Surface magnetostatic oscillations in elliptical bubble domains

A theory of surface magnetostatic oscillations in magnetic bubble domains with an elliptical cross section is presented. The dependences of the eigenfrequencies of resonant modes on the applied magnetic field are analyzed for a barium hexaferrite sample with allowance made for the change in the domain size due to a variation in the bias magnetic field. The range of frequency tuning in response to a magnetic field ranging from the elliptical instability field to the collapse field is estimated. It is demonstrated that elliptical bubble domains can be used as microminiature resonators operating in the millimeter range.     

Quantum tunneling of a Bloch line in the domain wall of a cylindrical magnetic domain

Tunneling through a vertical Bloch line (BL) defect in the domain wall of a cylindrical magnetic domain is considered. It is shown that the BL tunneling probability and the corresponding crossover temperature are determined by the vibrational spectrum of the domain. The parameters characterizing this effect are estimated for a state of the domain close to the elliptical instability state.     

Stresses in silicon crystals from ion-implanted amorphous regions

The plane elasticity problem of the interaction between an edge dislocation and an elliptical inhomogeneity is solved, and the image glide-force on dislocation is computed. Contour plots of the force exterted by either an elliptic hole (crack) or a rigid elliptical inhomogeneity show that force is stronger for more elongated shapes, and that in some cases dislocation trapping effects undergo drastic changes even for slight shape variations. The general case is investigated by means of angular plots of force. They show increasing oscillatory angular depence on increasing both elongation and shear moduli difference.     

Influence of three-dimensional inhomogeneities of the magnetic parameters on the dynamics of vortex-like domain walls

The interaction of a vortex-like domain wall moving in an external magnetic field with a three-dimensional periodic chain of cubic volumes with high values of the saturation magnetization and magnetic anisotropy constant has been investigated theoretically. It has been found that the result of the interaction depends on the initial distance between the wall and the region of inhomogeneity of magnetic parameters at the moment of turning on the external magnetic field. The pinning of domain walls near the regions with high values of the saturation magnetization and magnetic anisotropy constant has been investigated, and the anisotropy of the corresponding depinning fields has been revealed. The method of investigation is the numerical micromagnetic simulation.     

A Piezoelectric Screw Dislocation Interacting with an Elliptical Piezoelectric Inhomogeneity Containing a Confocal Elliptical Rigid Core

The electro-elastic interaction between a piezoelectric screw dislocation and an elliptical piezoelectric inhomogeneity, which contains an electrically conductive confocal elliptical rigid core under remote anti-plane shear stresses and in-plane electrical load is dealt with. The analytical solutions to the elastic field and the electric field, the interfacial stress fields of inhomogeneity and matrix under longitudinal shear and the image force acting on the dislocation are derived by means of complex method. The effect of material properties and geometric configurations of the rigid core on interfacial stresses generated by a remote uniform load, rigid core and material electroelastic properties on the image force is discussed.     

Simulation of the nonlinear dynamics of magnetic inhomogeneities in real magnets

The dynamics of domain walls (DW) in an infinite ferromagnet containing a flat layer with parameters of magnetic anisotropy and exchange interaction differing from the bulk values was investigated. The dependences of the minimum velocity of DW transmission through the defect region and the translational and pulsation modes of DW fluctuations on the parameters describing the inhomogeneity of magnetic anisotropy and exchange interaction were found.     

Theoretical calculation of the dielectric tensor and field equations in columns with elliptical cross-sections including inhomogeneous magnetized cold collisionless drift and rotating plasmas

In this paper the effects of the inhomogeneity of the density of charged particles and the initial axial, rotating and radial motion on the dielectric permittivity tensor and the field equations in a long column of multi-layer magnetized plasmas with confocal elliptical cross-sections are investigated. The elements of the dielectric permittivity tensor and the generalized field equations of each region are obtained. The field equations for hybrid modes in each region of the inhomogeneous plasma with coaxial elliptical cylindrical boundaries are presented.     

Magnetic domains perpendicular to the AC demagnetizing field in ordered Ni3Mn

Stripe domains with walls perpendicular to the AC demagnetizing field (PACD) are observed in atomically ordered, ferromagnetic NiMn with slightly more than 25 at.% Mn. Based on Lorentz microscopy and magnetic measurements. PACD is explained in terms of an inhomogeneity in the magnetic phase and coherent rotation of the magnetization in the domain.     

