External Magnetic Field In Order Research Articles

The Effect of Arrive Angle of External Magnetic Field on The Shape of Hysteresis Curve Permalloy Ni80Fe20 By Simulation

Magnetic sensor is a type of sensor that utilizes changes in resistance caused by changes in the magnetic field H or B. One of the suitable magnetic materials to be used as a study material for making magnetic sensors is permalloy Ni80Fe20. The reading error of the magnetic sensor of the Ni80Fe20 permalloy material affects hysteresis curve of the material and requires correction of the angle of incidence of the external magnetic field in order to provide accurate results on the storage media. In this our current research using Finite Difference OOMMF, we investigated the effect of the angle of incidence of the external magnetic field (H) on the hysteresis curve was carried out on an application based on. The research was conducted by reviewing the parameter literature of the Ni80Fe20 permalloy material and then compiling it in a script and simulating it on an application based on Finite Difference OOMMF. The data obtained from the simulation are normalized magnetization (m), external magnetic field H and coercivity field (Hc) which have been influenced by the angle of incidence. The results of the hysteresis curve at a size of 5 nm with a variation of the angle of incidence 0o are indicated by the value of the external magnetic field H of 10000 mT to -10000 mT with a coercive field Hc of 5000 mT to -5000 mT. The normalized magnetization value m is 1 to -1. The variation of the angle of incidence of 30o produces a coercive field Hc of -108.3 mT to 108.3 mT and a normalized magnetization of 0.86 to -0.86. The 45o incident angle variation produces a coercive field Hc -88.4 mT to 88.4 mT and a normalized magnetization of -0.7 to 0.7

ЭЛЕКТРОМАГНИТНЫЙ СПОСОБ ЧАСТОТНОГО АНАЛИЗА ПОПЕРЕЧНЫХ КОЛЕБАНИЙ СТЕРЖНЯ

Vibration-based diagnostics of constructions is an obligatory technical procedure in mechanical engineering. In this regard, there is a problem of an adequate theoretical description of vibration processes in various structures with account for end fixity conditions, as well as the creation of experimental facilities for non-contact testing. The paper presents a theoretical basis and experimental verification results for a method of electromagnetic frequency analysis of rod systems. The essence of the method is the experimental determination of natural oscillation frequencies and their comparison with reference values. The main attention is paid to a theoretical description of transverse vibrations of a cantilever conductive rod in an external magnetic field in order to determine reference frequencies of a defect-free sample. The presence of the external magnetic field gives rise to the distributed electromagnetic force exerted on the rod. In the case of natural oscillations, the magnetic force is damping, which leads to a change in damping factors of partial oscillations. The electromagnetic effect is selective towards vibrational modes; hence, the damping factors of various partial oscillations of the rod vary to different degrees. This fact allows one to determine an optimal location of the area with acting magnetic field, as well as its width when measuring a given frequency of sample testing. The proposed method has several advantages: indestructibility of the sample, non-contact measurements, invariability of mechanical properties of the sample during the tests.

Determination of the terahertz pulse emitting dipole orientation by terahertz emission measurements

Terahertz pulse emission from the photoexcited semiconductor surface heavily depends on the orientation of the photo-induced electric dipole. Two methods to determine the orientation of the terahertz pulse emitting dipole have been demonstrated. Method I relies on the measurement of THz emission dependencies on the angle of incidence in the transmission geometry, while method II is based on the measurements of THz emission in the reflection geometry. Theoretical reasoning for both of these methods has been presented. Both of these methods have been tested with a semi-insulating GaAs substrate using an external magnetic field in order to change the tilt angle of the electric dipole. The investigation presented in this work leads to an assumption that the magnetic field induced change in the dipole tilt angle is proportional to the mobility of electrons. Thus, the suggested method may become a promising tool for testing the quality of substrates and epitaxial layers.

