Assistance Of Magnetic Field Research Articles

Spin Reflection-Induced Field-Free Magnetization Switching in Perpendicularly Magnetized MgO/Pt/Co Heterostructures.

Field-free magnetization switching is critical towards practical, integrated spin-orbit torque (SOT)-driven magnetic random-access memory with perpendicular magnetic anisotropy. Our work proposes a technique to modulate the spin reflection and spin density of states within a heavy-metal Pt through interfacing with a dielectric MgO layer. We demonstrate tunability of the effective out-of-plane spin torque acting on the ferromagnetic Co layer, enabling current-induced SOT magnetization switching without the assistance of an external magnetic field. The influence of the MgO layer thickness on effective SOT efficiency shows saturation at 4 nm, while up to 80% of field-free magnetization switching ratio is achieved with the MgO between 5 and 8 nm. We analyze and attribute the complex interaction to spin reflection at the dielectric/heavy metal interface and spin scattering within the dielectric medium due to interfacial electric fields. Further, through substituting the dielectric with Ti or Pt, we confirm that the MgO layer is indeed responsible for the observed field-free magnetization switching mechanism.

Tuning isolated zero-field skyrmions and spin spirals at room-temperature in synthetic ferrimagnetic multilayers

We demonstrate the observation of spin spirals and individual skyrmions in synthetic Pt/CoGd/Pt ferrimagnetic multilayers at room-temperature without the assistance of an external magnetic field. The magnetic coupling between the magnetic moments of Co and Gd, was investigated across various CoGd thicknesses by element specific X-ray magnetic circular dichroism (XMCD) performed around the Co L2,3 and Gd M4,5 edges. It shows an uncompensated ferrimagnetic orientation between the Co and Gd atoms preserved at ambient conditions, even for sub-nanometer thick layers. In addition, with the tunable enhanced perpendicular magnetic anisotropy Ku and remnant magnetization MR found for thinner CoGd ≤ (0.9 nm) isolated zero-field skyrmions were imaged by magnetic force microscopy (MFM) as the magnetic ground state, replacing the spin spirals observed for thicker CoGd layers ≥ (1.2 nm). Such stable skyrmions in perpendicularly magnetized materials with antiparallel exchange-coupling are potential candidates for energy-efficient data storage and processing in future antiferromagnetic-based devices.

Effect of steady magnetic field on microstructure and properties of laser cladding Ni-based alloy coating

In this paper, Ni-based alloy coating was prepared on pure iron substrate by steady magnetic field assisted laser cladding technology. The influence mechanism of steady magnetic field on the Ni-based coating was investigated by analyzing the macro-morphology, phase composition, microstructure, element composition and properties of the coatings, respectively. The results reveal that external magnetic field can restrain the surface fluctuation of the coatings. It has no effect on the phase composition of the coatings. Compared with the coating prepared without magnetic field assistance, the grains of the coatings prepared under the magnetic induction intensities of 0.1 T, 0.15 T and 0.2 T are all refined. The solid solubility of the γ-Ni matrix is also increased. Hard phases CrB in the microstructures appear clustered aggregation and preferential orientation with the increase of the magnetic induction intensity. The application of steady magnetic field is beneficial to reduce the number of cracks on the surface and improve the microhardness of the coatings. The coating exhibits the best comprehensive property under the magnetic induction intensity of 0.2 T. Under the action of steady magnetic field, the electromagnetic braking effect and the thermoelectric magnetic fluid effect can both influence the laser cladding process. The surface morphology of the coating is mainly affected by the electromagnetic braking effect. The solidification microstructure is mainly controlled by the thermoelectric magnetic fluid effect.

