External Magnetization Research Articles

Characterization of signal integrity due to pitch-roll-yaw rotation tolerance in magnetic position sensing systems

Magnetoresistive sensor is commonly used as a read head to detect sine and cosine waveforms from magnetic patterned medium for determining precision position in engineering applications. The sensor utilizes its magnetoresistivity ability to change its resistance under the influence of magnetic fields. The resistance changes proportionally to square of the sine of the angle between the magnetization vector ( ${M}$ ) and current flow vector ( ${I}$ ). Therefore, the assembly tolerances, such as the pitch, roll, and yaw rotations, between the sensor and the medium would cause angle changes with respect to external magnetic field and magnetization vector, leading to distorted waveforms in microprocessor that result in undesirable subdivision position error. In this paper, parameter studies are conducted with results validated by experiment in determining the characteristic relationship between the assembly tolerances on the measured magnetic signals for manufacturing and real-time dynamic control applications.

A technique and installation for studying electrophysical properties of high-temperature superconductors

This paper presents an experimental exploration of the electrophysical properties of high-temperature superconductors that is based on the determination of the constitutive equation parameters for the combined model with two sources of electromagnetic field: current density and magnetization. It involves a series of experiments in different external magnetic fields and various transition modes to the superconducting state that allows the individual field sources to be distinguished. Since conditions that would enable us to maintain a homogenous current density distributions and magnetization under varying external magnetic induction in the HTSs are not available, the magnetic field parameters and its sources in the samples are determined via computational and experimental methods, in which the magnetic field parameters in the sample are calculated using their values out of the sample. A special laboratory installation equipped with the required measuring tools and magnetic system to create a controlled external magnetic field with the magnetic flux density of 1.5 T is constructed for the practical implementation of the experimental research technique.

Strong spintronic magnetoelectric effect in layered magnetic metamaterial

It is shown that external magnetic field or magnetization induces electric polarization of microscopic isolated magnetic/non-magnetic hybrid structures due to the spin-dependent electron redistribution and mutual capacity. The magnetoelectric effect can be very strong, for instance the change of electric polarization reaches $100$ $\mu C/m^{2}$ at a constant magnetic field of only $1.5$ Tesla in the case of $100$ $\div$ $10$ nanometer structures which tightly fill the space, composing a metamaterial. The effect does not require using exotic compounds. Based on the obtained results we suggest a number of recommendations for future experimental design.

A principal axis formulation for nonlinear magnetoelastic deformations: Isotropic bodies

In this work a new set of principal axis invariants is proposed in order to study the problem of considering large magneto-elastic deformations, for bodies that are isotropic in the un-deformed configuration when no external magnetic induction is applied. The new set of invariants has clear physical meanings and may have an experimental advantage over the standard invariants used in many previous works in this area. The principal axis invariant formulation is also shown to be more general. Some simple boundary value problems are solved, such as the simple shear, and the biaxial extension of a slab, where with the use of these new invariants, it is possible to study in a much simpler manner the effect of different types of deformations on the response of the material. An illustrated simple specific constitutive equation is proposed which compares well with experiment. • A new set of invariants are proposed to be used in the modelling of magneto-active elastomers. • The new set of invariants has clearer physical meanings than the standard set of Rivlin and Spencer. • Some simple boundary value problems are solved considering the new formulation. • A general form for the total energy function has been proposed.

The study of ultrafast magnetization dynamics induced by femtosecond laser pulses in GdFeCo amorphous film

The time-resolved magneto-optical Kerr spectroscopy technique is used to study the ultrafast magnetization dynamics induced by femtosecond laser pulses in GdFeCo amorphous film. We study concretely the influence of the different pump fluence and the different external magnetic field on magnetization dynamics of ultrafast demagnetization, magnetization reversal and magnetization recovery. The pump fluence dependence magnetization dynamics shows that the degree of demagnetization, the degree of magnetization reversal and the time of magnetization recovery increase with pump fluence, which can be interpreted by the “three-temperature” model. The external magnetic field dependence magnetization dynamics shows that the rate of magnetization reversal increases with the external field, which accord with the magnetization reversal mechanism based on the reversed magnetic domain nucleation and domain-wall motion.