A microscopic approach to heating rate of ferrofluid droplets by a magnetic field

In this work, we study the heating process of colloidal ferrofluids by a magnetic field. The heating of the fluid occurs by the magnetic relaxation of the nanoparticles which provide thermal energy for the host liquid. In the limit of small volumes, the relaxation process occurs through the Néel mechanism since the magnetic nanoparticles present superparamagnetic behavior. Within this limit, we have used a microscopic model for the coupling to phonons and external magnetic field in order to model the relaxation mechanism and to obtain an expression for the heating rate of the fluid as a function of microscopic parameters. The analysis allows determining appropriate conditions for an optimal heating rate for ferrofluids based on superparamagnetic nanoparticles.

From Kinetic Instability to Bose-Einstein Condensation and Magnon Supercurrents.

Evolution of an overpopulated gas of magnons to a Bose-Einstein condensate and excitation of a magnon supercurrent, propelled by a phase gradient in the condensate wave function, can be observed at room temperature by means of the Brillouin light scattering spectroscopy in an yttrium iron garnet material. We study these phenomena in a wide range of external magnetic fields in order to understand their properties when externally pumped magnons are transferred towards the condensed state via two distinct channels: a multistage Kolmogorov-Zakharov cascade of the weak-wave turbulence or a one-step kinetic instability process. Our main result is that opening the kinetic instability channel leads to the formation of a much denser magnon condensate and to a stronger magnon supercurrent compared to the cascade mechanism alone.

Enhanced electrical conductivity of collagen films through long-range aligned iron oxide nanoparticles

The development of biocompatible collagen substrates able to conduct electric current along specific pathways represent an appealing issue in tissue engineering, since it is well known that electrical stimuli significantly affects important cell behaviour, such as proliferation, differentiation, directional migration, and, therefore, tissue regeneration. In this work, a cheap and easy approach was proposed to produce collagen-based films exhibiting enhanced electrical conductivity, through the simple manipulation of a weak external magnetic trigger. Paramagnetic iron oxide nanoparticles (NPs) capped by a biocompatible polyethylene-glycol coating were synthetized by a co-precipitation and solvothermic method and sprayed onto a collagen suspension. The system was then subjected to a static external magnetic field in order to conveniently tune NPs organization. Under the action of the external stimulus, NPs were induced to orient along the magnetic field lines, forming long-range aligned micropatterns within the collagen matrix. Drying of the substrate following water evaporation permanently blocked the magnetic architecture produced, thereby preserving NPs organization even after magnetic field removal. Electrical conductivity measurements clearly showed that the presence of such a magnetic framework endowed collagen with marked conductive properties in specific directions. The biocompatibility of the paramagnetic collagen films was also demonstrated by MTT cell cytotoxicity test.

The enhanced MR performance of dimorphic MR suspensions containing either magnetic rods or their non-magnetic analogs

A co-precipitation method was used to prepare non-magnetic rod-like ferrous oxalate dihydrate (Fe2CO4 · 2H2O) particles that were further turned into iron oxide (Fe3O4) magnetic rod-like particles. A simple precursor-assisted thermal decomposition technique enabled the preservation of the morphology and size of the precursor ferrous oxalate dihydrate particles, thus allowing their magnetic analogs to be obtained. Both types of rod-like particles were used as an additive together with spherical carbonyl iron (CI) particles in novel dimorphic magnetorheological (MR) suspensions. Controlled shear rate mode experiments were performed using a rotational rheometer with a source of an external magnetic field in order to investigate their MR behavior. Moreover, the properties of the novel prepared dimorphic MR (DMR) suspensions were compared with conventional MR suspensions based on spherical CI microparticles. It was found that the DMR suspensions exhibit enhanced MR performance as well as enhanced sedimentation stability in comparison with the MR suspension based on pure CI. The dimorphic suspensions containing magnetic rod-like additives further exhibited significant MR hardening at low shear rates. The properties of CI-based suspensions can be thus optimized by using various additive substances.