Theoretical and experimental investigations of magnetic field assisted ultra-precision machining of titanium alloys

Although titanium (Ti) alloys possess unique properties that allow them to compete with many other materials in advanced industries such as aerospace, marine and biomedical, they have poor machining performances. The primary objective of this study is to investigate the distribution of magnetic field intensity at the cutting environment in single-point diamond turning (SPDT) of Ti–6Al–4 V alloy and its influence on the machining performances, with the goal of achieving the desired machining conditions of magnetic field assisted ultra-precision machining, especially magnetic field intensity and the corresponding machining parameters, and to enhance the machinability of Ti–6Al–4 V alloy. In this study, magnetic field-assisted machining (MFAM) system was designed and coupled with ultra-precision machining (UPM) using single-point diamond turning for increasing the machinability and improving the surface quality of Ti6Al4V alloy machined parts. The finite element method (FEM) was developed to demonstrate the influences of the generated magnetic field on the machining processes. The Experimental results showed the capability of magnetic field assistance to enhance the machining performance of Ti–6Al–4 V alloy. These findings provided strong evidence that a magnetic field has the ability to extend cutting tool life, additionally, MFAM achieved the lowest value of surface roughness, representing a 33 percent improvement in surface roughness. This research contributes to the support of the optimum MFAM by FEM and the achievement of high-quality machined Ti alloys in UPM for similar research works, as demonstrated by the experimental results.

Thickness-Driven Quantum Anomalous Hall Phase Transition in Magnetic Topological Insulator Thin Films.

The quantized version of the anomalous Hall effect realized in magnetic topological insulators (MTIs) has great potential for the development of topological quantum physics and low-power electronic/spintronic applications. Here we report the thickness-tailored quantum anomalous Hall (QAH) effect in Cr-doped (Bi,Sb)2Te3 thin films by tuning the system across the two-dimensional (2D) limit. In addition to the Chern number-related QAH phase transition, we also demonstrate that the induced hybridization gap plays an indispensable role in determining the ground magnetic state of the MTIs; namely, the spontaneous magnetization owing to considerable Van Vleck spin susceptibility guarantees the zero-field QAH state with unitary scaling law in thick samples, while the quantization of the Hall conductance can only be achieved with the assistance of external magnetic fields in ultrathin films. The modulation of topology and magnetism through structural engineering may provide useful guidance for the pursuit of other QAH-based phase diagrams and functionalities.

Magnetic induced asymmetric membrane: Effect of magnetic pattern to phenol removal by adsorption

Randomized particle distribution in a mixed matrix membrane would reduce the effectiveness of particle immobilized in its matrix. This study aims to distribute the particle near the membrane surface with magnetic field assistance. Specifically, investigating the influence of varied magnetic patterns (rod, chain, and circular) on zinc ferrite distribution in the membrane on the phenol adsorption with the standing time was fixed at 30 s with 12 wt% zinc ferrite. The findings revealed that the magnetic induce membrane possesses the highest phenol adsorption, especially by membrane fabricated by magnets in a circular pattern (MB). MB membrane displayed phenol adsorption capacity of 415 mg/g with water permeation of 30.4 L/m2.h. The high phenol adsorption was contributed to high zinc ferrite particle migrated towards the membrane surface, and EDX analysis revealed 1.23 wt% Fe element in its thin layer region. These findings indicate that the magnets arranged in a circular pattern can effectively migrate and distribute the zinc ferrite across the membrane. Hence, a suitable magnetic pattern was vital when applying magnetic induce casting.

Magnetic-field-free spin–orbit torque-driven magnetization dynamics in CoFeB/β-W-based nanoelements

A full numerical analysis, which takes into account the effects of the spin Hall effect, interfacial Dzyaloshinskii–Moriya interaction, and thermal fluctuations, is carried out in in-plane magnetized CoFeB/MgO/CoFeB/high-resistivity tungsten (β-W) nanoelements. The analysis is focused on the investigation of the underlying mechanisms of magnetic-field-free spin–orbit torque (SOT)-driven magnetization reversal process on subnanosecond time scales. It is found that the magnetization in the free magnetic layer can be electrically toggled between the parallel and antiparallel alignment with respect to the fixed magnetic layer without the assistance of an external magnetic field, in which the out-of-plane canting of the magnetic moments at the element edges plays a significant role in the nucleation and subsequent expansion of the reversed magnetization. Furthermore, the thermally activated magnetization process combined with the SOT effect is found to significantly reduce the effective energy barrier to the magnetization reversal and alter the details of the SOT-driven magnetization process in nanomagnets.

