Magnetic Charge Distribution Research Articles

Electrodynamics of Bose-Einstein condensates in angular motion

A theory determining the electric and magnetic properties of vortex states in Bose-Einstein condensates (BECs) is presented. The principal ingredient is the Lagrangian of the system which we derive correct to the first order in the atomic centre of mass velocity. For the first time using centre of mass coordinates, a gauge transformation is performed and relevant relativistic corrections are included. The Lagrangian is symmetric in the electric and magnetic aspects of the problem and includes two key interaction terms, namely the Aharanov-Casher and the Roentgen interaction terms. The constitutive relations, which link the electromagnetic fields to the matter fields via their electric polarisation and magnetisation, follow from the Lagrangian as well as the corresponding Hamiltonian. These relations, together with a generalised Gross-Pitaevskii equation, determine the magnetic (electric) monopole charge distributions accompanying an order n vortex state when the constituent atoms are characterised by an electric dipole (magnetic dipole). Field distributions associated with electric dipole active (magnetic dipole active) BECs in a vortex state are evaluated for an infinite- and a finite-length cylindrical BEC. The predictd monopole charge distributions, both electric and magnetic, automatically satisfy the requirement of global charge neutrality and the derivations highlight the exact symmetry between the electric and magnetic properties. Order of magnitude estimates of the effects are given for an atomic gas BEC, superfluid helium and a spin-polarised hydrogen BEC.

Compensation for spurious signals due to misalignment of magnetic axes of a differential magnetic-modulation transducer. II. Theory

Calculations of the compensating field as functions of operating parameters of a compensating element based on the model of axially symmetrical distribution of surface magnetic charges are discussed. The efficiency of the compensation for spurious signals due to the misalignment of magnetic axes of a differential magnetic-modulation transducer and the transverse component of the terrestrial magnetic field is strongly affected by the selection of the optimal length of the compensating element, its diameter, shape, separation from the magnetically sensitive element, and other factors.

Perforated tips for high-resolution in-plane magnetic force microscopy

We describe a technique to modify batch-fabricated magnetic force microscopy (MFM) tips to allow high resolution imaging of the in-plane components of stray field. A hole with a diameter as small as 20 nm was milled through the magnetic layer at the apex of each tip using a focused ion beam. The tips were magnetized in the direction parallel to the sample plane. The hole at the apex forms a small pole gap, and the MFM signal arises from interaction of the stray field leakage from this gap with magnetic charge distribution of the sample. Data tracks written in recording media have been used to characterize tip performance.

<i>Hc</i>;2∼3kOeのCoCrTaPt媒体のMFMによる磁気クラスター解析

Magnetic clusters in recorded and demagnetized states were observed by MFM with tip-sample spacings from about 100 nm to 30 nm for Co69Cr21Ta2Pt8 longitudinal recording media with coercivities of 2000 to 3000 Oe. The magnetic field distribution on the medium surface was calculated from the measured MFM images, using the integrated transformation and the tip-sample distance transformation. The magnetic cluster size on the medium surface in the demagnetized state was about 130 nm for Co69Cr21Ta2Pt8 medium with Hc of 2790 Oe. The half-amplitude pulse width of the isolated magnetization transition (PW50) decreased from about 280 nm to 130 nm when z decreased from 100 nm to 10 nm. The magnetic clusters are considered to originate in the magnetic charge distribution in the local magnetization reversal region.

Phase diagram of an extended Kondo lattice model for manganites: The Schwinger-boson mean-field approach

We investigate the phase diagram of an extended Kondo lattice model for doped manganese oxides in the presence of strong but finite Hund's coupling and on-site Coulomb interaction. By means of the Schwinger-boson mean-field approach, it is found that, besides magnetic ordering, there will be nonuniform charge distributions, such as charge ordering and phase separation, if the interaction between electrons prevails over the hybridization. Which of the charge ordering and phase separation appears is determined by a competition between effective repulsive and attractive interactions due to virtual processes of electron hopping. Calculated results show that strong electron correlations caused by the on-site Coulomb interaction as well as the finite Hund's coupling play an important role in the magnetic ordering and charge distribution at low temperatures.

On the determination of the internal magnetic structure by magnetic force microscopy

In this contribution it is proven mathematically that it is in principle impossible to determine the magnetic charge distribution inside a magnetic material by a method which measures the stray field outside the sample, such as magnetic force microscopy (MFM). A general source of stray field, E σ, is defined and it is shown that different solutions can be found for E σ that result in the same stray field. It is also shown how both a perpendicular and a longitudinal medium can be described with the same E σ. Using the equations for stray field, resulting from E σ, it is also proven that performing the same MFM measurement at different scanning heights does not provide any new information on the stray field for sample; from a measurement at one (constant) height, the stray field at all other heights can be calculated. Moreover, the component of the field parallel to the same plane can be obtained from a measurement of the field component perpendicular to the sample plane.