Effect of domain walls on the propagation of microwaves

The propagation of microwaves in ferrimagnets is affected mainly by the gyrotropic terms of the magnetic permeability tensor, due in this frequency range to ferromagnetic and exchange resonances. It is shown that the change in the gyrotropic terms in the domain wall region leads to the existence of a localized mode propagating close to the domain wall. The domain wall constitutes an optical inhomogeneity for the microwave. The reflectivity and transmittivity of a domain wall are calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 22–26, June, 1985.The authors are grateful to G. S. Krinchik for discussion of the paper.     

Influence of a magnetic-microinhomogeneity field on the stability-region boundaries of an isolated cylindrical magnetic domain

The parameters of an interaction between a cylindrical magnetic domain (CMD) and a magnetic microinhomogeneity of submicron size whose main characteristic is the magnetic dipole moment are directly calculated. For the particular system configuration, an equation is obtained for an equilibrium CMD in the field of an imperfection, and the influence of the inhomogeneity on the diameter and boundaries of the CMD stability region is found. Kaliningrad State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 76–81, May, 1999.     

A high spatial resolution 1H magnetic resonance spectroscopic imaging technique for breast cancer with a short echo time

The high sensitivity but low specificity of breast MRI has prompted exploration of breast (1)H MRS for breast cancer detection. However, several obstacles still prevent the routine application of in vivo breast (1)H MRS, including poor spatial resolution, long acquisition time associated with conventional multi-voxel MRS imaging (MRSI) techniques, and the difficulty of "extra" lipid suppression in a magnetic field with relatively poor achievable homogeneity compared to the brain. Using a combination of a recently developed echo-filter (EF) suppression technique and an elliptical sampling scheme, we demonstrate the feasibility of overcoming these difficulties. It is robust (the suppression technique is insensitive to magnetic field inhomogeneity), fast (acquisition time of about 12 min) and offers high spatial resolution (up to 0.6 cm(3) per voxel at 1.5 T with a TE of only 60 ms). This approach should be even better at 3 T with higher resolution and/or shorter TE.     

永磁体外部磁场的不均匀性研究

从永磁体的分子电流观点、退磁场、工艺等出发, 以矩形永磁体为例, 从理论上分析了影响永磁体外部磁场不均匀性的各种因素.研究结果表明, 永磁体外部磁场宏观不均匀性(好场区均匀度和面积相对大小) 和空间距离及永磁体的外形设计密切相关. 退磁场对永磁体外部磁场微观不均匀性有着复杂影响. 永磁体工艺如粉末颗粒、取向度、烧结凝固、机械加工等将影响永磁体外部磁场的不均匀性, 如磁化偏角、对称性、光滑性等. 关键词： 永磁体 外部磁场 不均匀性 退磁场     

Propagation of elliptical flat-topped beam in spatial-frequency domain

Based on a tensor method, the propagation formulae of elliptical flat-topped beam through aligned and misaligned optical systems in spatial-frequency domain are derived analytically. The derived formulae provide a powerful tool for treating the propagation and transformation of elliptical flat-topped beam through complex optical systems in spatial-frequency domain. As a numerical example, the propagation properties of elliptical flat-topped Gaussian beam in free space are studied in spatial-frequency domain.     

Analytical solutions of transient pulsed eddy current problem due to elliptical electromagnetic concentrative coils

The electromagnetic concentrative coils are indispensable in the functional magnetic stimulation and have potential applications in nondestructive testing.In this paper,we propose a figure-8-shaped coil being composed of two arbitrary oblique elliptical coils,which can change the electromagnetic concentrative region and the magnitude of eddy current density by changing the elliptical shape and/or spread angle between two elliptical coils.Pulsed current is usually the excitation source in the functional magnetic stimulation,so in this paper we derive the analytical solutions of transient pulsed eddy current field in the time domain due to the elliptical concentrative coil placed in an arbitrary position over a half-infinite plane conductor by making use of the scale-transformation,the Laplace transform and the Fourier transform are used in our derivation.Calculation results of field distributions produced by the figure-8-shaped elliptical coil show some behaviours as follows:1) the eddy currents are focused on the conductor under the geometric symmetric centre of figure-8-shaped coil;2) the greater the scale factor of ellipse is,the higher the eddy current density is and the wider the concentrative area of eddy current along y axis is;3) the maximum magnitude of eddy current density increases with the increase of spread angle.When spread angle is 180,there are two additional reverse concentrative areas on both sides of x axis.     

