横向常磁场中铁磁圆板的主共振特性与静载效应

针对横向常磁场中铁磁圆板的主共振问题进行研究.基于电磁基本理论,得到薄板在常磁场中所受的磁体力和洛伦兹力,应用哈密顿变分原理,推导出磁场中铁磁圆板磁弹性耦合横向振动微分方程.常磁场中铁磁圆板受到的磁体力为静载荷,根据伽辽金法得到周边夹支边界条件下铁磁圆板在静载荷作用下的初挠度,进一步应用多尺度法对周期载荷作用下的非线性...     

On the Elastic Coupling Through the Flux Lines and Magnetic Interaction

It is defined the magnetic interaction energy between two superconductor pieces situated in a magnetic field by using the elastic coupling through the flux lines. On this basis, it is shown that a force between a superconducting material and a source of magnetic field is always repulsive, the force between a ferromagnetic material and a source of magnetic field is always attractive and a force between a normal metal and a source of time-varying magnetic field is always repulsive.     

Micromagnetic Study of Forced Oscillation of Magnetic Domain Wall in Ferromagnetic Nanowires with Variation of Damping Constant

We have investigated a DW motion driven by AC external field with a variation of damping parameter ?? in Landau?CLifshitz?CGilbert equation as well as a variation of an oscillating force frequency by means of a micromagnetic simulation. Straight ferromagnetic wires having a DW at the wire center is considered, where the DW is assumed to behave like a free quasiparticle. With variation of strength and frequency of the external AC field, we have observed that relative phase delays between the forced DW motion and the AC field depends on the damping constant. The overall behavior is explainable with a single-degree-of-freedom model of a damped forced oscillation without a restoring force.     

Magnetic Force Microscope Contrast Simulation for Low-Coercive Ferromagnetic and Superparamagnetic Nanoparticles in an External Magnetic Field

We report the results of simulations of magnetic force microscope (MFM) contrast for low-coercive ferromagnetic and superparamagnetic nanoparticles. We show that two types of MFM contrast in the form of gaussian and ring distributions can be observed because of probe-particle interaction. We discuss stabilization of the magnetic moment of nanoparticles by an external magnetic field. We have calculated the values of stabilizing magnetic fields and their dependence on probe parameters and scanning heights.     

A general expression of magnetic force for soft ferromagnetic plates in complex magnetic fields

The experiments of ferromagnetic plates in different magnetic environments exhibit two distinct phenomena, i.e. the magnetoelastic instability of a ferromagnetic plate in transverse magnetic fields, and the increase of natural frequency of a ferromagnetic plate with low susceptibility in an inplane magnetic field. Although these two typical phenomena can be predicted separately by two kinds of theoretical models in which the magnetic forces are formulated by totally different expressions, no theoretical model has been found to commonly describe them. This makes it difficult to predict theoretically magnetoelastic interaction of a ferromagnetic structure in complex magnetic environment. A variational principle, here, is proposed to establish the governing equations of magnetoelastic interaction for soft ferromagnetic thin plate structures under complex magnetic fields. The functional is chosen as the summation of the magnetic energy and the strain energy as well as the external work from applied magnetic fields. From manipulations of the variational principle, the governing equations of the magnetic field and mechanical deformation together with an expression of equivalent magnetic force exerted on the ferromagnetic plates are obtained. It is shown that this theoretical model can commonly characterize the experimental phenomena of the magnetoelastic interaction aforementioned.     

Effect of magnetostriction on fracture of a soft ferromagnetic medium with a crack-like flaw

The magnetic‐induction field in the vicinity of an elliptical inclusion embedded in an infinite soft ferromagnetic medium is determined based on complex potential theory. By using a constitutive relation of magnetostriction for isotropic materials, the stress field in the vicinity of an elliptical flaw is obtained. Furthermore, the stress field at the tip of a slender elliptical crack is determined for the case in which only an external magnetic field perpendicular to the major axis of the ellipse is applied at infinity. The results indicate that the stress field in the neighbourhood of the tip is governed by the magnetostriction and permeability of the soft ferromagnetic material. The induction magnetostrictive modulus is a key parameter in determining which of the two mechanisms, i.e., magnetostriction and magnetic‐force‐induced deformation, is dominant in determining the stress field in the neighbourhood of the tip of a crack‐like flaw. With regard to the influence of the magnetic field on the apparent toughness of a soft ferromagnetic body with a crack‐like flaw, soft ferromagnetic materials can be roughly divided into two categories: one possesses a large induction magnetostrictive modulus and the other has a small modulus. An approximate criterion for categorizing the materials is presented. For the benefit of engineering design, the expressions of the stress‐intensity factor for these two categories of soft ferromagnetic materials are presented. The results show that the stress‐intensity factor is affected not only by the flaw geometry, but also by the permeability of the medium inside the flaw.     