A ratiometric fluorescent probe based on peptide modified MnFe2O4 nanoparticles for matrix metalloproteinase-7 activity detection in vitro and in vivo.

Abnormal expression of matrix metalloproteinases plays an important role in tumor invasion and metastasis. In this report, a peptide modified MnFe2O4 ratiometric fluorescent nanoprobe is developed for noninvasively visualizing the distribution of matrix metalloproteinase-7 (MMP-7) in vitro and in vivo. A fluorescein isothiocyanate (FITC) modified peptide containing the specific motif VPLSLTMG for MMP-7 cleavage was conjugated with MnFe2O4 nanoparticles (NPs) to establish a Förster resonance energy transfer (FRET) system for sensing the protease. The rhodamine B (RhB) modified targeting peptide immobilized on the nanoparticle surface was not only used as an internal reference for forming a ratiometric fluorescence system together with the FITC dye, but also used for enhancing the tumor targeting ability. The tumor accumulation amount of the as-developed ratiometric fluorescent probe (termed MnFe2O4-pep-dyes) can be measured by T2-weighted magnetic resonance (T2-weighted MR) imaging because MnFe2O4 NPs display an excellent T2-weighted MR contrast ability. In the presence of MMP-7, FITC detached from the MnFe2O4 surface resulting in the recovery of FITC fluorescence, while no obvious change of the RhB fluorescence was observed. The recovery ratio of FITC to RhB fluorescence intensity is linearly dependent on the MMP-7 concentration within the range of 0.1 to 15 nM in buffer and 5 × 102 to 1 × 104 cells in cell lysates with a limit of detection of 0.1 nM and 436 cells, respectively. MnFe2O4-pep-dyes was further applied to spatially observe MMP-7 expression in a tumor-bearing mouse by in vivo fluorescence imaging with external magnetic field assistance for demonstrating its practicability.

Pseudospark-Driven High-Current Miniaturized Voltage-Tunable Sheet-Electron-Beam Source

For high-power and compact sub-terahertz (THz) sources, a high-current electron beam is a crucial component. In this article, a miniaturized sheet-electron-beam source has been developed for generation of the high-current-density electron beam. It consists of a hollow cathode with a 3-mm diameter circular aperture, an anode with a 1.25 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.25$ </tex-math></inline-formula> mm rectangular aperture, and an interelectrode three-gap region with optimized dimension. The developed electron beam source has been operated in self-breakdown conditions for applied gap voltage ranging between 10 and 30 kV. The sheet electron beam has been successfully propagated for nearly 45 mm inside the drift space without the assistance of an external magnetic field due to the space charge neutralization effect. It has demonstrated good transmission characteristics with more than 50-A beam current and beam current loss of around 25%.

Bioinspired Superhydrophobic Cilia for Droplets Transportation and Microchemical Reaction

AbstractIn nature, fluid manipulation plays a crucial role in the life of organisms, which has attracted great attentions of research and industry. Here, a functional bionic cilia surface is designed via the simple magnetic field assistance and laser etching technique. Multidirectional droplet transportation occurs on superhydrophobic cilia surface, which has good mechanical, physical, and chemical stability. The as‐prepared surface covered with cilia in the superhydrophobic (WCA of 156 ± 2°) and hydrophobic (WCA of 119 ± 3°) area possess different adhesion state, which can be used for multiple chemical reactions as a microreaction platform. Furthermore, bionic cilia surface can be used as a transport tool in the analysis and detection with average transfer speed of 2.3 cm s−1, which provides new opportunities in the development of small analysis equipment. Importantly, magnetically induced bionic cilia surfaces have broad potential applications in developing smart surfaces, droplet control, lab‐on‐a‐chip, etc.