The magnetic introduction of magnetite nanoparticles into live cells for radiosensibility enhancement

Earlier we proposed a new radiotherapy enhancement method that entails the administration of 57Fe iron-oxide nanoparticles into the cells [5]. Within this work we were prompt to investigate the capability of iron oxide nanoparticles with monolayer coating to penetrate into live cells. Magnetite particle samples were synthesized and stabilized with HCl or citric acid. The cells were incubated in the presence of nanoparticles for 1h, washed and dried. To distinguish inside-cell particles from outside ones a set of experiments with low temperature incubation was carried out. Several cell samples were prepared in the presence of an external magnetic field in order to study the possibility of the nanoparticle uptake enhancement. To evaluate the amount of particles in each cell sample we used a SQUID-magnetometer. The nanoparticle suspension with HCl stabilization turned to be inadequate for intracellular introduction. Approximately 2·105 particles with citric acid covering conjugated with each cell after incubation at normal conditions. An application of an external magnetic field increased this amount up to 107 particles/cell. Most probably much of these particles penetrated into cells.

Controlling the Goos-Hänchen shift with external electric and magnetic fields in an electro-optic/magneto-electric heterostructure

We present a theoretical investigation of the Goos-Hänchen effect upon light reflection from a heterostructure consisting of an electro-optic film deposited on a magneto-electric film grown on a nonmagnetic dielectric substrate. It is shown that the linear magneto-electric interaction leads to an increase of the lateral shift even in the absence of any applied electric field. The presence of the electro-optic layer enables the control of the Goos-Hänchen shift and of the position of its maximum (with respect to the angle of incidence) through a variation of the magnitude and orientation of an applied electric field. It is also demonstrated that applying an external magnetic field in order to reverse the magnetization in the magnetic layer results (under the influence of the magneto-electric interaction in the system) in a sign reversal of the lateral shift but a nonreciprocal change of its amplitude.

Injectable, magnetoresponsive hydrogels for in situ physical actuation of osteochondral tissue regeneration

Event Abstract Back to Event Injectable, magnetoresponsive hydrogels for in situ physical actuation of osteochondral tissue regeneration Adedokun Adedoyin1 and Adam K. Ekenseair1 1 Northeastern University, Chemical Engineering, United States Introduction: Every year 3.1 million surgeries are performed to treat bone and cartilage damage caused by Osteoarthritis (OA), however, many of these procedures fail to restore full functionality and structure[1]. In particular, articular cartilage has proven challenging to heal due to its avascular and heterogeneous structure. Recent efforts have sought to move away from implantable scaffolds and develop novel, minimally invasive therapies capable of forming in situ and promoting close contact with existing tissue to enhance tissue repair. In particular, thermogelling macromers (TGM) that have a lower critical solution temperature (LCST) close to body temperature, such as poly(N-isopropylacrylamide) (PNiPAAm), are promising candidates capable of delivering viable encapsulated cells[2]. The next grand challenge in the development of injectable scaffolds is to create responsive materials that can be externally directed in a spatiotemporal manner to guide the regeneration of a heterogeneous tissue defect. This paper reports on the development of injectable, dual-gelling bionanocomposite hydrogels composed of PNiPAAm-based TGMs, degradable polyamidoamine (PAMAM) crosslinkers, and functional iron oxide (Fe3O4) nanoparticles capable of responding to an external magnetic field in order to stimulate cell activity and control the regenerative process in situ. Materials and Methods: PNiPAAm was copolymerized with glycidyl methacrylate (GMA) and PAMAM crosslinkers were created from piperazine and methylene bisacrylamide following previous synthesis procedures[3]. 50 nm and 500 nm amine-functionalized Fe3O4 particles were purchased from Ocean Nanotech, LLC. Injectable solutions were mixed and injected into a Teflon mold at 37ºC to form magnetic hydrogels. Polymer molecular weight was determined by GPC; LCST by differential scanning calorimetry (DSC); and Young’s Modulus by rheology. The magnetic properties of the hydrogel were determined by SQUID and tangential force measurements. The viability, activity and differentiation of mesenchymal stem cells were evaluated in vitro under varied magnetically-actuated stimulation regimes. Results and Discussion: The incorporation of nanoparticles into the injectable hydrogel system did not alter the LCST or thermogelation process. SQUID analysis demonstrated that the nanocomposite hydrogels exhibit paramagnetic behavior under strong magnetic fields, and tangential force measurements were made to evaluate the efficacy of utilizing an externally-controlled magnetic field to mechanically stimulate encapsulated cells (Fig, 1 & 2). Finally, the in situ delivery of viable cell populations encapsulated in the bionanocomposite hydrogel was demonstrated (Fig. 2 inset), and the effects of magnetic stimulation were elucidated. Conclusions: An injectable, bionanocomposite hydrogel scaffold responsive to an external magnetic field was developed and demonstrated potential for guided regeneration of osteochondral tissue defects. Robert Egan at Northeastern University; Dr. Abigail Koppes at Northeastern University; Dr. Sridhar at Northeastern University; Northeastern University's Tier 1 Grant Program; Chemical Engineering Department Northeastern University