Analysis of Minor Hysteresis Loops of Cold Rolled Low Carbon Steel

Minor hysteresis loops of cold rolled low carbon steel have been analyzed in connection with the rolling reduction. We found several simple relations between parameters of minor loops and obtained minor-loop properties that are independent of magnetic field amplitude and magnetic field. The properties increase with increasing rolling reduction and are in proportion to coercive force of the major loop. The present analysis method using minor loops can be applied to quantitative nondestructive evaluation of dislocation density in ferromagnetic materials     

Calculation and Analysis of the Magnetic Force Acting on a Particle in the Magnetic Field of Separator. Analysis of the Equations Used in the Magnetic Methods of Separation

This paper presents the derivation of equation for calculating the magnetic force acting on a paramagnetic ball situated in a region of a nonuniform magnetic field. We suggest the method of its extrapolation to the case of a nonlinear medium-the case of a ferromagnetic ball found under the influence of the magnetic field which is varying in a certain properly defined range. An experimental setting intended for the measurement of the magnetic force is described as well. For the first time a rigorous proof of the isodynamic magnetic field inexistence, that is a field which generates a magnetic force having the same constant direction and the same constant magnitude at each space point, is given. Moreover, using the method of conformal mappings we derive the analytic expressions for the magnetic field strength calculation in the case of a multipole system. With their help, different important features of the magnetic field behavior in this case are elucidated. The latter is done in a wide region of the geometric parameter space of the magnetic system. The interpretations of different issues discussed in the paper are compared to those that seems to be widely accepted in the magnetic methods of separation branch     

Numerical and Experimental Investigation to Reduction of Sedimentation of Particles in MRFs with Permanent Magnets

A method to reduce the sedimentation of the ferromagnetic particles in magnetorheological fluids (MRFs) is studied with numerical simulation and experiment. It shows that, making use of the magnetic field generated by a permanent magnet put simply above an MRF, the sedimentation of the particles in the MRF can be reduced remarkably. The magnetic force on a ferromagnetic particle and that on a particle chain are computed with the finite element (FE) code ANSYS. It reveals that the magnetic force on a particle-chain is much larger than the sum of the magnetic force on each individual particle in the chain without considering the interaction between the magnetized particles. The improvement of the sedimentation stability of MRF samples with permanent magnets is also investigated experimentally with a specially designed testing device, and it is found that a proper choice of the permanent magnet and the distance between the MRF sample and the permanent magnet can efficiently improve the sedimentation stability of MRFs.     

磁流变液流变特性的数值模拟分析

建立了微观颗粒的动力学模型,提出了相应的算法,模拟了二维状态下颗粒成链及其剪切流动过程,表明剪切过程中存在旧链断裂和新链形成,得到了流动时磁流变液的剪切应力,并模拟了高剪切速率下微结构的演变过程,发现新链形成速度小于旧链断裂速度,出现了剪应力下降现象.     

Fringing in tubular permanent-magnet machines: Part I. Magnetic field distribution, flux linkage, and thrust force

This paper extends an analysis developed for tubular permanent-magnet machines to account for the effect of fringing associated with the finite length of the ferromagnetic armature core. The magnetic field distribution, established by using an analytical technique formulated in the cylindrical coordinate system, provides an accurate means of evaluating the effect of the fringing flux on the thrust force and the back-electromotive force. Finite-element calculations confirm the analytically derived results. In Part II of the paper, the analysis is used to predict the cogging force that results from end effects and to facilitate minimization of the force.     

Fringing in tubular permanent-magnet Machines: part II. Cogging force and its minimization

In Part I of the paper, analytical field solutions, which account for the fringing flux associated with the finite length of the ferromagnetic armature core in tubular permanent-magnet machines, are established. In Part II, the technique is applied to both slotless and slotted machines, and the results are verified by finite-element calculations. The analytical field solutions enable the resultant cogging force associated with the finite length of the armature to be determined as a function of the armature displacement, for both radially and Halbach magnetized stators. Thus, they not only provide an effective means for evaluating the influence of leading design parameters on the cogging force waveform, but also facilitate its minimization.     