Bioinspired Virus-like Fe3O4/Au@C Nanovector for Programmable Drug Delivery via Hierarchical Targeting.

Bioinspired strategies have recently emerged as novel approaches for designing a functionalized nanovector with enhanced tumor targeting and therapeutic efficacy. Herein, a virus-like Fe3O4/Au@C nanovector is described for programmable drug delivery via hierarchical targeting. Specifically, the virus-like Fe3O4/Au@C nanovector is synthesized via a simple hydrothermal process, and then the spiky surface of which is camouflaged via doxorubicin (DOX)-conjugated polyethylene glycol (PEG), constructing an innovative virus-like core/spherical shell biomimetic nanomedicine (Fe3O4/Au@C-DOX-PEG), which is conducive to improve bioavailability and reduce adverse effects. After systemic administration, the as-prepared nanomedicine is capable of facilitating effective tumor accumulation and deep tumor penetration with the assistance of an external magnetic field and endogenous pH stimuli. Simultaneously, in response to the acidic tumor microenvironment, Fe3O4/Au@C-DOX nanocomposites are released and exhibit excellent performance in cellular internalization through a virus-mimetic rough surface. Furthermore, the in vivo experiments identify that the unique nanomedicine is bestowed with an effective targeting tumor, prominent antitumor efficacy, and reduced systemic toxicity. Such a bioinspired hierarchical targeting nanoplatform holds promising potential for enhanced chemotherapeutic intracellular delivery and tumor theranostics.

WITHDRAWN: Significantly enhancing fracture toughness of epoxy composite with promising γ-FeOOH@Fe2O3 hybrid nanoparticles by magnetic field assistance

Abstract The toughening of epoxy resin (EP) and the interlaminar toughening of carbon fiber reinforced composite (CF/EP) laminates have been widely concerned. In this work, the needle-like γ-FeOOH nanoparticles were prepared by liquid phase deposition-air oxidation method, and then were calcined under different conditions to obtain γ-FeOOH and γ-Fe2O3 hybrid nanoparticles (γ-FeOOH@Fe2O3). Effect of calcination condition of γ-FeOOH@Fe2O3 and magnetic field assistance on fracture toughness (KIC) of EP was systematically investigated. Then the selected γ-FeOOH@Fe2O3 with the best toughening effect were used to improve the mode I interlaminar fracture toughness (GIC) of CF/EP laminate. The resulting γ-FeOOH@Fe2O3 have a length of around 1 ​μm, a diameter of around 100 ​nm and the Ms of 8.99–45.96 emu/g. After calcinated at 250 ​°C for 1 ​h, the γ-FeOOH@Fe2O3 containing 24 ​wt% FeOOH and 76 ​wt% Fe2O3 achieved the best toughening effect. Under a magnetic field of 0.09 ​T, the KIC of the γ-FeOOH@Fe2O3/EP composite (2.45 ​MPa ​m1/2) is 81.7% and 66.7% higher than that of neat epoxy and the composite without magnetic field induction, respectively. Furthermore, the GIC of the γ-FeOOH@Fe2O3/CF/EP composite (0.914 ​kJ/m2) is also significantly increased by 88.8% and 51.8% compared to that of CF/EP and the corresponding composite without magnetic field induction, respectively.