An adapted Coffey model for studying susceptibility losses in interacting magnetic nanoparticles

Background: Nanoparticles can be used in biomedical applications, such as contrast agents for magnetic resonance imaging, in tumor therapy or against cardiovascular diseases. Single-domain nanoparticles dissipate heat through susceptibility losses in two modes: Néel relaxation and Brownian relaxation.Results: Since a consistent theory for the Néel relaxation time that is applicable to systems of interacting nanoparticles has not yet been developed, we adapted the Coffey theoretical model for the Néel relaxation time in external magnetic fields in order to consider local dipolar magnetic fields. Then, we obtained the effective relaxation time. The effective relaxation time is further used for obtaining values of specific loss power (SLP) through linear response theory (LRT). A comparative analysis between our model and the discrete orientation model, more often used in literature, and a comparison with experimental data from literature have been carried out, in order to choose the optimal magnetic parameters of a nanoparticle system.Conclusion: In this way, we can study effects of the nanoparticle concentration on SLP in an acceptable range of frequencies and amplitudes of external magnetic fields for biomedical applications, especially for tumor therapy by magnetic hyperthermia.

Structural and magnetic properties of iron nanowires and iron nanoparticles fabricated through a reduction reaction.

The main goal of this work is to study the structural and magnetic properties of iron nanowires and iron nanoparticles, which have been fabricated in almost the same processes. The only difference in the synthesis is an application of an external magnetic field in order to form the iron nanowires. Both nanomaterials have been examined by means of transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray diffractometry and Mössbauer spectrometry to determine their structures. Structural investigations confirm that obtained iron nanowires as well as nanoparticles reveal core–shell structures and they are composed of crystalline iron cores that are covered by amorphous or highly defected phases of iron and iron oxides. Magnetic properties have been measured using a vibrating sample magnetometer. The obtained values of coercivity, remanent magnetization, saturation magnetization as well as Curie temperature differ for both studied nanostructures. Higher values of magnetizations are observed for iron nanowires. At the same time, coercivity and Curie temperature are higher for iron nanoparticles.

Instrument for in-situ orientation of superconducting thin-film resonators used for electron-spin resonance experiments

When used in electron-spin resonance measurements, superconducting thin-film resonators must be precisely oriented relative to the external magnetic field in order to prevent the trapping of magnetic flux and the associated degradation of resonator performance. We present a compact design solution for this problem that allows in-situ control of the orientation of the resonator at cryogenic temperatures. Tests of the apparatus show that when proper alignment is achieved, there is almost no hysteresis in the field dependence of the resonant frequency.

Particle modelling of low-pressure radio-frequency magnetron discharges including the effects of self-induced electromagnetic fields

