Direct Current Magnetic Field Research Articles

Multifunctional two-dimensional photonic crystal optical component based on magneto-optical resonator: nonreciprocal two-way divider-switch, nonreciprocal 120 deg bending-switch, and three-way divider

We suggest and analyze a compact nonreciprocal optical four-port based on a magneto-optical resonator in two-dimensional photonic crystal, which can fulfill many functions. This component can be used in three regimes: first, with magnetization by a direct current (DC) magnetic field +H0, second, with magnetization by the DC magnetic field −H0, and finally, with magnetization by the DC magnetic field +H1. In the first regime, the four-port ensures equal division of the input signal between two output ones simultaneously providing protection of the generator in the input port from harmful reflected signals in the output ports; this can also be used as a switch by reversing +H0 to −H0. In the second regime, the same four-port fulfills 120-deg bending and it provides protection of the generator in the input port from reflected signals; it can also be used as a switch by reversing −H0 to +H0. In the third regime, with DC magnetic field +H1, the device can be used as a three-way divider with equal division to the output ports. We analyze the scattering matrix of this component and discuss the physical mechanisms of its functioning. In addition, computational simulations were performed and their results confirm our theoretical predictions.

Cube Texture Formation in Fe–50 % Ni Thin Tapes Under Annealing in DC High Magnetic Field

The main purpose of the work is to study the recovery and recrystallization processes in cold-rolled tapes of the Ni48.8Fe51.2 alloy subjected annealing under high magnetic fields up to 20T. In the course of primary recrystallization without magnetic field, in the tapes made of this alloy, there forms a sufficiently sharp cube texture, which makes it possible to use these tapes for epitaxial deposition on them of high-temperature superconductors (HTS). In the work presented, the rolled tapes are used as a model material for investigation of structure transformations upon a new treatment mode—annealing in high direct current magnetic field. Preliminary annealings in magnetic field and, for comparison, without it were performed at temperatures both above and below the Curie temperature and, at the same time, the onset temperature of primary recrystallization. It is shown that as a result of the final annealing without magnetic field at an elevated temperature, which provides the primary recrystallization and normal grain growth, in the recrystallization texture of tapes that underwent a preliminary annealing at the temperature below the Curie point, there is observed a noticeable increase of the volume fraction of grains with the easy magnetization axis . Moreover, the retardation of recovery processes during magnetic annealing was found.

Ethical considerations in using brain stimulation to treat eating disorders.

Eating disorders (EDs), such as anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED) are characterized by pathological eating behaviors and body image disturbance. These disorders are associated with high levels of mortality and morbidity, as well as significantly impaired quality of life (Arcelus et al., 2011). EDs are often associated with young adulthood, with the disorder typically being first diagnosed when the person is 15–19 years old (Hoek and van Hoeken, 2003; Hudson et al., 2007). Recently, there has been increased interest in the neurobiology of EDs as an insight into the mechanisms of pathological eating behavior, and as a potential avenue for treatment (Kaye et al., 2010). Brain-based interventions for EDs have in the past involved highly invasive deep-brain stimulation (DBS), in which surgically implanted electrodes deliver electrical pulses to brain areas such as the cingulate cortex (Israel et al., 2010) or the nucleus accumbens (Wu et al., 2013). These surgeries have proved reasonably effective in the small number of reported cases. However DBS has a number of problems that make it less attractive as a treatment option: DBS exposes the person to the risks of surgery; the potential side-effects are more serious; and it is difficult to adjust or to reverse the treatment. For these reasons, there is much interest in a treatment that modulates brain activity but that does not expose the patient to such serious side-effects. There has recently been an increase in interest in the use of so-called non-invasive brain stimulation to treat EDs. These techniques, principally transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), use magnetic or electric fields to transfer energy across the skull, and so to modulate neural activity. Here, we explore the rationale for using TMS/tDCS in EDs, and argue that many ethical and safety issues must be clarified before widespread adoption of these techniques is possible.

Electronic structure and slow magnetic relaxation of low-coordinate cyclic alkyl(amino) carbene stabilized iron(I) complexes.

