De Magnetic Field Research Articles

Optimal segmentation of Halbach sphere

AbstractThe direction of magnetization in which the magnetic field becomes the strongest in the x‐axis direction in the spherical coordinate system is used. Its magnetic field depends on the φ direction in the spherical coordinate system, that is, strongest at the top (φ = 0) and the bottom (φ = π), and the side (φ = π⁄2) becomes the weakest. Therefore, when segmenting, it was divided to include the top and the bottom parts. In addition, in order to make it an optimal segmentation, it is effective to make the range of the top and bottom divisions wide, the sides narrow, and the direction of magnetization close to the top and the bottom directions. By optimizing in this way, the magnetic field is larger than the equal division. For example, it was about 1.09 times stronger in three divisions. This was confirmed by the experiment. However, there is a problem that the demagnetic field in the center becomes strong by optimizing. The type of division which is strong in this problem is also introduced.

Study of Heat Treatment Effect in MnCoGe Compound on Stucture and Electric Properties

A comprehension about magnetic refrigeration which develops strong materials as the refrigerant will be explained and develop in this project. Magnetic refrigeration comes from magnetocaloric effect (MCE) which is magnetic material known as refrigerant that react with a magnetic and demagnetic field. Refrigerant plays the roll in control the performance of magnetic refrigerator. One of interesting refrigerant is MnCoGe compound which found very favourable in produce high value of MCE. From this point of view, the process of producing of MnCoGe using ball milling treatment and heat treatment had been studied. Variable of temperature in heat treatment process and following by cooling down to room temperature have been implemented in order to produce good structure of MnCoGe compound. Furthermore, from structure properties measurement found this compound produce three type of structures which are hexagonal, orthorhombic and mix structure (hexagonal and orthorhombic). Based on the different temperature of heat treatment, it indicate for 1500o C and 1200o C treatment are dominant to the hexagonal structure type, then for 1000o C dominant to the orthorhombic structure and lastly for 1100o C dominant to mix structure. Electric properties measurement found the frequency play the role in change the structure as well as in 1000o C compound was found below 5M Hz frequency show the hexagonal structure and when increasing above 5M Hz the pattern change to orthorhombic structure respectively. Moreover, for the permittivity measurement it gives the information about conductivity and tan delta value. Systematically at 1000o C compound found this material is more to conductor behavior compare others compound. Therefore, when the temperature is increased to 1100o C, 1200o C and 1500o C then the conductivity value decreasing and its resistivity value become increasing.

Fabrication of an optimized hexapole magnet for a 14.5 GHz electron cyclotron resonance ion source

A hexapole magnet for a 14.5 GHz electron cyclotron resonance (ECR) ion source, where the maximum radial field on the wall of the plasma chamber is higher than 1.1 T, has been designed and fabricated. The size of the outer diameter and the number of the sector of the hexapole are optimized for a 14.5 GHz ECR ion source with the help of a three-dimensional field calculation code. Moreover, to make a strong and long-life magnet against the demagnetic field on the hexapole multilayered structure in radial and axial directions is considered in the design. The distributions of the demagnetic fields are estimated by the calculation of the radial field in a hexapole magnet and the axial field from the solenoid coils. Proper grades of magnetic materials depending on the strength of the demagnetic field are applied for the different layers. The magnetic fields of the measured and calculated ones have been compared.

Variation in magnesium isotopic composition during zone recrystallization of MgCl2·6H2O

The variation in Mg isotopic composition during MgCl2·6H2O zone recrystallization was studied. It was shown that light isotope 24 Mg enrichment occurs at the crystal end to which the recrystallization zone moves. Isotopes 25 Mg and 26 Mg concentrate in the initial crystallization zone. When the molten zone is exposed to a de magnetic field or direct current, the separation factor increases. The data obtained were compared with data on magnesium isotope separation by other physicochemical methods.