High-gradient ferromagnetic matrices for purification of wastewaters by the method of magnitoelectrolysis

The paper has investigated the efficiency of high-gradient ferromagnetic matrices of a magnetic filter obtained by the method of magnetoelectrolysis at different parameters of the process using a magnetically controlled biosorbent based on the yeast S. cerevisiae and nanomagnetite. The paper has studied the morphology of matrices at different parameters of electric precipitation such as the value of the external magnetic field and magnetization conditions of the matrix base. We have measured quantitative indices of the operation of every type of matrices: maximum efficiency of extraction of the magnetically controlled biosorbent of ions of metals from wastewaters and the optimal time of the operation of manufactured matrices.

Maximum allowable currents in YBa2Cu3O7 superconducting tapes as a function of the coating thickness, external magnetic field induction, and cooling conditions

Maximum allowable (ultimate) currents stably passing through an YBa2Cu3O7 superconducting current-carrying element are determined as a function of a silver (or copper) coating thickness, external magnetic field induction, and cooling conditions. It is found that if a magnetic system based on yttrium ceramics is cooled by a cryogenic coolant, currents causing instabilities (instability onset currents) are almost independent of the coating thickness. If, however, liquid helium is used as a cooling agent, the ultimate current monotonically grows with the thickness of the stabilizing copper coating. It is shown that depending on cooling conditions, the stable values of the current and electric field strength preceding the occurrence of instability may be both higher and lower than the a priori chosen critical parameters of the superconductor. These features should be taken into account in selecting the stable value of the operating current of YBa2Cu3O7 superconducting windings.

Evidence for a Magnetic Seebeck Effect

The irreversible thermodynamics of a continuous medium with magnetic dipoles predicts that a temperature gradient in the presence of magnetization waves induces a magnetic induction field, which is the magnetic analog of the Seebeck effect. This thermal gradient modulates the precession and relaxation. The magnetic Seebeck effect implies that magnetization waves propagating in the direction of the temperature gradient and the external magnetic induction field are less attenuated, while magnetization waves propagating in the opposite direction are more attenuated.

Dynamics studies of cathode spots in a vacuum-arc discharge with ring electrodes

The effect of an external pulse magnetic field with axial and radial components on electric characteristics of the discharge and the configuration of cathode spots of a vacuum arc discharge with ring electrodes is studied experimentally. For arc currents within the range of 0.05–2 kA, shots of the cathode spots at different instants of time are obtained. The dependences of the number of the spots on the discharge current and the mean current per spot are determined. It was found that the expansion rate of the cathode spots area depends significantly on the instant value of the discharge current. It is shown that, when the pulse magnetic field is applied, the discharge voltage increases and the discharge current and number of the cathode spots decreases. It was found that the current interruption is a probability process. The probabilities of the current interruption depending on the maximal value of the external pulse magnetic field induction are determined.

Biodegradation of Magnetic Nanoparticles in Mouse Liver From Combined Analysis of Mössbauer and Magnetization Data

The potential of Mossbauer spectroscopy to study the biodegradation process of magnetic nanoparticles in vivo was demonstrated. Magnetic nanoparticles in form of ferrofluid were administrated to mice. The Mossbauer study of the mice liver samples has shown that in addition to the sextet of lines related to the injected nanoparticles there appears an intense doublet of lines in the spectra with increasing times after the particles administration. Further analysis showed that the doublet consists of two components related to the formation of iron-containing proteins and superparamagnetic behavior of the injected nanoparticles. Using combined analysis of three Mossbauer spectra taken at different external conditions and magnetization curves measured for each sample these components were separated and the evolution with time of each component was characterized.

Simulation of Magnetization Reversal and Domain-Wall Trapping in Submicron Permalloy Wires With Different Wire Geometries

Nonvolatile data storage in today's computers is based on magnetic materials. Hard disk drives (HDD) feature ferromagnetic thin films for recording bits as regions with different magnetizations in the film. At present, the efforts of decreasing HDD size while increasing storage capacity, however, face fundamental limits, namely, the so-called superparamagnetic effect. Research into new generations of magnetic data-storage devices, amongst others, considers as its basic working principle current-induced magnetic domain-wall motion (CIDWM) in magnetic nanowires. In this paper, we present simulation studies of external magnetic field-induced magnetization reversal and domain-wall motion in nanowires of various sizes and shapes. Our results contribute to the basic design principles applied to magnetic structures used in CIDWM experiments. Parameters, such as wire thickness and wire-pad geometries are investigated, and important threshold magnetic field values are presented. In addition, we introduce a novel method of domain-wall trapping in a magnetic wire using the fringe fields of close-by magnets.