A Spin-Valve GMR Based Sensor with Magnetite@silver Core-Shell Nanoparticles as a Tag for Bovine Serum Albumin Detection

The availability of rapid-portable instruments to monitor the bovine serum albumin (BSA) concentration is vital in the early detection of disease. In this research, an original biosensing method based on a spin-valve giant magnetoresistance as a transducer and magnetite@silver core–shell magnetic nanoparticles (MNPs) as a tag has been proposed for detecting BSA. The synthesized magnetite@silver MNPs tag size is ≈15 nm with ≈52 emu g−1 of saturation magnetization. This proposed biosensor performs rapid detection of BSA through the shifting of the switching magnetic field and the increasing of the output voltage. The effectivity of the sensor in monitoring the BSA concentration was shown by a strong linear correlation with ≈0.06 mV/(mg/ml) of the sensitivity and ≈0.44 mg ml−1 of the detection limit. Moreover, the measurement result can be acquired rapidly up to 1 min with low external magnetic field assistance. Therefore, this biosensing technique can be promoted as a real-time portable biosensor.

Controlling metallic Co0 in ZIF-67-derived N-C/Co composite catalysts for efficient photocatalytic CO2 reduction

An efficient photocatalytic CO2 reduction has been reported in ZIF-67-derived-Co nanoparticles (NPs) encapsulated in nitrogen-doped carbon layers (N-C/Co). This work demonstrates that the pyrolysis temperature is crucial in tuning the grain size and components of metallic Co0 of N-C/Co composite catalysts, which optimizes their photocatalytic activities. Syntheses were conducted at 600, 700, and 800°C giving the N-C/Co-600, N-C/Co-700, and N-C/Co-800 samples, respectively. N-C layers can well wrap the Co NPs obtained at a low pyrolysis temperature (600°C) owing to their smaller grains than those of other samples. A high metallic Co0 content in the N-C/Co-600 sample can be attributed to the effective inhibition of surface oxidation. By contrast, the surface CoOx oxides in the N-C/Co-700 and N-C/Co-800 samples cover inside Co cores, inhibiting charge separation and transfer. As a result, the N-C/Co-600 sample yields the best photocatalytic activity. The carbon monoxide and hydrogen generation rates are as high as 1.62 × 104 and 2.01 × 104 µmol g−1 h−1, respectively. Additionally, the Co NPs make composite catalysts magnetic, enabling rapid and facile recovery of catalysts with the assistance of an external magnetic field. This work is expected to provide an instructive guideline for designing metal-organic framework-derived carbon/metal composite catalysts.

Accelerating vinegar aging by combination of ultrasonic and magnetic field assistance

Most fermented foods need a natural aging process to enrich desired flavours. This process is normally the bottleneck for cost-effective production. Therefore, it is desirable to accelerate the process and obtain products with the same flavour profile. Here, we used physical interventions (ultrasonic field, alternating magnetic field, or combination of both) to assist the aging process with naturally brewed vinegar as a case example. Flavour profiles of different physical-assisted aging process were compared with that of the naturally aged vinegar by using gas-chromatography mass-spectrometry (GC–MS) and electronic nose. Principal component analysis (PCA) and Pearson correlation analyses show that ultrasonic and alternating magnetic fields treatment could accelerate the aging process of vinegar. The highest accelerating aging effect was combination of ultrasonic and magnetic field followed by individual ultrasonic or magnetic field and natural process (combination of ultrasonic and magnetic field > ultrasonic or magnetic field individual > natural process). These results suggest that physical field intervention could potentially be used for acceleration of aging of fermented products without affecting flavour quality.

Three-dimensional flower-like FeCoNi/reduced graphene oxide nanosheets with enhanced impedance matching for high-performance electromagnetic wave absorption

Nanostructured magnetic metal/reduced graphene oxide (rGO) composites, benefiting from well-performed losses including high dielectric/magnetic losses, have garnered considerable interest as advanced microwave absorbers (MAs) in recent years. Optional approaches of unique trimetallic/rGO nanostructures, however, are still limited to attain high electromagnetic (EM) absorption and broad bandwidth as well as improved impedance matching. Herein, porous flower-like FeCoNi/rGO nanosheets, synthesized via magnetic-field-assisted (MFA) reduction, presents facilitated microwave absorption performance. The zigzag-like attachments of neighbored nanosheets constitute the porous flower-like architecture; average thickness of the nanosheets is 5–20 nm. The reduction process, determined by appropriate GO dosage, plays a key role to tune geometry and distribution of the flower-like nanosheet structures. The optimal sample, owning a relatively high surface area (157.3 m2 g−1), achieves an impressive reflection loss (RL) intensity of − 75.95 dB and its maximum effective absorption bandwidth (RL ≤ −10 dB) is up to 4.69 GHz, along with improved impedance matching. This work provides a facile and alternative route for exploring other novel nanoalloy-based MAs.

