Assistance Of Magnetic Field Research Articles

Preparation of high aspect ratio nickel oxide nanowires and their gas sensing devices with fast response and high sensitivity

NiO p-type semiconducting nanowires with high aspect ratios up to approximately 2000 have been prepared by chemical reduction under assistance of magnetic fields and subsequent heat treatment method. The diameter of NiO nanowires is about 150 nm and the length can be up to 300 μm. Ni nanowires have been prepared from a structure of Ni nanospheres at atmospheric pressure. Transformation from Ni nanowires to NiO semiconducting nanowires via in situ chemical oxidation process in open air have been conducted by undergoing a process of an amorphous oxidation. Heat treatment results in significant influence on the grain size in the NiO nanowire structure. NiO nanowires with crystalline grain size of about 12 nm is characteristic with a band gap energy of about 4.20 eV, which is larger than the bulk NiO material (3.65 eV). Meanwhile, we find that the optical band gap energy gradually increases with the decrease of the crystalline grain size. NiO nanowires with different grain sizes have been used to fabricate arrays for a gas sensor under an external magnetic field. NH3 gas sensing capability at room temperature by NiO nanowire arrays is characteristic for its high sensitivity, fast response, rapid recovery and good reproducibility.

Fast magnetization switching in GaMnAs induced by electrical fields

We study the electrical field induced magnetization reversal in a GaMnAs thin film magnet at the nanosecond scale. Quasi-static electrical fields deplete partially the magnetic material, reducing its magneto-crystalline cubic anisotropy and affecting its transport properties. We demonstrate that electrical field pulses can trigger the nucleation of domains with reversed magnetization. Pulse durations of 2.5 ns are enough to induce the nucleation, indicating precessional effects in the dynamical magnetic response. Full reversal can be obtained with 10 ns and 3 V and the assistance of magnetic fields substantially lower than the coercivity of the material in the absence of gate voltage.

Nano-finishing techniques: a review

The quality of surface is one of the significant parameters which affects the life and functionality of any product. Many products require nano-level surface finish as their functional indispensability. Those processes having flexible finishing tool can be employed for such type of components. These finishing processes can be classified into two categories: with and without magnetic field assistance. The former includes magnetic abrasive finishing, magnetorheological finishing, and allied processes, and the latter includes abrasive flow finishing. This article reports the critical review of mainly three processes: abrasive flow finishing, magnetorheological finishing, and magnetorheological abrasive flow finishing. In this article, the issues that need attention of the researchers have been categorically mentioned. This article provides a comprehensive literature review of magnetorheological finishing process in terms of rheological characterization of magnetorheological fluid, experimental investigation, theoretical analysis, and applications. This article deals with various advancements in abrasive flow finishing and hybrid processes. The developments in magnetorheological abrasive flow finishing and its allied processes have been discussed in detail. By suitable modification of magnetorheological abrasive flow finishing process, it can achieve surface finish up to nano-meter on different materials such as brass, aluminium, stainless steel, and silicon-nitride.

Magnetic properties of Cr‐doped ZnO nanorods fabricated by hydrothermal method in a high pulsed magnetic field

AbstractCr‐doped ZnO diluted magnetic semiconductor (DMS) nanorods with nominal composition of 1 at.% were synthesized by a hydrothermal method with the assistance of a high pulsed magnetic field (HHPMF). All the Cr‐doped ZnO samples obtained with or without the applied high magnetic field exhibited room‐temperature ferromagnetic behavior. It is observed that the high magnetic field plays an important role in saturation magnetization of the samples. The effects of high magnetic field on the morphology, structure, and magnetic properties of the samples were discussed.

Machining Characteristics of Magnetic Force-Assisted Electrolytic Machining for Polycrystalline Silicon

Wire electrical discharge machining (WEDM) of polycrystalline silicon (polysilicon) involves high-temperature melting that easily produces cracks on the silicon surface. This paper studies improvements of cracks and craters on surface of polysilicon after wire electrical discharge machining (WEDM) by magnetic force-assisted electrolytic machining (MFA-EM). The effects of different MFA-EM parameters on material removal and surface roughness are explored to understand the machining characteristics of MFA-EM and how magnetic field assistance contributes to high-efficiency and high-quality machining. Experimental results show that compared with standard EM, MFA-EM can achieve better machining efficiency and surface quality because MFA-EM can effectively enhance electrolyte circulation and replenishment, which contributes to better machining stability.