High-drive-field domain wall dynamics in low-damping garnet films

Domain wall (DW) dynamics in a low-damping YBiFeGa film with perpendicular magnetic anisotropy was studied under FMR conditions. Measurements were carried out under radial expansion of magnetic bubbles in high pulsed drive fields and in an in-plane de magnetic field. A high-speed image recording technique was employed. The pattern of the dependence of DW velocity on drive field for the parts of the DW oriented parallel and perpendicular to the in-plane field was established. In all cases, this dependence contains a saturation region in which the DW velocity increases noticeably with increasing in-plane field. The experimental data obtained do not agree with theory. A possible explanation for this discrepancy is proposed. The onset of spatially periodic distortions in a moving DW is discussed.

Field and frequency dependences of ac magnetic measurements as a probe of nonlinear flux diffusion in high-temperature superconductors

Abstract We studied the frequency and field dependences of harmonie magnetic susceptibilities by numerically solving the diffusion eauation for the magnetic flux, incorporating both creep and flow processes in a collective pinning approach. In particular the irreversibility (H, T) line is analysed and discussed in terms of the de magnetic field dependence of the onset temperatures of the first and the third harmonics respectively. It is shown that, in our conditions, the Taff resistivity is the dominant process for the flux diffusion at the onset temperature of the imaginary part of the first harmonie. On the contrary, the onset of the third harmonie is determined by the cross-over between processes dominated by the Taff and the creep resistivities.

A spin wave resonance study on reentrant Au 77Fe 23 films

Thin films prepared by both flash and slow evaporation of the bulk Au 77Fe 23 alloy have been studied by electron spin resonance (ESR) technique at the temperature range between 77–300 K. A series of spin wave resonance (SWR) peaks were observed at all temperatures when the external de magnetic field is applied along the directions lying in a small angular interval with respect to the film normal. The classical spin wave model has been used to analyze the experimental data. The magnetic parameters, such as exchange stiffness constant, the effective bulk and the surface anisotropy energy parameters of the system have been derived as a function of temperature. While the easy plane surface anisotropy almost remains constant, considerable increments were found in the exchange parameter, the magnetization and the linewidth with decreasing temperature. The SWR linewidths for the films obtained by slow evaporation at higher substrate temperatures are noticeably smaller compared to those of the film prepared by flash evaporation technique.

Reactor modeling of magnetically enhanced capacitive RF discharge

Magnetic and collisional effects on capacitive radio frequency (RF) discharges for magnetically enhanced reactive ion etching (MERIE) are investigated. Using simplified plasma and sheath models, a collisional magnetic-sheath equation that governs the sheath dynamics under a de magnetic field crossed with a sinusoidal RF electric field is obtained. The sheath equation includes global effects of the bulk plasma. Together with the power-balance equation and the particle-conservation equation, the sheath equation is used to extract a circuit model and predict the electrical behavior of MERIE reactors. Numerical results on the plasma density and the power in MERIE reactors agree well with reported experimental results and the circuit model describes the repeated discharge properties well.

Magnetic flux quanta in annular Josephson junctions in a barrier-parallel de magnetic field

Flux quanta (fluxons) trapped in an annular Josephson junction reside in a spatially periodic pinning potential when a uniform external magnetic field is applied parallel to the plane of the junction's tunnel barrier. We investigate the fluxon behavior by measuring the current versus voltage curves, the magnetic dependence of the junction critical current, and by means of spatially resolved measurements imaging the pinned fluxons. We derive the fluxon potential energy including fluxon-fluxon interaction. Fair agreement of this calculation with our experimental results is obtained.

Analysis of a tunable frequency-selective surface on an in-plane biased ferrite substrate

The response characteristic of a frequency-selective surface (FSS) made up of a Jerusalem cross on a in-plane biased ferrite substrate is analyzed with the full-wave moment method. It is shown that the resonant frequency of a FSS can be dynamically adjusted by changing the de bias magnetic field. For normal incidence of the plane electromagnetic wave, a resonant-frequency shift of about 5 GHz can be obtained by tuning the bias de magnetic field. It is further proved that it is easier to get the shift of resonant frequency of a FSS for the case of the Jerusalem cross than for the cross dipole for a given range of bias magnetic field. For an oblique incidence of 45°, about a 3-GHz resonant-frequency shift can be easily achieved. © 1996 John Wiley & Sons, Inc.

