Intensity Of External Magnetic Field Research Articles

Diamagnetic flux measurement without a compensation coil in the Hanbit mirror

A diamagnetic loop receives the external magnetic field fluctuations distorted by vacuum vessel eddy currents. Without installing a compensation coil in vacuum, the fluctuation is compensated from the circuit model of the vacuum vessel with only a Rogowski coil measurement of the external magnetic coil current. The vacuum vessel is modeled as a mixture of several inductively linked conductors. By solving the circuit equations, it is shown that the distortion is given as a convolution of exponentially decaying functions and the Rogowski coil signal. The characteristic time is obtained by a least-squares fitting algorithm. The convolution is calculated by using the fast Fourier transform technique. The external magnetic field fluctuations of the diamagnetic loop are reduced to 0.005% of the external magnetic field intensity.

Effect of External Magnetic Field on Ultrasonic Propagation Velocity in Magnetic Fluids

Experimental results for the properties of ultrasonic propagation velocity in kerosene-based and water-based magnetic fluids are reported. Ultrasonic wave frequencies of 1 MHz, 2 MHz and 4 MHz are used and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0° to 90°. The ultrasonic propagation velocity in magnetic fluids is dependent on temperature, elapsed time of applying the magnetic field, and magnetic field intensity. Hysteresis and anisotropy of ultrasonic propagation velocity are observed. These interesting results seem to be related to chain-like cluster formation in the magnetic fluids and the characteristic period of Brownian motion of the magnetic particles.

Spatial shape demagnetising factors of disc, equilateral triangle and irregular hexagonal magnetic insulators

The connection between the external and internal direct magnetic field intensities in an ellipsoidal magnetic insulator in a uniform field is a classic result in the literature. It is usually stated in terms of shape demagnetising factors. The case of the non-ellipsoidal geometry in a uniform field has been dealt with in a number of approximate ways but has by and large been restricted to disc geometries in infinite space. The aim of the paper is to verify some existing relationships on the spatial dependent shape demagnetising factors of the classic disc insulator by having recourse to a static magnetic solver. The demagnetising factors along the two main coordinates of equilateral and irregular hexagonal magnetic insulators are also evaluated.

Influence of magnetic field on ultrasonic propagation velocity in magnetic fluids

Experimental results for anisotropy and hysteresis of ultrasonic propagation velocity in a kerosene-based magnetic fluid are reported. The ultrasonic frequencies used are 1, 2 and 4 MHz and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0 ∘ to 90 ∘ . The ultrasonic propagation velocity increases with magnetic field intensity and ultrasonic frequency. Anisotropy due to the configuration of chain-like clusters is also observed. These results seem to be caused by cluster formation and the characteristic time of Brownian motion of the magnetic particles.

The effect of temperature on the anisotropy of ultrasound attenuation in a ferrofluid

This paper reports results of a study on the acoustic properties of a ferrofluid, APG-513A. The anisotropy of the ultrasonic wave absorption coefficient was determined in a sample subjected to an external magnetic field. The measurements were performed in a strong magnetic field HDC = 125 kA m−1, for temperatures of 1–60°C. The dependence of the absorption coefficient of the ultrasonic wave (f = 3.6 MHz) on the angle between the direction of measurement and that of the magnetic field provided important information on the ferrofluid structure in a magnetic field. A comparison of the experimental results with the predictions of the Taketomi theory allowed a determination of the cluster radius and the number density of the colloidal particles. These data allowed us to draw conclusions about the changes in the parameters describing the structure of the ferrofluid at different temperatures. The per cent contribution of the magnetic particles in the cluster structures was estimated. On the basis of the measurements performed, it was possible to establish the proportion of the ultrasonic wave used for excitation of the translational and rotational degrees of freedom. The results revealed a significant effect of temperature on the translational and rotational components of the absorption coefficient. Moreover, the magnetic susceptibility was measured versus the external magnetic field intensity.