Formation of magnetic glass in calcium-doped YBaCo2O5.5cobaltites

The d.c. magnetization and magnetic relaxation studies of the calcium doped samples, Y0.95Ca0.05BaCo2O5.5 and YBa0.95Ca0.05Co2O5.5, show the existence of a magnetic glass like behaviour in the family of cobaltites for the first time. Our investigations reveal glass-like arrest of kinetics at low temperature which prevents the system from reaching its magnetic ground state. We show that the low temperature state of these calcium doped phases, which consists of coexisting antiferromagnetic and ferro (or ferri) magnetic phase fractions, can be tuned in a number of ways. Our observations establish that the low temperature state of this oxide is not in thermal equilibrium. The glassy state is formed with the assistance of an external magnetic field, which makes it distinctly different from the more well known metastable state, the spin glass state. The cooling field can tune the fractions of the coexisting phases, and the glass-like state formed at low temperature can also be devitrified by warming the sample. The role of Ca doping in the appearance of these phenomena is discussed in terms of phase separation, involving Co3+ disproportionation into Co4+ ferromagnetic clusters and Co2+ antiferromagnetic clusters.

Magnetic-Field-Assisted Assembly of Layered Double Hydroxide/Metal Porphyrin Ultrathin Films and Their Application for Glucose Sensors

The ordered ultrathin films (UTFs) based on CoFe-LDH (layered double hydroxide) nanoplatelets and manganese porphyrin (Mn-TPPS) have been fabricated on ITO substrates via a magnetic-field-assisted (MFA) layer-by-layer (LBL) method and were demonstrated as an electrochemical sensor for glucose. The XRD pattern for the film indicates a long-range stacking order in the normal direction of the substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the MFA LDH/Mn-TPPS UTFs reveal a continuous and uniform surface morphology. Cyclic voltammetry, impedance spectroscopy, and chronoamperometry were used to evaluate the electrochemical performance of the film, and the results show that the MFA-0.5 (0.5 T magnetic field) CoFe-LDH/Mn-TPPS-modified electrode displays the strongest redox current peaks and fastest electron transfer process compared with those of MFA-0 (without magnetic-field) and MFA-0.15 (0.15 T magnetic field). Furthermore, the MFA-0.5 CoFe-LDH/Mn-TPPS exhibits remarkable electrocatalytic activity toward the oxidation of glucose with a linear response range (0.1-15 mM; R(2) = 0.999), low detection limit (0.79 μM) and high sensitivity (66.3 μA mM(-1) cm(-2)). In addition, the glucose sensor prepared by the MFA LBL method also shows good selectivity and reproducibility as well as resistance to poisoning in a chloride ion solution. Therefore, the novel strategy in this work creates new opportunities for the fabrication of nonenzyme sensors with prospective applications in practical detection.

Pristine and Hybrid Nickel Nanowires: Template-, Magnetic Field-, and Surfactant-Free Wet Chemical Synthesis and Raman Studies

Nickel nanowires of high purity and various aspect ratios were synthesized by a wet chemical reduction method without the assistance of surfactants, templates, and external magnetic field. The observed unique optical absorption features of nickel nanowires are highly dependent on the nanowire dimensions. In order to tailor the physical and chemical properties of the nanowires, we have incorporated functionalities in the form of tellurium and zinc oxide coating on them by overgrowth processes using simple wet chemical reactions. The pristine and functional nanowires were characterized by different microscopic and spectroscopic techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), confocal Raman microscopy, X-ray diffraction spectroscopy (XRD), and UV−visible spectroscopy. Our system provides additional details into the growth of anisotropic Ni nanowires, especially in the absence of surfactants, templates, and external magnetic field. We have also demonstrated surface-enhanced Raman scattering (SERS) activity of the Ni nanowires using crystal violet as the probe molecule.

Folate and iron difunctionalized multiwall carbon nanotubes as dual-targeted drug nanocarrier to cancer cells

A nanomaterial, folate and iron difunctionalized multiwall carbon nanotube (FA-MWCNT@Fe), has been synthesized by conjugating folate and iron nanoparticles with oxidized multi-walled carbon nanotubes, and applied as a dual-targeted drug nanocarrier to deliver doxorubicin into HeLa cells with the assistance of an external magnetic field. The prepared FA-MWCNT@Fe was characterized by X-ray diffraction, transmission electron microscopy and infrared spectroscopy. This nanocarrier has a sufficient load capacity (doxorubicin/FA-MWCNT@Fe, 32 μg/mg) and a prolonged release property controlled by near infrared radiation. It also demonstrated both biologically (active) and magnetically (passive) targeting capabilities toward HeLa cells in vitro with ca. 6-fold higher delivery efficiency of doxorubicin than free doxorubicin.

Magnetic-field-assisted assembly of CoFe layered double hydroxide ultrathin films with enhanced electrochemical behavior and magnetic anisotropy

Magnetic films based on CoFe LDH nanoplatelets and porphyrin anions were fabricated by the layer-by-layer assembly technique with an assistance of an external magnetic field, which show enhanced electrochemical behavior and magnetic anisotropy.

