Simple Magnetic Model Research Articles

Analytical Modeling of Open-Circuit Air-Gap Field Distributions in Multisegment and Multilayer Interior Permanent-Magnet Machines

We present a simple lumped magnetic circuit model for interior permanent-magnet (IPM) machines with multisegment and multilayer permanent magnets. We derived analytically the open-circuit air-gap field distribution, average air-gap flux density, and leakage fluxes. To verify the developed models and analytical method, we adopted finite-element analysis (FEA). We show that for prototype machines, the errors between the FEA and analytically predicted results are <1% for multisegment IPM machines and <2% for multilayer IPM machines. By utilizing the developed lumped magnetic circuit models, the IPM machines can be optimized for maximum fundamental and minimum total harmonic distortion of the air-gap flux density distribution.

Loss Analysis of Permanent-Magnet Motors With Concentrated Windings—Variation of Magnet Eddy-Current Loss Due to Stator and Rotor Shapes

In this paper, we investigate losses, including magnet eddy-current loss of permanent-magnet synchronous motors with concentrated windings. A 3-D finite-element method that considers carrier harmonics of pulsewidth modulation inverters is utilized to calculate the losses in each part of the motor separately. A simple linear magnetic circuit model is also introduced in order to understand the mechanism of eddy-current loss generation in the magnet. First, the measured and calculated results are compared to verify the validity of the analysis. Next, the variation of the losses due to the stator and rotor shapes is investigated, for instance, concentrated and distributed stator windings and interior and surface-mounted permanent magnets. It is clarified that the eddy-current loss of the permanent magnet in the concentrated winding motor is much larger than that in the distributed winding motor. The difference of the loss generation mechanism due to the rotor shape is also clarified.

Dynamic Stiffnesses of Active Magnetic Thrust Bearing Including Eddy-Current Effects

The eddy currents induced in a thrust bearing result not only in a power loss of the system but also in phase lag and a decrease in magnitude of the magnetic force. Therefore, an accurate model including eddy-current effects would be highly beneficial at the design stage. We present a linear model including eddy-current effects for a typical active magnetic thrust bearing (AMTB). We define and calculate the dynamic current stiffness and displacement stiffness using both an analytical method and transient finite element (FE) analysis. We present a simple magnetic circuit model including eddy currents from which the two stiffnesses can be derived analytically. Furthermore, by using a transient analysis of the FE model, flux saturation, leakage, and fringing effects can all be taken into account. We show that the two stiffnesses have the same frequency response characteristics, both in the analytical model and from the results of the linear FE analysis, when the leakage and fringing effects are ignored. Even in the more practical case when the flux saturation, leakage and fringing effects are considered, the two stiffnesses can be considered to have the same frequency response characteristics within the 3 dB bandwidth without introducing much error. The open-loop frequency response of the two stiffnesses derived from the analytical model and the FE model agrees well with the experimental results.

Domain structures of ultrathin magnetic nanobelts

We use a simple magnetization model to determine domain structures of ultrathin magnetic nanobelts. A train of alternate domains are formed along the length direction. Optimal domain length decreases with belt width. Experimental domain length distributions of Fe bilayer nanobelts can be naturally explained. This approach should be applicable to similar nanomagnets.

A tectonic interpretation of the Marmara Sea, NW Turkey from geophysical data

Abstract Recent scientific investigations have revealed the deep structure and fault mechanisms in the Marmara Sea and surroundings. However, magnetic and gravity anomalies display interesting features which were not resolved in detail. In this paper, simple two-dimensional magnetic and gravity models are constructed utilizing parameters such as the density contrast and susceptibilities obtained from a borehole, seismic sections and field susceptibility measurements, respectively. The gravity model shows the existence of horst-like structures, as suggested previously. The top of the magnetic bodies in the Marmara Sea is close to the sea bottom. In general, these magnetic bodies are fault-related. The gravity model complies with the seismic base map, which was constructed previously. The magnetic anomalies of anomalous regions of the Cinarcik andWestern Basins demonstrate slight anticlockwise block rotations, while large anticlockwise block rotation is observed in the eastern extremity of the Marmara Sea. Geophysical data and modeling results suggest that the origin and evaluation of the Marmara Sea began with the possibility of emplacement of horst-like structures in the Central Ridge during the Palaeozoic or earlier followed by block rotations and intrusion of the magnetic material into the upper crust with sediment deposition and faulting. It can also be suggested that the horst-like structures in the central Marmara act to diffuse the propagation of the Northern Boundary Fault (NBF). This aspect is correlated with the focal mechanisms of the major earthquakes.

Effect of Axially Symmetric Magnetic Fields for Dynamics of Low-Current DC Vacuum Arc Plasma

In this paper, effects of four types of axially symmetric magnetic fields on the dynamics of low-current dc vacuum arc plasma, which is less than 30 A, were examined. Arcs were ignited by the opening of the butt contacts made of zinc. In the axial magnetic field, the arc plasma was restricted within a column, and the arc voltage rose with increasing gap length. When a magnet was arranged behind the cathode, the cathode spot rotated in the opposite direction to the Lorentz force (-J times B) on the edge of the circular-rod cathode. On the other hand, when a magnet was arranged behind the anode, the arc plasma was constricted on the anode side, and the lifetimes of the arcs became longer, although the arc voltage rose with increasing gap length. The compression effect of the axial component of the magnetic field was analyzed by introducing a simple magnetic piston model, and the experimental diameters of the arc column showed a good agreement with the model.