Magnetically actuated bi-directional microactuators with permalloy and Fe/Pt hard magnet

Bi-directional polyimide (PI) electromagnetic microactuator with different geometries are designed, fabricated and tested. Fabrication of the electromagnetic microactuator consists of 10μm thick Ni/Fe (80/20) permalloy deposition on the PI diaphragm by electroplating, high aspect ratio electroplating of copper planar coil with 10μm in thickness, bulk micromachining, and excimer laser selective ablation. They were fabricated by a novel concept avoiding the etching selectivity and residual stress problems during wafer etching. A mathematical model is created by ANSYS software to analyze the microactuator. The external magnetic field intensity (Hext) generated by the planar coil is simulated by ANSYS software. ANSYS software is used to predict the deflection angle of the microactuator. Besides, to provide bi-directional and large deflection angle of microactuator, hard magnet Fe/Pt is deposited at a low temperature of 300°C by sputtering onto the PI diaphragm to produce a perpendicular magnetic anisotropic field. This magnetic field can enhance the interaction with Hext to induce attractive and repulsive bi-directional force to provide large displacement. The results of magnetic microactuator with and without hard magnets are compared and discussed. The preliminary result reveals that the electromagnetic microactuator with hard magnet shows a greater deflection angle than that without one.

Microstructure and magnetic properties of Fe–25Cr–12Co–1Si alloy thermo-magnetically treated in intense magnetic field

The Fe–25Cr–12Co–1Si alloy was subjected to thermo-magnetic treatment (TMT) in an intense magnetic field up to 10kOe. Changes of particle size of the ferromagnetic α1 phase were studied by TEM and quantitatively analyzed by the mean linear intercept method. It was found that the appropriate aspect ratio of the particles of the ferromagnetic α1 phase can only be obtained with definitely restrictive TMT parameters. Coarsening of the particles of the ferromagnetic α1 phase during spinodal decomposition was defined by calculation of time component n. Influence of the parameters of TMT, such as intensity of external magnetic field, TMT temperature and holding time, on the magnetic properties of the alloy was investigated separately. The optimal magnetic properties obtained for the Fe–25Cr–12Co–1Si alloy are Br=13.1kG, iHc=614Oe and (BH)max=4.1MGOe. The results obtained enable further understanding of the internal relation between the parameters of TMT and microstructure, as well as the magnetic properties for the Fe–Cr–Co type alloys.

Perpendicular magnetic anisotropic field for polyimide-based microactuator with excimer laser ablation

A novel polyimide-based magnetic microactuator is presented. Two types of magnetic microactuators with different beams in dimension are fabricated, tested and demonstrated. The combination process of thick photoresist lithography, micro-electroplating, bulk micromachining, and excimer laser ablation is performed. Polyimide diaphragm with micro-electroplated Ni/Fe (80/20) permalloy is bulk micromachined firstly, and then polyimide microstructures are ablated by mask projection of 248 nm excimer laser. This new concept demonstrates that polyimide microstructures can be post-ablated after bulk micromachining. To provide large deflection angle of microactuators, hard magnetic Fe/Pt is deposited under low temperature less than 300 °C by sputtering onto the polyimide suspension diaphragm to produce a perpendicular magnetic anisotropic field. This anisotropic field can enhance the interaction with the external magnetic field intensity ( H ext) to induce attractive and repulsive force to provide large displacement. The results of magnetic microactuators with and without hard magnetic are compared and discussed. The preliminary result reveals that the electromagnetic microactuator with hard magnet shows a greater deflection angle than that without one. Besides, ANSYS software was used to simulate the deflection angle of the microactuators. The experimental result shows a good agreement with theoretical simulation.

Perpendicular magnetic anisotropic field for polyimide-based microactuator with excimer laser ablation

A novel polyimide-based magnetic microactuator is presented. Two types of magnetic microactuators with different beams in dimension are fabricated, tested and demonstrated. The combination process of thick photoresist lithography, micro-electroplating, bulk micromachining, and excimer laser ablation is performed. Polyimide diaphragm with micro-electroplated Ni/Fe (80/20) permalloy is bulk micromachined firstly, and then polyimide microstructures are ablated by mask projection of 248 nm excimer laser. This new concept demonstrates that polyimide microstructures can be post-ablated after bulk micromachining. To provide large deflection angle of microactuators, hard magnetic Fe/Pt is deposited under low temperature less than 300 °C by sputtering onto the polyimide suspension diaphragm to produce a perpendicular magnetic anisotropic field. This anisotropic field can enhance the interaction with the external magnetic field intensity ( H ext ) to induce attractive and repulsive force to provide large displacement. The results of magnetic microactuators with and without hard magnetic are compared and discussed. The preliminary result reveals that the electromagnetic microactuator with hard magnet shows a greater deflection angle than that without one. Besides, ANSYS software was used to simulate the deflection angle of the microactuators. The experimental result shows a good agreement with theoretical simulation.