Field-Assisted Synthesis and Electromagnetic Properties of Aligned Magnetic Nanostructures by γ-Irradiation Induced Reduction

We here demonstrate the preparation of magnetic nanostructures (Co, Ni) with aligned morphologies through a magnetic field-assisted γ-irradiation route. It is found out that a proper magnetic field can induce the prepared magnetic nanoparticles to align into well-defined stick or chain structures, where randomly dispersed nanoparticles are obtained without the application of magnetic field. The alignment of the magnetic nanoparticles gives rise to increased magnetization and coercivity due to the enhancement in shape anisotropy. Meanwhile, compared with the scattered nanoparticles, stronger electromagnetic wave absorption properties can also be realized in the aligned nanostructures, caused by the geometrical effect. We think this alignment of magnetic nanoparticles into specific structures under the assistance of magnetic field may be appealing in improving the electromagnetic wave absorptions that are not accessible in randomly dispersed particles.

Aluminum matrix composites reinforced by in situ Al 2O 3 and Al 3Zr particles fabricated via magnetochemistry reaction

Aluminum matrix composites reinforced by in situ Al 2O 3 and Al 3Zr particles are fabricated from A356-Zr(CO 3) 2 system via magnetochemistry reaction, and the morphologies, sizes and distributions of the in situ particles as well as the microstructures, mechanical mechanisms of the composites are investigated by XRD, SEM, TEM and in situ tensile tests. The results indicate that with the pulsed magnetic field assistance, the morphologies of the in situ particles are mainly with ball-shape, the sizes are in nanometer scale and the distributions in the matrix are uniform. The interfaces between the in situ particles and the aluminum matrix are net and no interfacial outgrowth is observed. These are due to the strong vibration induced by the applied magnetic field in the aluminum melt, which in turn, accelerates the melt reactions. The effects of the magnetic field on the above contributions are discussed in detail.

Template-free Synthesis of One-dimensional Cobalt Nanostructures by Hydrazine Reduction Route.

One-dimensional cobalt nanostructures with large aspect ratio up to 450 have been prepared via a template-free hydrazine reduction route under external magnetic field assistance. The morphology and properties of cobalt nanostructures were characterized by scanning electron microscopy, X-ray diffractometer, and vibrating sample magnetometer. The roles of the reaction conditions such as temperature, concentration, and pH value on morphology and magnetic properties of fabricated Co nanostructures were investigated. This work presents a simple, low-cost, environment-friendly, and large-scale production approach to fabricate one-dimensional magnetic Co materials. The resulting materials may have potential applications in nanodevice, catalytic agent, and magnetic recording.

Oxidative Desulfurization of Fuel Oil with Hydrogen Peroxide Catalyzed by Keggin-type Polyoxotungstate in a DC Magnetic Field

The oxidation of sulfur-containing compounds was conducted in a DC magnetic field-assisted system, composed of model compound or diesel, 30 wt% hydrogen peroxide, and an iron mono-substituted Keggin-type heteropolytungstate [(C4H9)4N]4 [PW11Fe(H2O)O39] catalyst. By combining oxidative desulfurization (ODS) in a magnetic field and acetonitrile extraction, when magnetic field intensity was at 17.3 mT, the removal efficiency of the model compound dibenzothiophene (DBT) in petroleum ether with 1,000 ppm S can reach 98% at 70°C within 30 min with O/S ratio = 3 and catalyst dosage 5%, with 2% increase over that without magnetic field assistance. Under the same reaction conditions, the sulfur level of diesel oil was reduced from 5,647 to 508 ppm. This shows that the DC magnetic field facilitates the oxidation of sulfur-bearing compounds, which allowed greater sulfur removal efficiency under milder reaction conditions.

Preparation of Fe3O4@Au nano-composites by self-assembly technique for immobilization of glucose oxidase

Superparamagnetism amination nanocrystals Fe3O4 with 3-aminopropyltriethyloxy silane (APTES) were prepared by modified co-precipitation method. Next, 4-5 nm gold nanoparticles, prepared by classical Frens procedure, were coated on the surface of the amination Fe3O4 by self-assembly technology. The prepared Fe3O4@Au nanocomposite particles were investigated by transmission electron microscopy (TEM), UV-vis, infrared spectrum (FT-IR), and vibrating sample magnetometer (VSM) in order to elucidate the morphology, optics and magnetic properties of the nanocomposites. Their uniform distribution of particle size, which is about 15 nm, and good magnetic responsiveness were observed. In view of the fact that Fe3O4 owns superparamagnetism and that nano-gold can readily combine with biological molecules, glucose oxidase (GO x ) was chosen as a model to penetrate the condition of immobilizing enzyme, and enzymatic properties of resultant immobilized enzyme were studied as well. By systematic optimization, we established that at 28°C, and pH (5.5) and when mole ratio of Fe3O4:HAuCl4 was 0.5:1, the immobilization provided the best results. Finally, we are glad to find that the immobilized enzyme exhibits excellent thermostability in addition to its better stability than free enzyme. Thus, herein described immobilized enzyme could be used repeatedly with the assistance of an external magnetic field.

