Measurements and self-consistent calculations of the magnetic fields near a perpendicular medium

Several models used to describe magnetic fields from perpendicular media and heads have been evaluated with the high-resolution field measurement system. Perpendicular fringing fields near statically written magnetization patterns were computed using an iterative self-consistent technique utilizing a hyperbolic-tangent and a Stoner-Wohlfarth hysteresis model. The fields predicted by both theories were compared with those measured from magnetization patterns statically written in two different Co-Cr media with a ring head and a single-pole head where the media had either been presaturated or demagnetized. The field distributions predicted by both theories were in generally good agreement with the measurements; the theoretical amplitudes were within 20 percent for the hyperbolic-tangent model, but significantly larger amplitude errors were found for the Stoner-Wohlfarth model. Write fields were measured from a ring head and a single-pole head, and a theory for each of the heads was shown to be in excellent agreement with the measurements.     

Measurements of surface magnetic fields of perpendicular and longitudinal magnetic recorded transitions using a magnetoresistive transducer

Quasi-static recording experiments employing a hybrid single-pole-type write head and a vertical magnetoresistive transducer (MRT) read head are presented. The MRT is shown to be able to measure asymmetries of the remanent magnetization of transitions recorded in perpendicular and longitudinal media. The effects of varying the write field angle by adjusting the write shim placement with respect to the auxiliary pole is shown to be useful in determining the resultant remanent magnetization. Dynamic recording responses correlate with the quasi-static measurements. A model of recorded transitions is presented which combines in-plane arctangent and vertical complementary arctangent remanent magnetization distributions.     

Smoothing and differentiating experimentally measured magnetic field distribution in the gap of cyclotron electromagnet

We describe an algorithm for smoothing and differentiating an experimentally measured magnetic field distribution defined in a cylindrical coordinate system and set in the form of a table. Formulas for the local smoothing and differentiation of magnetic induction over arrays of various dimensions (3 × 3 × 3, 5 × 5 × 5, etc.) are presented. The obtained magnetic field components obey the Maxwell equations. Principles of the optimum choice of the smoothing step are considered and estimations of the accuracy and reliability of the computational process are given.     

Measurements of the magnetic properties of magnetic liquids in waveguides

Measurement Techniques - Waveguide methods for determining the magnetic properties of magnetic liquids are proposed. The methods are based on the use of the results of measurements of the position...     

Lateral magnetic inhomogeneities in Co-Cr layers detected by FMR

Co-Cr layers deposited on Ge underlayers were investigated with ferromagnetic resonance (FMR). The thickness of the Co-Cr layers and the substrate temperature (T_s) during deposition were varied. Measurements with a vibrating sample magnetometer showed that an increase of T_s results in an increase of both the bulk saturation magnetization M_s and the perpendicular coercivity H_c^⊥. The FMR spectra, obtained with the applied field perpendicular to the sample, showed two resonances for all layers. The effective anisotropy field is positive for both resonances. The difference in effective anisotropy field does not change with thickness of the layer, but increases with increasing T_s. From this it is clear that the two resonances are not due to magnetic inhomogeneities in the growth direction, but must be due to lateral magnetic inhomogeneities. Inhomogeneities in composition, resulting in different values of M _s, or in geometric structure, resulting in different values of the demagnetizing factor N_d, are the most probable causes of the observed effects     

Measurements of photon spectra in mixed fields at a nuclear installation

This paper describes the measurements of photon spectra in mixed neutron/photon radiation fields at a few locations in a nuclear reactor. The measurements were performed inside the containment of reactor 4 at the Swedish reactor site Ringhals, with a Ge-detector (4%). The measurements were carried out as a part of a EURADOS project in co-operation with the Swedish authorities and the reactor operating company. The measurements showed that a large fraction of the photons are high-energy photons (up to 7.6 MeV). This implies that GM-based photon detectors will overread in these fields since this type of detector generally overestimates the ambient dose equivalent in 6–7 MeV photon fields. The measurements also indicated that the photon field was almost isotropic, which in turn implies that the effective dose as well as the personal dose equivalent will be lower than the ambient dose equivalent.     

On the interaction of magnetic fields and magnetic shields

Some general mathematical expressions have been derived for the induced self and mutual inductances of the wires inside a cylindrical ferromagnetic shell. An application of these results is given. It is shown that the effect of the ferromagnetic shell on the inductances of the multiconducting wires is strongly geometry dependent; the closer the wires to the magnetic shell, the stronger the effect. For wires in the center of the cylinder, no significant result will be caused by the presence of the magnetic shell.     

Fractal dimension of structural inhomogeneities in granular YBCO superconductor in magnetic field

The influence of a fractal character of the structure of an YBCO type high-temperature superconductor on its current-voltage characteristic in a magnetic field has been studied. The fractal dimension and connectivity index of vortex transport channels are determined as functions of the magnetic field strength. It is established that the glassy state index corresponds to that of a vortex glass.     

Synthesis of magnetic fields

The paper deals with some problems of magnetic fields synthesis, depending on determination of the current density distribution, which generates the required magnetic field in the investigated region. Such problems can be reduced to the linear, or nonlinear Fredholm integral equations of the first kind, or to the set of these equations. Fredholm integral equation of the first kind belongs to the class of the ill-posed problems, and for its solving the method of regularisation has been used. In the paper there are given some useful results of synthesis of magnetic fields in few practical configurations.     