Cyclic alkyl(amino) carbene stabilized two- and three-coordinate Fe(I) complexes, (cAAC)2FeCl (2) and [(cAAC)2Fe][B(C6F5)4] (3), respectively, were prepared and thoroughly studied by a bouquet of analytical techniques as well as theoretical calculations. Magnetic susceptibility and Mössbauer spectroscopy reveal the +1 oxidation state and S = 3/2 spin ground state of iron in both compounds. 2 and 3 show slow magnetic relaxation typical for single molecule magnets under an applied direct current magnetic field. The high-frequency EPR measurements confirm the S = 3/2 ground state with a large, positive zero-field splitting (∼20.4 cm(-1)) and reveal easy plane anisotropy for compound 2. CASSCF/CASPT2/RASSI-SO ab initio calculations using the MOLCAS program package support the experimental results.

Tuning the structures of manganese(III) (Schiff base) complexes: Syntheses, crystal structures and magnetic properties

Four new coordination complexes, [MnIII(3-EtO-salpn)(H2O)(CH3OH)]ClO4 (1), [MnIII(3-EtO-salpn)(H2O)2]·H2O·ClO4 (2), {[MnIII(3-EtO-salpn)(H2O)][FeIII(qcq)(CN)3]}·3H2O·CH3OH·CH3CN (3) and {[MnIII(3-EtO-salpn)(H2O)][FeIII(qcq)(CN)3]}·3H2O·CH3CN (4) (salpn=N,N′-1,2-propylenebis(salicylideneiminato)dianion; qcq=8-(2-quinoline-2-carboxamido)quinoline anion) were synthesized and characterized both structurally and magnetically. The results reveal that complexes 1 and 2 are mononuclear MnIII structures crystallizing in different space groups, while 3 and 4 are dinuclear MnIII–NC–FeIII entities with different local arrangement of the subunits. Interestingly, the structures of these complexes are highly dependent on the reaction conditions though the reaction precursors are the same. Magnetic investigation indicates that intra- and/or intermolecular antiferromagnetic interactions are presented in complexes 1–4. Notably, these weak antiferromagnetic interactions could be overcome by high direct-current magnetic field, showing the field induced metamagnetic behaviors.

A system of phase synchronization of a spin-transfer nano-oscillator

We have studied the dynamics of a filterless phase-synchronization system (PSS) of a spin-transfer nano-oscillator (STNO) generating microwave oscillations in a broad range of frequencies under the effect of direct current and external magnetic field. Bifurcations in the system caused by a change in the frequency detuning of synchronized oscillations are considered. Bands of phase locking and synchronism are determined. The existence of a phase-locking band in the filterless PSS of STNOs basically distinguishes these oscillators from other types of microwave generators.

Numerical simulation of transport phenomena during strip casting with EMBr in a single belt caster

A theoretical investigation of fluid flow, heat transfer and solidification (solidification transfer phenomena, STP) was presented which coupled with direct-current (DC) magnetic fields in a high-speed strip-casting metal delivery system. The bidirectional interaction between the STP and DC magnetic fields was simplified as a unilateral one, and the fully coupled solidification transport equations were numerically solved by the finite volume method (FVM). While the magnetic field contours for a localized DC magnetic field were calculated by software ANSYS and then incorporated into a three-dimensional (3-D) steady model of the liquid cavity in the mold by means of indirect coupling. A new FVM-based direct-SIMPLE algorithm was adopted to solve the iterations of pressure-velocity (P-V). The braking effects of DC magnetic fields with various configurations were evaluated and compared with those without static magnetic field (SMF). The results show that 0.6 T magnetic field with combination configuration contributes to forming an isokinetic feeding of melt, the re-circulation zone is shifted towards the back wall of reservoir, and the velocity difference on the direction of height decreases from 0.1 m/s to 0. Furthermore, the thickness of solidified skull increases uniformly from 0.45 mm to 1.36 mm on the chilled substrate (belt) near the exit.

Grain refinement of pure aluminum by direct current pulsed magnetic field and inoculation

The combined effects of direct current pulsed magnetic field (DC-PMF) and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% (mass fraction) Al–5Ti–B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μm.