Modelling of radio-frequency (RF) magnetron discharges is performed using a particle-in-cell/Monte Carlo technique in the case of low-pressure argon gas at 4 mTorr and high external magnetic field in order to self-maintain the discharge and to generate an energetic quasi-ion beam required for cathode sputtering applications. An emphasis is made, for the first time in the literature in the case of low-pressure RF discharges, on the development of a particle model coupled with the full set of electromagnetic field equations. The aim is to analyse the effect on the RF plasma features of the plasma-induced magnetic field resulting from the coupling of the Maxwell–Ampere equation. We also analysed the effect of the electric field due to the time variation of magnetic field resulting from the coupling of the Maxwell–Faraday equation. For the present asymmetrical plasma reactor, the mean relative difference on, for instance, the ion density with and without the consideration of plasma-induced magnetic and electric fields due to the time variation of the magnetic field can reach about 2.5% in the region of the plasma bulk and about 10% in the lateral sheath. The effects of these two induced electromagnetic fields are in fact higher in the regions where the radial magnetic field generated by the external magnets belonging to the magnetron configuration is low. These non-negligible relative differences clearly show the importance of rigorously taking into account, beyond the usual Poisson's equation for the space charge electric field, the full set of electromagnetic Maxwell equations for a more accurate modelling of these low-pressure discharges, particularly when the total current density reaches a few mA cm−2.

Investigation of selective realignment of the preferred magnetic direction in spin-valve layer stacks using laser radiation

Selective realignment of the preferred magnetization direction in a laser micro structured GMR spin-valve layer system (Ni81Fe19/Co90Fe10/Cu/Co90Fe10/IrMn/Ni81Fe19) with a total film thickness of 23nm was studied. For this, patterns of isolated microstructures (500μm×200μm) were fabricated by laser ablation. These micropatterns were annealed using laser irradiation at a temperature above the IrMn Néel temperature. During laser annealing, the sample was subjected to an external magnetic field in order to selectively realign the magnetic direction of the reference layer. Two different laser assisted annealing techniques were investigated applying either continuous or pulsed laser systems. After laser annealing, the magnetic properties of the micropatterns were investigated using a magnetic microsensor and magneto optical Kerr effect set up.

Paramagnetic epoxy-functionalized mesostructured cellular foams with an open pore system for immobilization of penicillin G acylase

Paramagnetic epoxy-functionalized mesostructured cellular foams (PEMCFs), prepared by reacting the epoxy groups grafted on the outer surface of epoxy-functionalized MCFs with the amino groups of l-cysteine modified on the surface of Fe3O4 nanoparticles, were characterized by SAXS, powder XRD, nitrogen sorption, TEM, FT-IR, TG, ICP-AES and magnetic susceptibility measurements, and investigated as the support for immobilization of penicillin G acylase (PGA). The results show that paramagnetic Fe3O4 nanoparticles were successfully grafted covalently on the outer surface of PEMCFs due to the larger particle size of Fe3O4 nanoparticles, and PGA was successfully immobilized covalently on the inner surface of PEMCFs. PGA immobilized on PEMCFs shows the highest initial activity and operational stability among those ever reported in the literatures, which had the initial activity of 8800Ug−1 and retained 94.5% of its initial activity after recycled for 10 times. PGA immobilized on PEMCFs can be easily recycled by the aid of an external magnetic field in order to replace the tedious separation of high-speed centrifugation.