Self-organization in a layer of magnetic fluid in strong electric fields

The effect of a polarizing voltage on the electrical properties of a magnetic fluid confined between the plates of a plane capacitor connected to a series resonance circuit has been studied. The magnetic fluid layer features the formation, development, and self-organization of aggregates with dimensions on the order of several millimeters. These processes influence the physical properties of the magnetic fluid layer.     

Measurements of radiation fields around high-energy proton accelerators

Monitoring of ionising radiation around high-energy particle accelerators is a difficult task due to the complexity of the radiation field, which is made up of neutrons, charged hadrons, muons, photons and electrons, with energy spectra extending over a wide energy range. The dose-equivalent outside a thick shield is mainly owing to neutrons, with some contribution from photons and, to a minor extent, the other particles. Neutron dosimetry and spectrometry are thus of primary importance to correctly evaluate the exposure of personnel. This paper reviews the relevant techniques and instrumentation employed for monitoring radiation fields around high-energy proton accelerators, with particular emphasis on the recent development to increase the response of neutron measuring devices > 20 MeV. Rem-counters, pressurised ionisation chambers, superheated emulsions, tissue-equivalent proportional counters and Bonner sphere spectrometers are discussed.     

Critical magnetic fields of a Kondo superconductor:ZnMn

The superconducting critical fields of pure Zn and of a series ofZnMn alloys have been measured as a function of temperatureT down to 0.06 K. The critical fields have been used to calculate the entropy difference between the normal and superconducting states. For all the alloys studied, the entropy in the superconducting state is proportional toT asT 0, indicating a finite density of states at the Fermi energy. We interpret this result as evidence for the existence of localized bound states within the energy gap centered at the Mn impurities. Results obtained for the depression ofT _c , for the critical field atT=0, for the jump in specific heat atT _c , and for the law of corresponding states are also presented and compared with the predictions of the Abrikosov-Gor'kov theory. A simple expression relating the critical fields of these alloys to the Mn concentration has been found to be in very good agreement with experiment.Research supported by the National Science Foundation.     

Electron transitions in strong magnetic fields

Various types of electron transitions in strong magnetic fields due to qualitative changes of the energy spectrum of electrons (and hence of properties of materials) were predicted and observed at certain critical values of the magnetic field. Metallic and semiconducting Bi-Sb alloys were investigated in the concentration range of Sb up to 8 at % and from 8 at % to 16 at % correspondingly. The transversal and longitudinal magnetoresistance measurements on Bi-Sb alloy single crystals were performed at various orientations of current and fields relative to the crystalline axes. The measurements were performed in magnetic fields up to 600 kOe.at temperatures from 4.2 to 77°K. The following types of electron transitions were discovered: (a) semiconductor-metal transition; (b) a transition from a semiconducting state into a state with an abnormally small energy gap between the zones referred to as a quasimetallic; (c) a transition semiconductor-quasimetal-semiconductor; (d) a transition semiconductor-quasimetal-semiconductor-metal; and (e) metal-semiconductor transition.     

Effects of magnetic fields on cracks in a soft ferromagnetic material

The 2D problem of a soft ferromagnetic solid with a finite crack under a uniform magnetic field has been studied based on the linear theory of Pao and Yeh. Especially, in this work, the Maxwell stresses induced by the applied magnetic field are taken into account in the boundary conditions not only along the crack surfaces, but also at infinity. Based on these boundary conditions, the related boundary-value problem is solved by using Muskhelishvili’s complex variable method to obtain the complex potentials. Thus, it is found that the obtained complex potentials are constant, which indicates that both magnetic fields and stress are uniform in the solid. This implies that if only a pure magnetic field is applied, it has no effects on a crack in a soft ferromagnetic solid. To confirm this result, the same boundary-value problem is solved by the integral transform technique, which shows the same finding as that by using the complex variable method. This outcome is consistent with available experimental data but different to previously published theoretical results.     

Diffusion in a porous system in crossed electric and magnetic fields

Diffusion in crossed electric and magnetic fields is considered; measurements are reported on accelerated diffusion in the extraction of low-molecular-weight fractions (hemicelluloses) from cellulose and of copper salts from viscose fiber.Notation j₁ current density in liquid - j_p current density inside particles - c concentration in liquid - c₀ concentration in particles - t time - D₁=mD mass-conduction factor [17] - D diffusion coefficient - m porosity - D_c=D(m/m_v) concentration-conduction factor [17] - m_v volumetric porosity - x coordinate - s=2.46 design factor (for a film) - film half-thickness Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 5, pp. 831–838, November, 1976.     

Modeling of fields in magnetic drum separators

Little analytical work has been done in evaluating the periodic magnetic fields and associated field gradients which determine small particle behavior in drum separator systems. One of the few investigations of recent times is that of W. F. Brown, Jr. [1] in which experimental data on field values are fitted to a Fourier series expressed in terms of the azimuthal angle about the drum axis. Here, a simpler Fourier series for linear periodic field arrays is adapted to the cylindrical geometry of drum separators, enabling for the first time, the construction of satisfactory equations of motion for small magnetic particles in such systems.