Remanence of Ni nanowire arrays: Influence of size and labyrinth magnetic structure

The influence of the macroscopic size of the Ni nanowire array system on their remanence state has been investigated. A simple magnetic phenomenological model has been developed to obtain the remanence as a function of the magnetostatic interactions in the array. We observe that, due to the long range of the dipolar interactions between the wires, the size of the sample strongly influence the remanence of the array. On the other hand, the magnetic state of nanowires has been studied by variable field magnetic force microscopy for different remanent states. The distribution of nanowires with the magnetization in up or down directions and the subsequent remanent magnetization has been deduced from the magnetic images. The existence of two short-range magnetic orderings with similar energies can explain the typical labyrinth pattern observed in magnetic force microscopy images of the nanowire arrays.

Anti-phase boundaries and magnetic domain structures in Ni 2MnGa-type Heusler alloys

The microstructure and magnetic domain structure of austenitic Heusler Ni 2MnGa are investigated as a function of heat treatment to study the interplay of anti-phase boundaries and magnetic domain walls. Conventional electron microscopy observations on arc-melted polycrystalline samples show that anti-phase boundaries in this system are invisible for standard two-beam imaging conditions, due to the large extinction distance of the Heusler superlattice reflections. Lorentz Fresnel and Foucault observations on quenched samples reveal a wavy magnetic domain morphology, reminiscent of curved anti-phase boundaries. A close inspection of the domain images indicates that the anti-phase boundaries have a magnetization state different from that of the matrix. Fresnel image simulations for a simple magnetization model are in good agreement with the observations. Magnetic coercivity measurements show a decrease in coercivity with annealing, which correlates with the microscopy observations of reduced anti-phase boundary density for annealed samples.

Topological Hall effect studied in simple models

Recently, a chirality-driven contribution to the anomalous Hall effect has been found that is induced by the Berry phase and does not directly involve spin-orbit coupling. In this paper, we will investigate this effect numerically in a two-dimensional electron gas with a simple magnetic texture model. Both the adiabatic and non-adiabatic regimes are studied, including the effect of disorder. By studying the transition between both regimes the discussion about the correct adiabaticity criterium in the diffusive limit is clarified.

On the Magnetic Correspondence between the Photosphere and the Heliosphere

The solar magnetic field maps every point in the corona to a corresponding place on the solar surface. Identifying the magnetic connection map is difficult at low latitudes near the heliospheric current sheet, but remarkably simple in coronal hole interiors. We present a simple analytic magnetic model (‘pseudocurrent extrapolation’) that reproduces the global structure of the corona, with significant physical advantages over other nearly analytic models such as source-surface potential field extrapolation. We use the model to demonstrate that local horizontal structure is preserved across altitude in the central portions of solar coronal holes, up to at least 30 Rs, in agreement with observations. We argue that the preserved horizontal structure may be used to track the magnetic footpoint associated with the location of a hypothetical spacecraft traveling through the solar corona, to relate in situ measurements of the young solar wind at ∼10–30 Rs to particular source regions at the solar surface. Further, we discuss the relationship between readily observable geometrical distortions and physical parameters of interest such as the field-aligned current density.

Characteristic temperature in magnetically doped amorphous semiconductors

The introduction of magnetic moments such as Gd into amorphous Si produces dramatic effects in electrical transport below a characteristic temperature ${T}^{*}$. Below ${T}^{*}$, the conductivity of the magnetically doped systems is strongly suppressed compared to equivalent nonmagnetic Y doped samples, and displays enormous negative magnetoresistance. ${T}^{*}$ occurs at relatively high temperatures $(\ensuremath{\sim}10\char21{}100\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and decreases sharply with increasing Gd concentration, passing smoothly through the metal-insulator transition. In ternary samples with both Gd and nonmagnetic Y, ${T}^{*}$ decreases strongly with increasing metallization, whether due to the addition of Gd alone or a mixture of Gd and Y. These results cannot be explained by simple magnetic interaction models, suggest the crucial role of electron screening and are reminiscent of mass enhancement behavior.

Permeability Dispersion in Ni-Zn-Cu Ferrite and its Composite Materials

The Ni0.27Zn0.63Cu0.10Fe2O4 sintered ferrite produced by a ceramic method was used for preparation of composite materials based on this ferrite and a non-magnetic polymer (PVC) matrix. The frequency dependences of complex initial permeability have been obtained in the frequency range 10 kHz to 1 GHz using impedance measurements and the contribution of two magnetizing mechanisms, domain wall motion and rotation of magnetic moment, to the permeability is discussed. In the case of composite materials, a simple magnetic circuit model approach including ferrite particle size and volume concentration effects is taken into account.