Depth dependence of Néel wall pinning on amorphous CoxSi1−x films with diluted arrays of elliptical antidots

Diluted arrays of elliptical antidots have been fabricated by optical lithography, electron beam lithography and plasma etching on amorphous Co₇₄Si₂₆ magnetic films with a well-defined uniaxial anisotropy. The magnetic behavior of two identical antidot arrays but with different hole depth in comparison with film thickness has been studied by transverse magneto-optical Kerr effect. Significant differences appear in the coercivity depending on whether the magnetic film is completely perforated or not, indicating a much more effective domain wall pinning process when the depth of the holes is smaller than the magnetic film thickness.     

Direct observation of condon domains in silver by Hall probes

Using a set of micro Hall probes for the detection of the local induction, the inhomogeneous Condon domain structure has been directly observed at the surface of a pure silver single crystal under strong Landau quantization in magnetic fields up to 10 T. The inhomogeneous induction occurs in the theoretically predicted part of the Condon domain phase diagram. Information about size, shape, and orientation of the domains is obtained by analyzing Hall probes placed along and across the long sample axis and by tilting the sample. On a beryllium surface the induction inhomogeneity is almost absent although the expected induction splitting here is at least 10 times higher than in silver.     

Propagation of elliptical Gaussian beam through misaligned optical systems in spatial domain and spatial-frequency domain

The propagation formulae of elliptical Gaussian beam through misaligned optical systems in spatial domain and spatial-frequency domain are investigated analytically by using tensor method. The derived formulae provide a powerful tool for treating the propagation and transformation of elliptical Gaussian beam through misaligned optical systems. As an application example, the propagation properties of elliptical Gaussian beam through a misaligned thin lens are illustrated.     

Elastic fields induced by non-elastic eigenstrains in a plane elliptical inhomogeneity existing in orthotropic media under uniform tension at infinity

This paper presents an analytical solution for the elastic fields induced by non-elastic eigenstrains in a plane elliptical inhomogeneity embedded in the orthotropic matrix under tension at infinity and inclined at any angle. The conformal transformation and complex function method for the anisotropic elastic material were used to determine the strain energies in the inhomogeneity and matrix, which were expressed by four undetermined coefficients characterizing the equilibrium boundary of the inhomogeneity due to the acting eigenstrains and external load. The use of the principle of the minimum potential energy led to analytical expressions for these coefficients and thus generated a closed-form solution for the elastic strain/stress fields. The resulting stress field in the inhomogeneity was examined and verified by checking the continuity conditions for the normal and shear stresses on the interior boundary of the matrix. Supported by the Program for New Century Excellent Talents in Universities (NCET) of the Ministry of Education of China (Grant No. NCET-04-0373) and the Program for Shanghai Pujiang Talents (Grant No. 05PJ14092)     

Magnetization behavior of nanomagnets for patterned media application

Bit patterned media (BPM) which utilize each magnetic nanostructured dot as one recorded bit has attracted much interest as a promising candidate for future high-density magnetic recording. In this study, the magnetization reversal behaviors of nanostructured L1₀-FePt, Co/Pt multilayer (ML), and CoPt/Ru dots are investigated. For Co/Pt and CoPt/Ru nanodots, the bi-stable state is maintained in a very wide size range up to several hundred nm, and the magnetization reversal is dominated by the nucleation of a small reversed nucleus with the dimension of domain wall width. On the other hand, the critical size for the bi-stability of L1₀-FePt is about 60 nm, and its magnetization reversal proceeds via domain wall displacement even for such a small dot size. These reversal behaviors, depending on the magnetic materials, might be attributed to the difference in structural inhomogeneity, such as defects. In addition to the magnetic properties, the structural uniformity of the material could be crucial for the BPM application.     

Global control of spiral wave dynamics in an excitable domain of circular and elliptical shape

Experiments performed in a thin layer of the Belousov-Zhabotinsky solution subjected to a global feedback demonstrate the existence of the resonance attractor for meandering spiral waves within a domain of circular shape. In an elliptical domain, the resonance attractor can be destroyed due to a saddle-node bifurcation induced by a variation of the domain eccentricity. This conclusion explains the experimentally observed anchoring of spiral waves at certain points of an elliptical domain and is in good quantitative agreement with numerical data obtained for the Oregonator model.