Surface magnetic charge distribution of a long, thin cylinder and its edge singularity

The surface magnetic charge distributions with edge singularities are studied for a half-infinite circular cylinder with uniform permeability. The cylinder is placed in an axially uniform magnetic field. The subject of this study is the charge densities around the edges on both side and end surfaces. The charge densities over a certain distance from the edge on the side surface are regarded as constant. It is shown that an integral equation can be found for the charge density around the edge on the side surface. The unknown quantity in the integral equation is expressed as a product of a bounded function and an edge-singular power function depending on the relative permeability. The charge density on the end surface is expressed as a function of the charge densities on the side surface. Numerical calculations are carried out for various values of the relative permeability and are illustrated to clarify the surface magnetic charge densities. The charge densities around the edge are proportional to a certain inverse power of a distance from the edge. It is clarified for the first time that the edge singularity power factor increases with the relative permeability /spl mu/ and is equal to the same on the right-angled wedge of the same /spl mu/.

A Finite-Size Magnetic Monopole in Double-Potential Formalism

Using the double-potential formalism developed by Zwanziger, it is possible to construct nonsingular four-potentials corresponding to a given distribution of magnetic charge without violating the Bianchi identity. In this letter, we study a ball-like monopole with uniform distribution of magnetic charge. The corresponding four-potentials are found explicitly. We also construct the angular momentum operator of an electron in the field of such a monopole, which can be used to investigate the problem of electron-monopole scattering and to rectify Kazama–Yang–Goldhaber singularity.

Surface magnetic charge distributions of cylindrical tubes

The surface magnetic charge distributions of axially magnetized cylindrical tubes are calculated numerically by the surface magnetic charge simulation method. The obtained results are shown on the outer side surfaces, the inner side surfaces, and the end surfaces for various cases of different aspect ratio, radius ratio, and relative permeability. Using these results, the ballistic demagnetizing factors are obtained.

Magnetizing characteristics of circular cylinders in perpendicularly applied magnetic field

Uniform magnetic field is applied perpendicular to the axis of a circular cylinder with finite and constant permeability. The surface magnetic charge distributions and the ballistic demagnetizing factors for such a magnetizing field problem are calculated numerically by the surface magnetic charge simulation method. The results are shown for various cases of different aspect ratio and relative permeability.

An ultra-high resolution single-domain magnetic force microscope tip fabricated using nanolithography

An ultra-high resolution MFM tip is proposed and demonstrated. The tip consists of a /spl sim/30 nm thick ferromagnetic film coated on a non-magnetic pillar that has a diameter of 150 nm, a length over 1.5 /spl mu/m and a sharp end of a 10 nm radius. The pillar was fabricated on the apex of a commercial scanning force microscope tip using electron beam lithography. The ferromagnetic films were coated only on one side of the pillar but not on the rest of the tip. Therefore, the tip has a trough shape and a tapered end with a tip radius of /spl sim/10 nm. The ferromagnetic trough is single-domain because of its nanoscale size and shape anisotropy. Compared to conventional Ni wire tips, the new tips have a much smaller magnetic charge distribution at the end of the tip, thus offering better imaging resolution. Furthermore, they have a lower stray field, thus making them well suited to measuring soft magnetic materials. >

Effects of a highly permeable keeper layer on transition shifts for thin film media

Utilizing a time domain correlation algorithm, we observed that the readback signal for media with a soft keeper layer can be shifted from their original written locations in the hard under layer. The shift was similar to the hard-easy transition shift. It results from a change of magnetic charge distribution in the keeper layer in the read process. The effect of the keeper layer on transition shifts in the write process was insignificant.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development of a basic model for a 3-dimensional magnetic recording simulator

A basic model was developed for 3-dimensional analyses of the magnetic recording and reproducing processes. The curling magnetization reversal model used in our conventional 2-dimensional simulator was improved to calculate the 3-dimensional direction of a megnetization vector in a recoding medium. To consider the nonlinearity of a soft magnetic material, a recording head and an unser-layer of a Co-Cr/Ni-Fe double-layered medium were modeled by arctan function M-H loops. The magnetic field distribution was calculated by the magnetic charge distribution in both head and medium. The 3-dimensional distribution of the SPT head field was investigated when the head was combined with a Co-Cr/Ni-Fe double-layered medium.