An Investigation of the Optical Characteristics of a Pulse Discharge in Argon at Atmospheric Pressure in an External Magnetic Field

The optical regularities of the development of the plasma channel of a high-pressure pulse discharge are investigated in the presence of high gradients of magnetic field at the plasma–neutral gas interface (∇PH ∼ 109 Pa/m) and a low inductance per unit length of the discharge circuit (L ∼ 10–4 H/m). It is shown that, when the rate of delivery of electric energy into the discharge gap varies and in the presence of intensity of external magnetic field, the dynamics of zones of high conductivity and brightness of glow change significantly. The behavior of the temporal evolution of the distribution of the radiation intensity over the spectrum in the optical range is studied.

Magnetotransport in variable-coupling one-dimensional ballistic constrictions

A scheme to produce closely spaced high-quality one-dimensional electronic channels is presented. It is based on standard nanolithography fabrication applied to a single, wide quantum well AlGaAs/GaAs heterostructure where the spatial separation of the wire modes is given by Coulomb repulsion. The lack of a composition-induced barrier in the double layer leads to electron mobility of 5×106 cm2/Vs in the starting double two-dimensional system. This in turn yields high-quality one-dimensional channels following nanolithography, as shown by our detailed analysis of the magnetotransport properties of the system. Variable coupling is achieved by split-gate polarization and external magnetic-field intensity and orientation. The relevance for the implementation of coherent nanodevices of this fabrication approach is discussed.

Magnetic properties of submicron circular permalloy dots

Both the static and the dynamical magnetic properties of a square array of circular permalloy dots, characterized by a magnetic vortex configuration of the magnetization, have been investigated by means of magneto-optical Kerr effect and Brillouin light scattering (BLS) from thermally excited spin waves. The measured hysteresis loop can be satisfactorily reproduced by micromagnetic simulations, showing that the vortex configuration is stable over a wide range of applied field. The high frequency response of the dots was analyzed by BLS measurements performed under an external magnetic field intensity large enough to uniformly magnetize the dots. Evidence is given of a marked discretization of the spin wave spectrum with respect to the case of the continuous permalloy film, where only one peak, corresponding to the Damon-Eshbach mode, was detected. The experimental frequencies have been compared to those calculated using a recently developed analytical model for a flat uniformly magnetized cylindrical dot.

On diffraction of waves by the infinite grating of circular dielectric cylinders at oblique incidence: Floquet representation

We investigate the diffraction of plane E-polarized electromagnetic waves by an infinite array of infinitely long circular dielectric cylinders for the most generalized case of oblique incidence. Employing the Sommerfeld integral representation of the Hankel function, and exploiting Poisson's summation formula in separation-of-variables solution, we have acquired a new representation for the diffraction of waves by the infinite grating of the circular dielectric cylinders at oblique incidence. The exact solutions for the external electric and magnetic field intensities have been derived in terms of the diffraction angles of the grating which are obtained by solving the grating equation. In addition, the transmitted and reflected fields of the infinite grating have been presented in terms of propagating and evanescent Floquet modes.

The effect of the rate of magnetic field and temperature changes on the ultrasonic wave absorption coefficient in a magnetic fluid

The rate of external magnetic field changes as well as temperature influences the structure of a magnetic fluid. This work presents experimental results on changes in the ultrasonic wave absorption coefficient of EMG-605 water-based magnetic fluid as a function of the external magnetic field intensity for different rates of magnetic field changes, at different temperatures. On the basis of these studies, radii of spherical clusters formed in the fluid under the influence of an external magnetic field have been determined.

Hydrodynamic behavior of magnetically stabilized fluidized beds of magnetic particles

A theoretical analysis of beds consisting of magnetic particles and exposed to an external uniform magnetic field is presented. The external magnetic-field intensity may be strong enough so that the magnetized bed particles create significant field which distorts the external uniform field, and exert appreciable interparticle force. This complicates the hydrodynamic bed behavior much more than that observed in an uniform magnetic field in the absence of any appreciable interparticle magnetic force. This phenomenon is examined by considering the force balance on a bed particle comprising of gravitational, buoyancy, drag and magnetic forces. This has resulted in a relationship involving the minimum bubbling velocity, the corresponding voidage value and other parameters. Available and new experimental data are discussed on the basis of this theoretical analysis. This treatment leads to an enhanced understanding of the magnetically stabilized and partially stabilized magnetofluidized beds over a wide gas velocity and magnetic-field intensity ranges.