Fabrication and characterization of highly textured (Bi,Pb)2Sr2Ca2Cu3Ox superconducting ceramics using high magnetic field and cold isostatic pressing

High textured (Bi,Pb)2Sr2Ca2Cu3Ox ceramics have been fabricated by aligning deflocculated flakes of (Bi,Pb)2Sr2Ca2Cu3Ox suspended in an organic medium by means of a high de magnetic field (6 T) at room temperature followed by cold isostatic pressing. The proportion of the (Bi,Pb)2Sr2Ca2Cu3Ox phase in the precursor powder was carefully controlled, and the characteristics of the powder, such as size distribution and morphology, were determined. A high degree of grain alignment was found in the specimens after the magnetic alignment, although the bulk density of the materials was low. Cold isostatic pressing substantially increased the density of the magnetically prealigned specimens which also resulted in a slight decrease in the degree of grain alignment. This minor realignment was found to be due to the various kinds of processing defects that appeared in the specimens during compaction due to the grinding and cracking of the grains and their interlocking. The microstructural and superconducting properties of the sintered ceramic have been studied using texture goniometry, high resolution scanning electron microscopy, transmission electron microscopy, ac magnetic susceptometry, and critical current measurements.

Demonstration of a repetitively pulsed magnetically gain-switched chemical oxygen iodine laser

Experimental results are presented for the power output of a gain-switched chemical oxygen iodine laser using a magnetic switch based on the Zeeman effect. Switching is achieved using rapid field nulling of a permanent de magnetic field. A peak-to-average power enhancement factor of 12.7 has been demonstrated at a rep rate of 500 Hz. Numerical and analytic models are developed to calculate the output spike and are compared with experimental results.

Surface resistance measurement of superconducting YBa2Cu3O7 in a magnetic field

We report on the magnetic-field dependent surface resistance of polycrystalline YBa2Cu3O7 (Tc ≃ 92 K), measured using a brass cylindrical cavity resonator, operating at 16.5 GHz in the TE011 mode. A de magnetic field Happ is applied parallel to the superconducting sample surface, and the temperature dependence of the surface resistance is measured for four different values of Happ (0 T, 0.22 T, 1 T, 5 T). An effective medium theory and the two-fluid model are used to fit the surface resistance versus temperature measurements both in zero field and for various applied fields. These results are applied to characterize the microwave properties of a polycrystalline ceramic superconductor.

A resonant-type amorphous ribbon magnetometer driven by an operational amplifier

The resonant-type magnetometer presented here is composed of a high gain operational amplifier and a resonant circuit with an amorphous core connected to the input terminals of the operational amplifier. In this circuit, the operational amplifier with high input impedance operates a voltage switching element to invert the polarity of the driving voltage. Therefore, under the current source excitation, the duty ratio of the driving voltage is sensitive to a very weak dc magnetic field applied to the core. It is shown that the absolute value and the polarity of the mean value of the driving voltage can be converted into corresponding strength and direction of the de magnetic field. The maximum sensitivity of the magnetometer was around 12.4 V/Oe and the resolution was around 1.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> Oe.

Collective modes of semiconducting space charge layers

A self-consistent energy functional perturbation theory is used to evaluate the linear response of the quasi-two-dimensional electron gas of a surface space charge layer or quantum well to an external perturbation with arbitrary space and time dependence. Collective modes of the system are determined from the poles of the appropriate response function. In the absence of a de magnetic field intersubhand collective modes as well as the usual two-dimensional plasmon with ω p(q) −(2πN inve 2q/mϵ s) 1 2 are found. In the presence of a de magnetic field both spin waves spin independent excitations occur. One example of the latter is the hybrid magneloplasma waave with ω 2 − ω 2 e + ω 2 p ( q).

