, using the unrestricted Hartree–Fock method, shows the essential differences between biexcitons and quadrons. The crossover between the negative and positive binding energies is indicated. The effect of an external magnetic field on the quadron and biexciton binding energies has also been investigated. In addition, the crossover between anti-binding and binding of both excited quadron and biexciton states in a certain range of the electron-to-hole oscillator length ratios has been found.

True and False Chirality in Chiral Magnetic Nanoparticles.

Determining the true or false chirality of a system is essential for the design of advanced chiral materials and for improving their applications. Typically, a magnetic field would cause false optical activity in the chiral material system, thus confusing the true chirality's influence. Here, we provide a simple way to uncover the true and false chirality in chiral ferrimagnetic nanoparticles (FNPs) by using the gel as a rigid frame. The remnant local magnetic field of the FNP gel can be easily adjusted by an external magnetic field or by controlling the concentration of the FNPs. Moreover, the potential application of the FNP gel is detected by induced magnetic circularly polarized luminescence. This work provides deep insight into the true and false chirality in magnetic nanosystems and offers a strategy to construct new optic elements with an adjustable local magnetic field.

Massive Dirac particles based on gapped graphene with Rosen-Morse potential in a uniform magnetic field

Abstract In this paper, we explore the gapped graphene structure in the two-dimensional plane in the presence of the Rosen-Morse potential and the external uniform magnetic field. In order to describe the corresponding structure, we consider the propagation of electrons in graphene as relativistic fermion quasi-particles, and analyze it by the wave functions of two-component spinors with pseudo-spin symmetry using the Dirac equation. Next, to solve and analyze the Dirac equation, we obtain the eigenvalues and eigenvectors using the Legendre differential equation. After that, we obtain the bounded states of energy depending on the coefficients of Rosen-Morse and magnetic potentials in terms of quantum numbers of principal n and spin-orbit k. Then, the values of the energy spectrum for the ground state and the first excited state are calculated, and the wave functions and the corresponding probabilities are plotted in terms of coordinates r. In what follows, we explore the band structure of gapped graphene by the modified dispersion relation and write it in terms of the two-dimensional wave vectors K x and K y . Finally, the energy bands are plotted in terms of the wave vectors K x and K y with and without the magnetic term.

Magnetic behaviors of diatomic molecules with mixed spin-1 and spin-1/2 on the Bethe lattice

It is considered that each Bethe lattice (BL) site is inhabited by a diatomic molecule made up of either two spin-1/2 or two spin-1 atoms, respectively. Then, each diatomic molecule is thought to interact with others via its atoms in terms of numerous bilinear interaction parameters, such as the interaction of atoms within each molecule and the interaction of atoms between molecules. The thermal fluctuations of magnetizations for the diatomic molecule are examined by incorporating a crystal field for the spin-1 atoms and mapping their magnetic phase diagrams on the BL with coordination number q=3 using exact recursion relations (ERR). The effects of the external magnetic field are also taken into account while analyzing the thermal fluctuations in magnetizations. For various antiferromagnetic (AFM) and ferromagnetic (FM) interaction setups, the model always presents second- and first-order phase lines merging at a tricritical point (TCP). The acquired results are compared to those of a BL, in which each site is associated with only one atom.

Examining the role of magnetic fields in plasma behavior and surface evolution of a Mg alloy with varied irradiances in a femtosecond laser treatment

This paper reports the effect of a magnetic field on plasma parameters and surface structuring of the Mg alloy after laser irradiation. Femtosecond pulses of a Ti:sapphire laser system (800 nm, 35 fs, 1 KHz) are employed as the source of irradiation at various irradiances ranging from 0.011PW/cm2 to 0.117PW/cm2 to generate ablated Mg-alloy plasma. A transvers magnetic field (TMF) of strength 1.1 Tesla is employed to confine laser generated Mg plasma. All the measurements are performed with and without TMF. The two plasma parameters, i.e., excitation temperature (Texc) and electron number density (n e ) of Mg plasma, have been evaluated by laser-induced breakdown spectroscopy (LIBS) analysis. It is observed that the values of Texc and n e of laser produced plasma (LPP) of the Mg alloy are higher in the presence of a magnetic field as compared to the field free case. Both show initially an increasing trend with increasing laser irradiance and after attaining their respective maxima a decreasing trend is observed with the further increase of irradiance. The magnetic confinement validity is confirmed by analytically evaluating thermal beta (β t ), directional beta (β d ), confinement radius (R b ), and diffusion time (t d ) for LPP of the Mg alloy. To correlate the LPP parameters of the Mg alloy with surface modifications a field emission scanning electron microscope (FE-SEM) analysis is performed. It was revealed that structures like laser-induced periodic surface structures (LIPSSs), agglomerates, islands, large sized bumps, along with channels and multiple ablative layers are observed. Distinct and well-defined surface structuring is observed in the presence of TMF as compared to the field free case. It is concluded that by applying an external magnetic field during laser irradiation, controlled material surface structuring is possible for fabrication of nanogratings and field emitters where spatial uniformity is critically important.