A hydrogel-based intravascular microgripper manipulated using magnetic fields

This study presents a magnetic hydrogel-based microgripper that can be wirelessly manipulated using magnetic fields. The proposed device can move freely in liquids when driven by direct current (dc) magnetic fields, and perform a gripping motion by using alternating current (ac) magnetic fields. The device is fabricated from a biocompatible hydrogel material that can be employed for intravascular applications. The actuation mechanism for gripping motions is realized by controlling the exposure dose on the hydrogel composite during the lithography process. The preliminary characterization of the device is also presented. The measurement results show that the gripping motion reached a full stroke at approximately 38°C. By dispersing multiwall carbon nanotubes (MWCNT) into the material, the overall response time of the gripping motion decreases by approximately 2-fold. Device manipulations such as the gripping motion, translational motion, and rotational motion are also successfully demonstrated on a polyvinyl chloride (PVC) tube and in a polydimethylsiloxane (PDMS) microfluidic channel.

Ultralow-Intensity Magneto-Optical and Mechanical Effects in Metal Nanocolloids

Magneto-plasmonics is a designation generally associated with ferromagnetic-plasmonic materials because such optical responses from nonmagnetic materials alone are considered weak. Here, we show that there exists a switching transition between linear and nonlinear magneto-optical behaviors in noble-metal nanocolloids that is observable at ultralow illumination intensities and direct current magnetic fields. The response is attributed to polarization-dependent nonzero-time-averaged plasmonic loops, vortex power flows, and nanoparticle magnetization. This work identifies significant mechanical effects that subsequently exist via magnetic-dipole interactions.

Numerical Simulation of Fluid Flow during Strip Casting with Electromagnetic Braking in the Mold of Single-belt Caster

For theoretically investigating the fluid flow under the influence of various direct-current(DC) magnetic fields in the mold of a single-belt horizontal continuous caster, a three-dimensional(3D) numerical model for describing electromagnetic-solidification phenomena based on finite volume method(FVM) is presented. The bidirectional interactions between transport process and DC magnetic fields are simplified as a unilateral one, and the fully coupled transport equations are numerically solved by indirect-coupling method. The DC magnetic fields with two configurations output by ANSYS as well as two assumed magnetic fields in literatures with different values are taken as external DC magnetic fields for EMBr; the influences of various magnetic fields on flow field are studied by numerical calculation. The results show that 0.2 T magnetic field with fictitious configurations can result in a reasonably flow, and a vertical-type DC magnetic field precedes the horizontal one. The optimal flow field could be achieved when a 0.4 T real DC magnetic field with different configurations applied, which is inferior to the fictitious DC magnetic field due to decay characteristic of a real magnetic field. The calculation model and the methods as well as all results provide the basis and reference for the improvement of the magnetic flow modifier and flow in mold in follow-up study.

Grain Refinement of Mg<sub>97</sub>Y<sub>2</sub>Cu<sub>1</sub> Alloy Solidified with Pulsed Direct Current Magnetic Field

The influences of different pulse voltage, discharging frequency, pouring temperature and mold temperature on marostructure of Mg97Y2Cu1alloy under pulsed direct current magnetic field (PDCMF) were studied and the related mechanism was also discussed. The results show that grains of Mg97Y2Cu1alloy can be refined greatly by PDCMF treatment. Macrostructure of the alloy is changed from coarsened grains to complete fine equiaxed grains. When the pulse voltage is at 0-250V, grain size of the alloy decreases dramatically as pulse voltage increases. When the discharging frequency is at 1-10Hz, grain size of the alloy increases firstly, then decreases, and the turning point is 5 Hz. The change of grain size is not obvious, when the discharging frequency increases from 1 Hz to 5 Hz. When the discharging frequency reaches 10 Hz, the effect of grain refinement is the best. When the mold temperature is at 20-600°C or the pouring temperature is at 660-750°C, grain size of the alloy with PDCMF treatment decreases grossly with the increase of the mold temperature or the pouring temperature. The higher the pouring temperature or the mold temperature, the better the effect of grain refinement with PDCMF treatment.