A novel electron gun for inline MRI‐linac configurations

This work introduces a new electron gun geometry capable of robust functioning in the presence of a high strength external magnetic field for axisymmetric magnetic resonance imaging (MRI)-linac configurations. This allows an inline MRI-linac to operate without the need to isolate the linear accelerator (linac) using a magnetic shield. This MRI-linac integration approach not only leaves the magnet homogeneity unchanged but also provides the linac flexibility to move along the magnet axis of symmetry if the source to target distance needs to be adjusted. Simple electron gun geometry modifications of a Varian 600 C electron gun are considered and solved in the presence of an external magnetic field in order to determine a set of design principles for the new geometry. Based on these results, a new gun geometry is proposed and optimized in the fringe field of a 0.5 T open bore MRI magnet (GE Signa SP). A computer model for the 6 MeV Varian 600 C linac is used to determine the capture efficiency of the new electron gun-linac system in the presence of the fringe field of the same MRI scanner. The behavior of the new electron gun plus the linac system is also studied in the fringe fields of two other magnets, a 1.0 T prototype open bore magnet and a 1.5 T GE Conquest scanner. Simple geometrical modifications of the original electron gun geometry do not provide feasible solutions. However, these tests show that a smaller transverse cathode diameter with a flat surface and a slightly larger anode diameter could alleviate the current loss due to beam interactions with the anode in the presence of magnetic fields. Based on these findings, an initial geometry resembling a parallel plate capacitor with a hole in the anode is proposed. The optimization procedure finds a cathode-anode distance of 5 mm, a focusing electrode angle of 5°, and an anode drift tube length of 17.1 mm. Also, the linac can be displaced with ± 15 cm along the axis of the 0.5 T magnet without capture efficiency reduction below the experimental value in zero field. In this range of linac displacements, the electron beam generated by the new gun geometry is more effectively injected into the linac in the presence of an external magnetic field, resulting in approximately 20% increase of the target current compared to the original gun geometry behavior at zero field. The new gun geometry can generate and accelerate electron beams in external magnetic fields without current loss for fields higher than 0.11 T. The new electron-gun geometry is robust enough to function in the fringe fields of the other two magnets with a target current loss of no more than 16% with respect to the current obtained with no external magnetic fields. In this work, a specially designed electron gun was presented which can operate in the presence of axisymmetric strong magnetic fringe fields of MRI magnets. Computer simulations show that the electron gun can produce high quality beams which can be injected into a straight through linac such as Varian 600 C and accelerated with more efficiency in the presence of the external magnetic fields. Also, the new configuration allows linac displacements along the magnet axis in a range equal to the diameter of the imaging spherical volume of the magnet under consideration. The new electron gun-linac system can function in the fringe field of a MRI magnet if the field strength at the cathode position is higher than 0.11 T. The capture efficiency of the linac depends on the magnetic field strength and the field gradient. The higher the gradient the better the capture efficiency. The capture efficiency does not degrade more than 16%.

Electronic Theory of Ultrafast Spin Dynamics in NiO

Electronic Theory of Ultrafast Spin Dynamics in NiO NiO is a good candidate for ultrafast magnetic switching because of its large spin density, antiferromagnetic order, and clearly separated intragap states. In order to detect and monitor the switching dynamics, we develop a systematic approach to study optical second harmonic generation (SHG) in NiO, both at the (001) surface and in the bulk. In our calculations NiO is modeled as a doubly embedded cluster. All intragap d-states of the bulk and the (001) surface are obtained with highly-correlational quantum chemistry and propagated in time under the influence of a static magnetic field and a laser pulse. We find that demagnetization and switching can be best achieved in a subpicosecond regime with linearly rather than circularly polarized light. We also show the importance of including an external magnetic field in order to distinguish spin-up and spin-down states and the necessity of including magnetic-dipole transitions in order to realize the process in the centrosymmetric bulk. Having already shown the effects of phonons in the SHG for the bulk NiO within the frozen-phonon approximation, and following the same trail of thoughts, we discuss the role of phonons in a fully quantized picture as a symmetrylowering mechanism in the switching scenario and investigate the electronic and lattice temperature effects.

Extension of the frequency range of Josephson impedance spectroscopy

The results of the spectral analysis of a high-temperature superconducting (HTSC) log-periodic antenna integrated with a HTSC Josephson junction (JJ) and operating, in this case, as a test resonant system are presented. Current-voltage characteristics of the JJ and dependences of its differential resistance on the voltage across the JJ are measured at a temperature of 5 K by varying the JJ critical current by an external magnetic field in order to extend the operating frequency range of the spectral analysis. The low-frequency boundary of the spectral analysis, which is determined by temperature fluctuations, is lowered to 64 GHz. The equivalent circuit of an integrated device consisting of the JJ and the log-periodic antenna is analyzed. The real part of the antenna admittance is reconstructed from experimental data in the frequency range 65–1200 GHz. Experimental results are compared with the results of numerical calculation.

Configuration of minimal domains in dipole lattices

Lattices of magnetic dipoles made of a small number of rows (two to four) are studied. Minimal stationary domains that can be formed in the lattices and conditions of their formation are revealed. It is shown that it is sufficient to expose a single dipole to an external magnetic field in order to destroy the domain. Comparative analysis of a change in the magnetic moment of the system accompanying formation and destruction of domains in different lattices is performed.