Properties and order-disorder competition of spin-1/2 XY model in the ferrimagnetic diamond chain

The elementary excitation spectra of the one-dimensional spin-1/2 XY model in the ferrimagnetic diamond chain at low temperature are calculated by using invariant eigenvector in this paper. And the elementary excitation energies in different cases are discussed. Therefore, analytic solutions of the three critical magnetic field intensities HC1, HC2 and Hpeak in the system are given. It is found that the analytic solutions of three critical magnetic field intensities are correct from the law of the magnetization changing with temperature under different external magnetic fields, and it is explained by the contributions of the three elementary excitations to the magnetization. The external magnetic field dependent magnetization presents a 1/3 magnetized plateau at low temperature. The variation of magnetic susceptibility either with temperature or with external magnetic field shows a double peak structure, this phenomenon indicates that the double peak structure originates from the competition among the ferromagnetic exchange interaction energy of intramolecular electronic spin parallel arrangement in dimer, the antiferromagnetic exchange interaction energy of intermolecular electronic spin antiparallel arrangement in dimer-monomer, the thermal disorder energy and the spin magnetic moment potential energy related to external magnetic field.

The twice ferromagnetic resonance in hexagonal ferrite single rod and paired rods

The microwave electromagnetic properties of Co2-Y hexagonal ferrite single rod and paired rods are demonstrated using a standard waveguide method. With the sweeping of the bias magnetic field, the ferromagnetic resonance occurs twice in the transmission spectra of single ferrite rod, which are induced by the self-bias magnetization and the external field magnetization, respectively. The zero/low-field resonance is determined by the shape anisotropy mainly, and disappears as the rodʼs aspect ratio is relatively low. For the paired rods, when the interval between two parallel rods is small, the zero/low-field resonance vanishes due to the dipolar interaction between two rods.

Spectroscopic Studies of Low-Current (Single-Spot) Short Vacuum Arcs in Axial Magnetic Field

Measurements of radiation intensity spatial distribution for different copper ionization states (CuI, CuII, and CuIII) were carried out in short (8 and 4 mm long) low-current vacuum arcs with copper electrodes. The arc current was I = 60 A = I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> [where I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> is the mean current per cathode spot (CS)]. That is, the single-spot arcs were investigated. The spatial and temporal resolutions were 0.5 mm and 50 μs, respectively. The external axial magnetic field induction was 0 ≤ B ≤ 0.1 T . The studies have shown that the plasma state and the column shape and structure in short arcs are determined not only by cathode processes. In the near-anode region of the arc, changes take place both inside the arc channel and in the “coat” of weakly ionized plasma that surrounds it. The interaction of the high-speed ions of the CS plasma jet (PJ) with the anode forms a flow of atoms from the anode surface part to which the arc is attached. The atoms are ionized in the immediate vicinity of its surface. This increases the plasma concentration and decreases the average charge of ions in the near-anode part of the arc, as compared with the average charge of the CS PJ.

Effects of electric field and magnetic induction on spin injection into organic semiconductors

Spin-polarized injection and transport into ferromagnetic/organic semiconductor structure are studied theoretically in the presence of the external electric field and magnetic induction. Based on the spin-drift–diffusion theory and Ohm's law, we obtain the charge current polarization, which takes into account the special carriers of organic semiconductors. From the calculation, it is found that the current spin polarization is enhanced by several orders of magnitude by tuning the magnetic induction and electric fields. To get an apparent current spin polarization, the effects of spin-depended interfacial resistances and the special carriers in the organic semiconductor, which are polarons and bipolarons, are also discussed.

Magnetometric evaluation of toxicities of chemicals to the lungs and cells

Because the lungs are exposed to airborne hazardous materials, alveolar macrophages (AMs) play a major role in defending against the exposure to various noxious chemical substances. In this study, we reviewed magnetometric investigations of the effects of various chemicals on the lungs and AMs. Magnetometry, using magnetite as an indicator, was used to evaluate the effects of certain chemicals on the lung and AMs. A rapid decrease of the remanent magnetic field after the cessation of external magnetization, a phenomenon called relaxation, was impaired when the lungs and macrophages were exposed to toxic substances. The delayed in vivo relaxation observed in the lungs exposed to magnetite and gallium arsenide was almost identical to the in vitro relaxation observed in the AMs exposed to the same materials. Delayed relaxation was observed in the AMs exposed to silica dust; various fibers, such as chrysotile and some man-made mineral fibers; and toxic arsenic and cadmium compounds. The extracellular release of lactate dehydrogenase activity was found in the AMs exposed to the chemicals. Relaxation is attributed to the cytoskeleton-driven rotation of phagosomes containing magnetite. While the exact mechanism of delayed relaxation due to exposure to harmful chemicals remains to be clarified, cell magnetometry appears to be useful for the safety screening of chemical substances.