Endor induced electron paramagnetic resonance: Application to the resolution of overlapping spectra

A technique for resolving overlapping EPR spectra is demonstrated in a study of X- and γ-irradiated crystals of 1,1-cyclobutanedicarboxylic acid. Discrimination of overlapping spectra is accomplished by recording the electron paramagnetic resonance desaturation induced by a radiofrequency field which excites nuclear spin transitions of only one of the several paramagnetic species present. This spectrum, referred to as ENDOR induced electron paramagnetic resonance (EI-EPR), is the difference between the ordinary partially saturated EPR spectrum and the EPR spectrum recorded in the presence of a resonant radiofrequency field. An instrumental arrangement for the fast and convenient measurement of EI-EPR at several Zeeman modulation frequencies is described. The technology is employed to resolve the complicated EPR spectrum which arises from three distinct radical species existing in radiation damaged 1,1-cyclobutanedicarboxylic acid. The EI-EPR, electron nuclear double resonance, and electron electron double resonance spectra of the alicyclic and aliphatic radical are recorded as a function of temperature and crystal orientation. EI-EPR is demonstrated to permit resolution of EPR spectra due to different radical species, different molecular conformations of a given species, and radicals in different (magnetically inequivalent) sites in the crystal unit cell. All alicyclic radicals exhibit temperature dependent beta hyperfine interactions although alpha and gamma interactions show little variation with temperature. EI-EPR signal intensities are found to vary with nuclear transition probability, relaxation parameters which characterize the various transitions, and with the applied de magnetic field (i.e., the nuclear Zeeman interaction).

Measurement of Microwave Faraday Effect in n‐Type Silicon

AbstractMeasurements of the Faraday rotation in n‐type silicon have been performed at room and at low (93 °K) temperatures. A crossed‐waveguide technique (18.0 to 26.5 GHz), similar in principle (but in a simplified form) to the technique of Bouwknegt and Volger [4], has been used for the measurements. The rotation has been studied as a function of de magnetic field up to 10 kOe. The effect of multiple reflections has also been studied at low temperatures. The theory of the Faraday effect in anisotropic n‐silicon, previously developed by the authors [3], is modified taking into account the contribution of mixed scattering of lattice and impurities. The modified theory is compared with the experiment, and an estimation is made of the relative importance of the impurity over the lattice scattering. It is shown that impurity scattering gives an appreciable contribution to the rotation.

Pseudopotential approach to magnetic energy bandstructure and magnetic breakdown in metals

The orthogonalized plane wave method of energy bandstructure calculation is generalized to the case of a metal under the influence of an external de magnetic field, with the magnetic translational symmetry taken into account fully. The magnetic field-dependent effective lattice potential or pseudopotential derived from it is interpreted as a “magnetic” pseudopotential and shown to depend only weakly on the magnetic field strength so that, to a good approximation, it can be replaced by an ordinary pseudopotential, and treated as a perturbation in the calculation of magnetic energy bands and galvanomagnetic properties in nearly-free-electron metals. Physical properties connected with the phenomenon of magnetic breakdown, in particular the Landau level broadening, which were previously shown by Pippard, Zak and others to be proportional to an unspecified pseudopotential, are reformulated in terms of the magnetic pseudopotential. The convergence of the method is also discussed.

The interaction of optical phonons with magnetoplasma waves in ionic semiconductors

The interaction of magnetoplasma waves with optical phonons is investigated for propagation both parallel and perpendicular to the external de magnetic field. The low frequency region is considered where helicons and Alfven waves propagate for uncompensated and compensated materials, respectively. The results are applied to degenerate, ionic semiconductors where the plasma frequency is much larger than the infrared dispersion frequency and the cyclotron frequency. The theory is applied to heavily-doped InSb for the case of helicon-optical phonon interactions.