High-Frequency and -Field Electron Paramagnetic Resonance of High-Spin Manganese(III) in Porphyrinic Complexes.

High-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopy has been used to study two complexes of high-spin manganese(III), d(4), S = 2. The complexes studied were (tetraphenylporphyrinato)manganese(III) chloride and (phthalocyanato)manganese(III) chloride. Our previous HFEPR study (Goldberg, D. P.; Telser, J.; Krzystek, J.; Montalban, A. G.; Brunel, L.-C.; Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1997, 119, 8722-8723) included results on the porphyrin complex; however, we were unable to obtain true powder pattern HFEPR spectra, as the crystallites oriented in the intense external magnetic field. In this work we are now able to immobilize the powder, either in an n-eicosane mull or KBr pellet and obtain true powder pattern spectra. These spectra have been fully analyzed using spectral simulation software, and a complete set of spin Hamiltonian parameters has been determined for each complex. Both complexes are rigorously axial systems, with relatively low magnitude zero-field splitting: D approximately -2.3 cm(-)(1) and g values quite close to 2.00. Prior to this work, no experimental nor theoretical data exist for the metal-based electronic energy levels in Mn(III) complexes of porphyrinic ligands. This lack of information is in contrast to other transition metal complexes and is likely due to the dominance of ligand-based transitions in the absorption spectra of Mn(III) complexes of this type. We have therefore made use of theoretical values for the electronic energy levels of (phthalocyanato)copper(II), which electronically resembles these Mn(III) complexes. This analogy works surprisingly well in terms of the agreement between the calculated and experimentally determined EPR parameters. These results show a significant mixing of the triplet (S = 1) excited state with the quintet (S = 2) ground state in Mn(III) complexes with porphyrinic ligands. This is in agreement with the experimental observation of lower spin ground states in other metalloporphyrinic complexes, such as those of Fe(II) with S = 1.

Magnetohydrodynamics with regard to electron inertia: Some exact solutions

Magnetohydrodynamic (MHD) equations are derived with the finite electron mass taken into account. The low-frequency spectrum of a cold two-component plasma can be described using these equations. In the linear approximation, the MHD equations lead to results coinciding with those of multifluid hydrodynamics. An exact solution to the generalized MHD equations is obtained as a stationary nonlinear wave. A soliton-like solution is found for a wide range of Mach numbers and external magnetic field intensities.

Magnetoresistance effect in bulk samples of La 0.67Ca 0.33MnO 3 under a low magnetic field

The magnetoresistance effect of bulk samples of La 0.67Ca 0.33MnO 3, prepared by the sol–gel method has been studied under a low applied magnetic field. Quite a large (−37%) negative magnetoresistance ratio (MR) has been obtained at a relatively `higher' temperature (190 K) with an applied external magnetic field intensity as low as 0.6 T. Observation of the MR peak at a temperature greater than the insulator–metal transition temperature has been made for the first time.

磁場誘起マルテンサイト変態を利用したｂｃｔ窒化鉄の作製

Foils of the γ-FeN phase were prepared by the conventional gas nitrification method in an NH3 + H2 atmosphere. We found the γ-FeN phase field extends beyond 11.1 at%N at 660°C, which is the stoichiometric composition of Fe16N2. The γ-FeN phase with 9.8 at%N is transformed into a mixture of the α' and γ phases by cooling to below 180 K. An intense external magnetic field at 4.2 K is found to drive the martensitic transformation occurring in the γ phase, and a field of 170 kOe reduces the amount of residual γ phase from 38% to 16%. This results in a drastic increase in the spontaneous magnetization from 147 emu/g to 198 emu/g.

Heat transfer from an immersed surface in a magnetofluidized bed

Heat Transfer from an immersed horizontal cylindrical heat-transfer probe in an air-fluidized bed of iron shots exposed to an external magnetic field has been investigated. The probe is equipped to provide both total and local heat-transfer coefficients at different axial and angular positions. The fluidizing-air velocity and external magnetic-field intensities are varied to bring about different fluidization regimes starting from fixed-bed, magnetically stabilized-bed, partially stabilized-or bubbling-bed, and frozen-bed regimes. The nature of heat transfer is interpreted in all these regimes and conditions are identified where advantages of magnetic bed stabilization can be enjoyed without loss of heat-transfer rates.