Investigation of Surface Properties of Magnetorheological Elastomers by Atomic Force Microscopy

Magnetorheological elastomers generally consist of a natural or synthetic rubber matrix interspersed with micron-sized ferromagnetic particles. The magneto-elastic properties of such a composite are not merely a sum of the elasticity of the polymer and the stiffness and magnetic properties of the filler, but also the result of a complex synergy of several effects, relevant at different length scales and detectable by different techniques. In our present work we investigate the microstructures, the surface magnetic properties, and the elastic properties of new isotropic and anisotropic magnetorheological elastomers prepared using silicone rubber and soft magnetic carbonyl iron microspheres. Similar samples were previously investigated by means of small-angle neutron scattering, which proved to be a useful method in the investigation of their microscopic properties. We combined the data from the atomic force microscopy measurements with those from small-angle neutron scattering to better understand the complicated behaviour of the studied materials. The measurements were performed by atomic force microscopy in the following modes: standard imaging non-contact atomic force microscopy, magnetic force microscopy, and nanoindentation. A comparative study of samples with different particle concentrations and strength of magnetic field applied during the polymerization process is developed.     

Zero-Temperature Study of a Tetrameric Spin-1/2 Chain in a Transverse Magnetic Field

We consider an alternating Heisenberg spin-1/2 antiferromagnetic–ferromagnetic chain with the space-modulated dominant antiferromagnetic exchange and anisotropic ferromagnetic coupling (tetrameric spin-1/2 chain). The zero-temperature effect of a symmetry breaking transverse magnetic field on the model is studied numerically. It is found that the anisotropy effect on the ferromagnetic coupling induces two new gapped phases. We identified their orderings as a kind of the stripe antiferromagnetic phase. As a result, the magnetic phase diagram of the tetrameric chain shows five gapped quantum phases, and the system is characterized by four critical fields which mark quantum phase transitions in the ground state of the system with the changing transverse magnetic field. We have also exploited the well-known bipartite entanglement (name as concurrence) and global entanglement tools to verify the occurrence of quantum phase transitions and the corresponding critical points.     

Structural magnetic strain model for magnetostrictive transducers

This paper addresses the modeling of strains generated by magnetostrictive transducers in response to applied magnetic fields. The measured strains depend on both the rotation of moments within the material in response to the field and the elastic properties of the material. The magnetic behavior is characterized by considering the Jiles-Atherton mean field theory for ferromagnetic hysteresis in combination with a quadratic moment rotation model for magnetostriction. Elastic properties must be incorporated to account for the dynamics of the material as it vibrates. This is modeled by force balancing, which yields a wave equation with magnetostrictive inputs. The validity of the resulting transducer model is illustrated by comparison with experimental data     

Traction force on paramagnetic particles in magnetic separators

The magnetic force, which attracts paramagnetic particles towards a magnetized ferromagnetic wire, is calculated for the geometry which is most likely to be used for magnetic separation. It is demonstrated that the magnetic field problem has an analytic solution, from which the maximum force is obtained analytically as a very simple expression. The choice of optimum wire diameter becomes less critical than in the estimation of Oberteuffer, since the maximum is flatter, but the position of this maximum is not changed significantly, and is the same for all practical purposes.     

Magnetoacoustic diagnostics of thin-walled ferromagnets with plane cracks

We propose a new nondestructive method for the magnetic diagnostics of ferromagnetic thin-walled structures based on the analysis of acoustic-emission signals. The distribution of the magnetic field induced in a ferromagnetic half space by a magnetic dipole located over the surface of this half space is determined. The diagrams of dependence of the stress intensity factor on the location of a disk-shaped crack in the material are constructed.     

Magnetic and screening properties of amorphous ferromagnetic ribbons

We have studied the magnetic and screening properties of cylindrical shields made of amorphous ferromagnetic ribbons. It is established that the relative magnetic permeability of this material can exceed 106. The action of an alternating decaying magnetic field (demagnetization) converts amorphous ferromagnetic ribbons into the state of anhysteretic magnetization, which is characterized by extremely high (above 2 × 10⁷) values of the relative magnetic permeability in magnetic fields at a level of 10 nT. The results of measurements were used to estimate the coefficient of attenuation of the Earth’s magnetic field inside cylindrical shields with open ends, depending on the diameter and the number of layers of an amorphous ferromagnetic ribbon.     

Magnetic Resonance Force Microscopy of a Permalloy Microstrip Array

The ferromagnetic resonance in an array of permalloy microstrips 3000 × 500 × 30 nm in size ordered on a rectangular grid 3.5 × 6 μm in size has been investigated by magnetic resonance force microscopy. The dependences of magnetic resonance force microscopy spectra of a sample on the probe–sample distance are analyzed. The possibility of detection of a ferromagnetic resonance spectrum of a single microstrip is demonstrated.