Magnetic field assisted Fenton reactions for the enhanced degradation of methyl blue

Magnetic field was tentatively introduced into Fenton reactions system for the degradation and discoloration of methyl blue as the represent of organic chemical dye, which was a bio-refractory organic pollutant in industry wastewater. It was found that under optimal Fenton reaction conditions, with the assistant of magnetic field in Fenton reactions, the degradation rate of methyl blue, the decomposition rate of H 2O 2 and the conversion rate of Fe 2+ were accelerated, the extent of them would be improved by the increase of magnetic field intensity. Meanwhile, the mineralization of methyl blue (COD cr) was improved by over 10% with magnetic field.

(Al 2O 3 + Al 3Zr)/A356 nanocomposites fabricated by magnetochemistry in situ reaction

The (Al 2O 3 + Al 3Zr)/A356 nanocomposites are fabricated via magnetochemistry in situ reaction. The interface between the in situ particles and the aluminum matrix, the mechanical properties and behaviors are investigated by SEM, TEM and in situ tensile observations. The results indicate that the interfaces are net and no interfacial outgrowth observed; the values of the tensile strength, yield strength and the Brinell Hardness are reached 393.8 MPa, 339.74 MPa and 139.8 kgf/mm 2, respectively with the pulsed magnetic field assistance; the cracks are initiated by the dislocation accumulation effects, the cavity-nucleation effects and the matrix flaw effects; the crack growth behaviors are very much dependent on the microstructure of the composites. The fracture model of the composites is established and discussed.

The influence of magnetic confinement in DC abnormal-glow discharges

The DC abnormal-glow discharges with magnetic field assistance near the cathode targets are particularly useful in magnetron sputtering and are extensively used in industrial plasma processing applications [Thornton JA. J Vacuum Sci Technol 1978; 15(2): 171–177]. In this work, an experimental study of the magnetic field influence on planar magnetron abnormal-glow discharges of argon on copper targets is presented. A confinement power parameter C B is proposed and takes into account the useful volume and the average parallel component of the magnetic induction in that volume. The I– V characteristics at constant pressure and at several confinement power values are discussed in the scope of the Thornton empirical law, I= kV n . The evolution of n and log( k), is neither monotonic with pressure, nor with confinement power. A linear relation between n and log( k ) was found and allows to present an empirical expression I = a ( bV ) n for the I– V characteristics with two constants a and b and only n as free parameter.

Spin-polarized current-induced magnetization reversal in perpendicularly magnetized L1-FePt layers

Current-induced magnetization reversal of perpendicularly magnetized layers was studied in current-perpendicular-to-plane giant magnetoresistance pillars with L10-FePt (001) layers. The FePt layers exhibited strong perpendicular magnetic anisotropy of the order of 107erg∕cm3. A series of magnetoresistance curves after applying pulse currents with different current densities showed that current-induced magnetization reversal from an antiparallel to a parallel alignment occurred at the current density of the order of 108A∕cm2 with the assistance of magnetic field.

Stretching of a confined ferrofluid: Influence of viscous stresses and magnetic field

An analytical investigation is presented for the stretch flow of a viscous Newtonian ferrofluid highly confined between parallel plates. We focus on the development of interfacial instabilities when the upper plate is lifted at a described rate, under the action of an applied magnetic field. We derive the mode-coupling differential equation for the interface perturbation amplitudes and study both linear and nonlinear flow regimes. In contrast to the great majority of works in stretch flow we take into account stresses originated from velocity gradients normal to the ferrofluid interface. The impact of such normal stresses is accounted for through a modified Young-Laplace pressure jump interfacial boundary condition, which also includes the contribution from magnetic normal traction. We study how the stability properties of the interface and the shape of the emerging patterns respond to the combined action of normal stresses and magnetic field, both in the presence and absence of surface tension. We show that the inclusion of normal viscous stresses introduces a pertinent dependence on the initial aspect ratio, indicating that the number of fingers formed would be overestimated if such stresses are not taken into account. At early linear stages it is found that such stresses regularize the system, acting as an effective interfacial tension. At weakly nonlinear stages we verified that normal stresses reduce finger competition, which can be completely suppressed with the assistance of an azimuthal magnetic field. We have also found that the magnetic normal traction introduces a purely nonlinear contribution to the problem, revealing the key role played by the magnetic susceptibility in the control of finger competition.