Frequency dependence of magnetization and giant magneto impedance effect of amorphous wires

The frequency dependence of magnetization process and giant magneto impedance (GMI) effect of Co-rich melt-extracted amorphous wires was studied by Kerr effect and impedance analyzer, respectively. It is demonstrated that the transverse Kerr intensity and the corresponding GMI response increase with increasing frequency, which contributes to the upgraded skin effect. However, the skin depth has a slothful trend with frequency when it is up to the megahertz range, which gives rise to the transformation of magnetization. The process is much more sensitive to the direct current magnetic field and the sensitive change of the circular permeability, and GMI response is observed as its consequence. This proves that the evolution of circumferential magnetization and the corresponding permeability with the direct current magnetic field is the essence of GMI response, and a much more sensitive magnetization promises a better GMI response.

Octanuclear {Ln(III)8}(Ln = Gd, Tb, Dy, Ho) Macrocyclic Complexes in a Cyclooctadiene-like Conformation: Manifestation of Slow Relaxation of Magnetization in the Dy(III) Derivative

The synthesis of a series of macrocyclic, isostructural octanuclear lanthanide complexes [Gd8 (LH2)4 (μ-Piv)4 (η(2)-Piv)4 (μ-OMe)4]·6CH3OH·2H2O (1), [Tb8 (LH2)4 (μ-Piv)4 (η(2)-Piv)4 (μ-OMe)4]4CH3OH·4H2O (2), [Dy8(LH2)4 (μ-Piv)4 (η(2)-Piv)4 (μ-OMe)4]·8CH3OH (3), and [Ho8(LH2)4(μ-Piv)4 (η(2)-Piv)4 (μ-OMe)4]·CH3OH·4H2O (4) have been achieved, using Ln(III) nitrate salts, pivalic acid, and a new multidentate chelating ligand (2E,N'E)-N'-(3-((bis(2- hydroxyethyl)amino)methyl)-2-hydroxy-5-methylbenzylidene)-2-(hydroxyimino) propane hydrazide (LH5), containing two unsymmetrically disposed arms; one side of the phenol unit is decorated with a diethanolamine group while the other side is a hydrazone that has been built by the condensation reaction involving 2-hydroxyiminopropanehydrazide. All the compounds, 1-4, are neutral and are held by the four [LH2](3-) triply deprotonated chelating ligands. In these complexes all the lanthanide ions are doubly or triply bridged via phenolate, alkoxy, and pivalate oxygens. The metal centers are distributed over the 8 vertices of an octagon, resembling a cyclooctadiene ring core. The details of magnetochemical analysis for complexes 1-4 shows that they exhibit antiferromagnetic interactions between the Ln(3+) ions through the phenoxo, alkoxo, and pivalato bridging groups. None of the compounds exhibits slow relaxation of the magnetization at zero applied direct current (dc) magnetic field, which could be due to the existence of a fast quantum tunneling relaxation of the magnetization (QTM). In the case of 3, the application of a small dc field is enough as to fully or partly suppress the fast and efficient zero-field QTM allowing the observation of slow relaxation above 2 K.

Electromigration in Giant Magnetoresistance Spin Valve Read Sensors Under Pulsed DC Magnetic Field: An Analytical and Numerical Study

A theoretical model is proposed to investigate the electromigration (EM) behavior in giant magnetoresistance spin valve (GMR SV) read sensors under pulsed direct current (dc) magnetic field during sensor operation. It was found that the externally applied magnetic field gives rise to a more severe Joule heating and consequently raises the device temperature leading to EM acceleration. Black's equation was modified based on Green's function method and the Boltzmann equation to more precisely interpret the EM mean time to failure (MTTF) of GMR SV read sensors under pulsed dc magnetic field. The physical validity of this proposed model was confirmed by the comparisons with experimental results.