Reaction kinetic of fine Fe2O3 particles assisted by magnetic field in a fluidized bed reactor

In this study, fluidization and hydrogen reduction of fine Fe2O3 particles with magnetic field were investigated. Fine Fe2O3 particles, belonging to Geldart group C, undergo heterogeneous fluidization by conventional fluidization. The agglomeration of products during conventional fluidization of fine Fe2O3 particles was verified, and the pressure drop showed no tendency. The pressure drop stabilized, the magnetic field caused the interparticle force to decrease. High-quality Products without agglomeration were produced under the influence of a magnetic field. With the assistance of the magnetic field, the products showed chain structure after hydrogen reduction. Analysis based on a shrinking core model confirmed that oxygen and iron were distributed on the surface and in the center of the particles, respectively. Studies on the problems associated with conventional fluidization, improvement of magnetic field assisted fluidization and reduction were conducted.

Prototype Design of a Domain-Wall-Based Magnetic Memory Using a Single Layer La0.67Sr0.33MnO3 Thin Film.

Magnetic field-free, nonvolatile magnetic memory with low power consumption is highly desired in information technology. In this work, we report a current-controllable alignment of magnetic domain walls in a single layer La0.67Sr0.33MnO3 thin film with the threshold current density of 2 × 105 A/cm2 at room temperature. The vector relationship between current directions and domain-wall orientations indicates the dominant role of spin-orbit torque without an assistance of external magnetic field. Meanwhile, significant planar Hall resistances can be readout in a nonvolatile way before and after the domain-wall reorientation. A domain-wall-based magnetic random-access memory (DW-MRAM) prototype device has been proposed.

Development of Magnetic Field-Assisted Single-Point Incremental Forming

Single Point Incremental Forming (SPIF) has recently introduced the concept of material formability enhancement through localized deformation. Since material is processed by means of a pin tool attached to spindle, physical interference (especially in vertical direction) limits attainable shapes with the conventional process. The aim of the following work is to increase the variety of achievable geometries with SPIF through in-process magnetic field assistance. An innovative configuration managing SPIF tool movement using magnetic force is proposed. With this in mind, a magnet configuration was designed to generate a vertical load able to plastically deform a 0.5 mm thick AA1100 aluminum sheet. Experiments were carried out to prove the concept by manufacturing a truncated cone; the results demonstrated the feasibility of Magnetic Field-Assisted SPIF.

An efficient, cost-effective, and magnetically recoverable copper catalyst for O-arylation of phenols with aryl halides in choline chloride-based deep eutectic solvents

Silica-coated magnetite nanoparticles were functionalized with aminopropylsilyl groups and then condensed with 2-benzoylthiophene to produce a NS Schiff base chelating ligand for complexation of Cu (II) species. Characterization of the synthesized nanocomposite was performed by several spectroscopic and microscopic analyses to reveal its physical and chemical properties. It was applied as an efficient heterogeneous catalyst in promoting O-arylation reaction of phenols with aryl halides for the synthesis of diaryl ethers using deep eutectic solvents (DESs) based on choline chloride as reaction media. The catalyst and DES could be easily recycled up to five times without a significant effect on the reaction progress. The use of green and recoverable reaction medium, easy work-up, easy separation of the catalyst with the assistance of an external magnetic field, short reaction times, and high yields of products are the main merits of this protocol.