Magnetic properties of small 3-d transition metal clusters: Role of the sp-electrons and spd-hybridization

The magnetic properties of small Fe N, and Cr N clusters are calculated by using a Hubbard-like Hamiltonian for spd-electrons in the unrestricted Hartree-Fock approximation. Results are given for the average magnetic moment, local moments and charge distribution within the cluster. The role of sp-electrons and sp-d hybridization are discussed by comparison with previous d-band calculations. In most cases a reduction of the average magnetic moment is obtained for Fe N clusters by including sp-electrons, whereas the oppositee happens to Cr clusters.

Nuclear moments as a test of shell-model and collective model descriptions of the nucleus

The distribution of electric and magnetic charges and currents in the atomic nucleus can be used to probe various nuclear structure aspects. We discuss, in particular, magnetic dipole and electric quadrupole moments as well as nuclear radii starting from shell-model and collective model approaches. We give attention to the relation between the free electromagnetic coupling strenghts (ep, en, gl, gs) and the corresponding renormalized quantities and to the way in which polarization properties depend on the nuclear model space chosen. The above points are largely illustrated with recent experimental data on these various static moments (μ, Q, ). At the same time, the limits of applicability of the various model calculations in extracting preclse nuclear structure information from the above data are discussed.

Deconvolution of magnetic force images by Fourier analysis

A novel technique which allows the true magnetic charge distribution of a sample to be obtained from a raw MFM image by deconvolution is presented. The formation of magnetic force microscopy (MFM) images can be considered as a convolution of the tip response function and the divergence of the sample magnetization. The key element in this method is the tip response function, which contains the information about the magnetic and geometric properties of the tip. This tip response function is obtained by imaging the flux emanating from the end of an ultranarrow single-domain nickel strip which approximates a point magnetic charge. An MFM image of recorded bits obtained with the same tip is deconvolved utilizing Fourier transformation methods. By this approach, the deconvolved image becomes tip independent and it is possible to achieve spatial resolutions as small as the width of the Ni strip, which can be 10 nm wide.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Surface magnetic charge distributions and demagnetizing factors of circular cylinders

A circular cylinder in which a relative permeability is finite and constant is considered. The surface magnetic charge distributions and the demagnetizing factors are calculated numerically by the surface magnetic charge simulation method and are shown for various cases of different aspect ratios of length to diameter and different relative permeabilities. The results are used to obtain the ballistic demagnetizing factors and to compare them with other available data. >

The use of modified surface impedance in a minimum-order boundary element method

It has previously been shown that by using both surface electric current and magnetic charge distributions, the equivalence principle provides the basis for a direct boundary-element (BE) method which can be used to give solutions to eddy-current problems in unbounded media. Use of the impedance boundary condition reduces the method to one of minimum order, but the present results show that in the presence of corners inaccurate results are obtained using the simple one-dimensional impedance value. Modification of surface impedance is shown to considerably improve the solution in the corner region. A similar result is obtained when a finite element solution of the conducting region is coupled to the BE method. The improvement in the accuracy of field quantities computed in the region of a corner in a two-dimensional problem is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrodynamics of magnetic-charge distributions for applications to chiral lagrangian theory and electromagnetic properties of hadrons

Motivated by results derived from chiral phenomenological Lagrangian field theories encompassing low-energy strong interactions and current-algebra PCAC aspects, one formulates a definite spinor quark model with attending magnetic pointlike charge. From this approach, the anomalous contribution to baryon magnetic moments can be evaluated and suppression of electric-dipole moments with time reversal invariance understood. In this paper, the different parts of the interaction Hamiltonian are discussed and the equations for the potentials are obtained explicitly. Simpler solutions showing magnetic polarizations are derived and shown to exist. Mellin transform techniques are set up to treat more general cases.

Surface source models and formulas for the magnetic field of polygonal cross section conductors

The magnetic field of long, straight conductors of arbitrary polygonal cross section, carrying current of given volume density, is modeled in terms of a distribution of fictitious magnetization inside each conductor and a distribution of fictitious surface current, using the Amperian model for magnetized media. Subsequently, this magnetization is replaced by an equivalent distribution of fictitious magnetic surface charge. As a result, the field calculation is reduced to that of the field due to a long strip of finite width, with simple distributions of surface charge and current. An elementary formula is derived for the field produced by a conductor of arbitrary polygonal cross section carrying a uniformly distributed current. The amount of computation is subsequently reduced compared to that needed for other methods, since a Laplacian scalar potential can be used in the absence of volume current density in these models.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>