Synthesis, crystal structure and magnetic properties of dinuclear NiIILnIII complexes based on a flexible polydentate ligand

The synthesis and characterization of three isomorphous complexes [NiII(L)LnIII(DBM)₃] (Ln = Gd (1·2.5CH₃CN·0.5H₂O), Tb (2·2CH₃CN·0.5MeOH), and Dy (3·2CH₃CN·0.5MeOH·0.5H₂O)) are reported (H₂L = N,N'-dimethyl-N,N'-(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine, DBM⁻ = anion of 1,3-diphenylpropane-1,3-dione). The flexible ligand L²⁻ contains an N₂O₂-inner and an O₄-outer coordination site. There are diphenoxo bridges between NiII and LnIII ions in these complexes. The remaining coordination sites are occupied by DBM⁻ anions. Direct current (dc) magnetic susceptibility measurements indicate the presence of intramolecular ferromagnetic interactions in desolvated complexes 1-3. The magnetic coupling constant JNiGd in complex 1 is estimated to be 1.11 cm⁻¹ (H = -2JNiGdSNiSGd). Alternating current (ac) magnetic susceptibility studies reveal that complexes 2 and 3 show frequency-dependent out-of-phase signals, which indicate that they exhibit SMM behavior. The energy barriers for complexes 2 and 3 under a 2 kOe applied direct current (dc) magnetic field are estimated from Arrhenius plots to be 14.4 and 11.3 K, respectively.

Effect of obliqueness of external magnetic field on the characteristics of magnetized plasma wakefield

A direct three-dimensional model to study the wakefield in underdense magnetized plasma is introduced. The model is based on an analytic procedure by Laplace transformation for calculating the magnetized plasma wake equations. Wakefield is excited using a high-intensity ultrashort laser beam. In the presence of external magnetic field perpendicular to the direction of the laser pulse propagation direction, plasma electrons rotate around the magnetic field lines, leading to the generation of an electromagnetic component of the plasma wakes at plasma frequency. This component is polarized perpendicularly to the direct current magnetic field lines and propagates in the forward direction and normal direction with respect to the laser pulse propagation direction, both perpendiculars to the direction of the applied magnetic field. Intensity of the radiation in different plasma densities and different magnetic field strengths has been observed.

Effectiveness of using a magnetic compound fluid with a pulsed magnetic field for flat surface polishing

The effects of the frequency of a pulsed magnetic field on flat polishing were investigated to obtain basic data for increasing the performance and precision of polishing using MCFs. We clarified that the profile curves after polishing differ for a direct-current magnetic field and for a pulsed magnetic field and flattening occurred over a wide range when the frequency of a pulsed magnetic field is 0.1 Hz.

Levitated Liquid Dynamics in Reduced Gravity and Gravity-Compensating Magnetic Fields

Dynamic models are used to investigate the behavior of liquid droplets suspended in alternating current and direct current magnetic fields in microgravity and in various configurations providing conditions similar to microgravity. The realistic magnetic fields of solenoidal coils are used for the modeling experiments with electrically conducting (liquid silicon or metal) droplets. At high values of magnetic field, some oscillation modes are damped quickly, while others are modified with a considerable shift of the oscillating droplet frequencies and the damping constants from the nonmagnetic case. On a larger scale, the models are used to investigate the melting and heating process of reactive materials. It is demonstrated how 1 kg of liquid titanium in a traditional “cold” crucible-type furnace can be fully levitated without contact to wall to achieve high superheat of the melt.

Variation of ferroelectric properties in (Bi,Pr)(Fe,Mn)O3/SrRuO3-Pt/CoFe2O4 layered film structure by applying direct current magnetic field

We report the preparation of (Bi,Pr)(Fe,Mn)O3(BPFM)/SrRuO3 (SRO)-Pt/CoFe2O4(CFO) layered film structure on (100) SrTiO3 substrate by pulsed laser deposition method and their structural and electrical properties. Favorable ferroelectric properties of BPFM were observed in the layered film structure with (100)-oriented growth of BPFM, SRO, and CFO. Variation of polarization vs electric field loops of BPFM by applying DC magnet field was observed, and the remnant polarization was found to increase by 3% with increasing the applied magnetic field from 0 to 10 kOe. The magnetoelectric coefficient in the present structure was estimated to be 1.5 V/(cmOe).