Quantum Size-Driven Spectral Variations in Pillar[n]arene Systems: A Density Functional Theory and Wave Function Assessment.

This study explores the quantum size effects on the optical properties of pillar[n]arene (n = 5, 6, 7, 8) utilizing density functional theory (DFT) and wave function analysis. The mechanisms of electron transitions in one-photon absorption (OPA) and two-photon absorption (TPA) spectra are investigated, alongside the calculation of electron circular dichroism (ECD) for these systems. Transition Density Matrix (TDM) and electron-hole pair density maps are employed to study the electron excitation characteristics, unveiling a notable size dependency. Analysis of the transition electric dipole moment (TEDM) and the transition magnetic dipole moment (TMDM) reveals the electromagnetic interaction mechanism within pillar[n]arene. Raman spectra computations further elucidate vibrational modes, while interactions with external environments are studied using electrostatic potential (ESP) analysis, and electron delocalization is assessed under an external magnetic field, providing insights into the magnetically induced current phenomena within these supramolecular structures. The thermal stability of pillar[n]arene was investigated by ab initio molecular dynamics (AIMD).

Effect of magnetized water irrigation on Cd subcellular allocation and chemical forms in leaves of Festuca arundinacea during phytoremediation

The application of an external magnetic field has been shown to improve the Cd phytoremediation efficiency of F. arundinacea by leaf harvesting. However, the influencing mechanisms of the promoting effect have not yet been revealed. This study evaluated variations in the Cd subcellular allocation and fractions in various F. arundinacea leaves, with or without magnetized water irrigation. Over 50 % of the metal were sequestered within the cell wall in all tissues under all treatments, indicating that cell wall binding was a critical detoxification pathway for Cd. After magnetized water treatment, the metal stored in the cytoplasm of roots raised from 33.1 % to 45.3 %, and the quantity of soluble Cd in plant roots enhanced from 53.4 % to 59.0 %. The findings suggested that magnetized water mobilized Cd in the roots, and thus drove it into the leaves. In addition, the proportion of Cd in the organelles, and the concentration of ethanol-extracted Cd in emerging leaves, decreased by 13.0 % and 47.1 %, respectively, after magnetized water treatment. These results explained why an external field improved the phytoextraction effect of the plant through leaf harvesting.

Magnetic Magnetite-Graphene Oxide (Fe3O4-GO) Nanocomposites for Removal of Dyes from Aqueous Solution

AbstractMagnetic magnetite-graphene oxide (Fe3O4-GO) was synthesized using an in-situ precipitation technique and applied in the adsorption of cationic rhodamine B (RhB) and anionic methyl orange (MO) dyes from aqueous solution. The nanocomposite was characterized by different techniques including FTIR, XRD, Raman, XPS, PPMS, BET, SEM and TEM techniques. Batch adsorption studies were conducted to investigate the effect of solution pH, initial metal ion concentration, adsorbent dosage and contact time. The synthesized Fe3O4-GO exhibited characteristic magnetic properties (saturation magnetization of 34 emu/g) and it separated from aqueous solution with ease through the application of an external magnetic field. The adsorption equilibrium time on the adsorption of RhB and MO onto Fe3O4-GO showed best removal of 99.12% for RhB after 60 min, while MO was removed efficiently after 120 min with a removal efficiency of 97.60%. The adsorption of the azo dyes followed the pseudo-second-order kinetics model with high correlation coefficients (0.99995) for RhB and (0.99925) for MO. Maximum removal of the dye pollutants by occurred at pH 8 for RhB and pH 4 for MO, while the optimal adsorbent dosage was 30 mg. The results showed that adsorption equilibrium data were fitted to Langmuir isotherm model and maximum monolayer adsorption capacities for RhB and MO at 70.64 and 15.94 mgg−1, respectively. The magnetic adsorbents were reused for a maximum of 7 cycles and showed reasonable stability and reproducibility. Furthermore, the results showed that Fe3O4-GO nanocomposite can be used as an effective material in the removal of dyes from wastewater.

Dual-polarization small-angle strong nonreciprocal thermal radiator with Weyl semimetal

The development of dual-polarization irreversible radiators that can operate without external magnetic field is an arduous task. To avoid the need of strong magnetic field, a dual-polarization nonreciprocal thermal radiator with the introduction of Weyl semimetal is demonstrated. It consists of cross-shaped silicon nanopores, Weyl semimetal, and Ag reflective layer. The simulation results show that the proposed radiator offers both TE- and TM-polarized strong irreversible radiation with an incident angle of 1.6°. The TE-polarized absorptivity and TM-polarized emissivity are 98.8% and 97.6%, respectively. The dual-polarization nonreciprocity exceeds 80%. The physical principle is explained by the electric field energy distribution and impedance matching theory. The demonstrated scheme and radiator have potential application in dual-polarization multi-band irreversible radiation and thermal management.