Magnetic field assisted fluidization – a unified approach. Part 8. Mass transfer: magnetically assisted bioprocesses

3. Magnetically assisted free-cell bioreactors 3.1. Basic concept and overview of magnetic effects on living cultures 3.2. Reactors with entirely magnetically assisted working volumes 3.2.1. Magnetically assisted activated sludge processes 3.2.2. Magnetically assisted Saccharomyces cerevisiae growth 3.2.2.1. Proliferation of yeast in response to magnetic field application 3.2.2.2. Comments on the proliferation studies: microlevel dynamo concept 3.2.2.3. Fermentation processes 3.2.3. Spirulina behavior under magnetic fields 3.2.4. Magnetotactic bacteria (Magnetospirillum magneticum) 3.2.5. Escherichia coli behavior under magnetic field 3.2.5.1. Static and high-intensity field exposures 3.2.5.2. Low-intensity, time-varying field exposures 3.2.5.3. Brief comments on the magnetic field exposures of E. coli 3.2.6. Other processes exposed to magnetic fields 3.2.6.1. Static magnetic field effects on yeast and bacteria 3.2.6.2. Time-varying magnetic field effects on yeast and bacteria 3.2.6.3. Time-varying magnetic field effects on enzyme activity 3.3. Reactors with recirculation and external culture magnetization 3.3.1. Forced circulation loop of a batch submerged fermentation process 3.3.2. External-loop airlift with magnetization 3.3.3. Comments on the bioreactors with external loops and intermittent magnetizations 3.4. Comments on free-cell magnetically assisted bioreactors

Analysis of an MMI-Based Six-Port Circulator by Using 3-D Magneto-Optical Beam Propagation Method

An MMI-based six-port circulator is analyzed by 3-D magneto-optical (MO) beam propagation method (BPM). Since opposite nonreciprocal 4pi/3-phase shifts are introduced into the two sided interferometric arms of 3 times 3 mirror-image MMI coupler, light travels through this device in a nonreciprocal fashion and obeys the sequential order. After using the Ce:YIG/SOI bonding waveguide to construct the proposed circulator, the 3-D MO BPM formula are validated for the first time to simulate nonreciprocal device with external magnetization perpendicular to the light propagation direction. Simulation shows that this device features in easy fabrication, good operation bandwidth, ability to reduce the port count number.

Polarized neutron reflectometry from the interface of the heterostructures SiO2(Co)/Si and SiO2(Co)/GaAs

Polarized neutron reflectometry is used to investigate SiO 2 (Co) granular films (70 at% of Co nanoparticles in SiO 2 matrix) deposited on Si and GaAs substrates. The aim of the study is to compare magnetization depth profiles in two systems: in SiO 2 (Co)/GaAs heterostructure which shows at room temperature giant injection magnetoresistance (IMR) with the system SiO 2 (Co)/Si which reveals almost no IMR effect. We found that at room temperature and at the same value of external magnetic field mean magnetization in the SiO 2 (Co)/GaAs sample is much higher than in the case of SiO 2 (Co)/Si. We also demonstrate that magnetic scattering length density, and hence, magnetization profile strongly depends on the substrate. We show that SiO 2 (Co)/Si heterostructure is ferromagnetically ordered within the temperature range between 120 and 460 K what could explain a weak IMR.

Magnetic measurements of superconductingNdFeAsO0.82F0.18 oxypnictide

By means of magnetic measurements we have studied the magnetic properties of theNdFeAsO0.82F0.18 superconductor. We estimated the upper critical fieldHc2ab(T) from the temperature at which the inverse magnetization deviates from linear behavior.Low field magnetic measurements revealed that a external magnetic induction ofB = 0.01 T destroys the superconducting path between grains (weak-link behavior). Nd ions behaveas isolated paramagnetic centers. This is evident since for magnetic inductions larger than0.5 T a paramagnetic moment arises from the Nd that overcomes the superconductingdiamagnetic signal. Hysteresis loops at several temperatures revealed that thecritical current falls rapidly with temperature. The temperature variationof the reversible magnetization shows a behavior that is reminiscent of high-Tc cuprates, indicating the important role of thermal fluctuations.