Volcanomagnetic changes accompanying the onset of the 2002–2003 eruption of Mt. Etna (Italy)

Remarkable changes in the local magnetic field were associated with the onset of the 2002–2003 flank eruption at Mt. Etna. After differential magnetic field measurements were filtered from the external noise by using adaptive filters, we recognized two stages in the total intensity changes, which are closely related to different volcanic events: (a) rapid variations of about 4–5 nT associated with October 26 seismic swarm recorded beneath the summit craters; (b) step-like variations of 9–10 nT coincident with October 27 eruptive fissures opening up in the north flank. These observations are generally consistent with those calculated from simple magnetic models of these volcanic processes, in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth. The magnetic data not only allow the timing of the intrusive event to be described in greater detail but also, together with other volcanological and geophysical evidences, permit some constraints to be set on the characteristics of propagation of a shallow dike. Firstly, at around midnight on 26 October magma was rapidly injected to a depth of 3–4 km just below the summit craters. Secondly, after 1:00 on 27 October, continued intrusion magma occurred upward and culminated a few hundred meters below the free surface fractured along a N–E direction. Thirdly, at about 2:28, magma gave rise to an explosive fissural vent at the northern base of the NE crater near 3000 m a.s.l. Finally, at about 5:00, the first eruptive fissure became active along the eastern border of the NE rift at 2500 m a.s.l. The rate of growth of the magnetic anomalies, moreover, leads to the interpretation that the magmatic intrusion travelled northward from base of the NE crater to the NE rift at approximately 14 m/min.

Direct observation of oscillatory behavior in the surface magnetization ofFethin films grown on aNi∕Cu(100)film

The surface and interface magnetic structures of Fe thin films (4-11 ML) grown on a 6 ML Ni/Cu(100) film have been directly investigated with the depth-resolved x-ray magnetic circular dichroism technique. An oscillatory behavior in the Fe surface magnetization as a function of Fe thickness is found. The spectra were analyzed with a simple magnetic model, in which only surface two layers and interface (bottom) single layer are magnetically active. The analysis clearly shows existence of an oscillatory or rotational interlayer magnetic coupling between the surface and interface of the Fe film via the inner layers with the interface magnetization essentially unchanged. Temperature dependent experiments showed that the surface magnetization vanishes with increasing temperature, while the interface one stays unchanged.

磁気飽和を考慮したＳＲＭの簡易磁気回路モデル

磁気飽和を考慮したＳＲＭの簡易磁気回路モデル

Experiments on simple magnetic model systems

In this paper we shall review the theoretical and experimental results obtained on simple magnetic model systems. We shall consider the Heisenberg, XY and Ising type of interaction (ferro and antiferromagnetic), on magnetic lattices of dimensionality 1, 2 and 3. Particular attention will be paid to the approximation of these model systems in real crystals, viz . how they can be realized or be expected to exist in nature. A large number of magnetic compounds which, according to the available experimental information, meet the requirements set by one or the other of the various models are considered and their properties discussed. Many examples will be given that demonstrate to what extent experiments on simple magnetic systems support theoretical descriptions of magnetic ordering phenomena and contribute to their understanding. It will also be indicated in which direction there is a need and/or a possibility for future work.

Field dependence of second-harmonic amplitude of magnetoimpedance in FeCoSiB joule heated wires

The existence of a second-harmonic component of the giant magnetoimpedance (GMI) voltage in an amorphous FeCoSiB Joule heated wire is analysed. The evolution of the first-harmonic component of the GMI voltage with the axial DC applied magnetic field can be suitably described in terms of the evolution of the circumferential magnetic permeability. With regard to the second-harmonic component, its amplitude sensitively evolves with the axial DC magnetic field and its appearance is associated to an asymmetry in the circular magnetization process. A simple rotational magnetization model is presented where the harmonic components of the GMI voltage are estimated through Fourier analysis.

A semiquantitative analytic model for the magnetic response of a Terfenol-D impregnated composite specimen under tension

Magnetostrictive composites have found increasing use as a tagging agent for structural integrity monitoring. A simple magnetic model based on Heisenberg–Weiss theory is put forth that provides guidance as to the physical parameters that govern the magnetic response of a Terfenol-D impregnated composite specimen in tension. Further, the model provides an effective analytic parameterization of the magnetic response, resulting from unidirectional tension, and affords estimates of these parameters.

Magnetization, Paleomagnetic Poles, and Polar Wander on Mars

Using the geometry of an areocentric dipole field, we have remodeled the anomalies observed in the Terra Sirenum and Terra Cimmeria regions by the Mars Global Surveyor (MGS). For the origin of the anomalies, we used both magnetic stripe and magnetic shell hypotheses. For magnetic stripe models, we assume that sea-floor spreading formed the anomalies in the presence of a reversing axial dipole field. We found that a simple magnetic stripe model with constant magnetization and crustal thickness results in poor agreement with the observed anomalies. However, by allowing the intensity of magnetization to vary freely between and along the stripes, a reasonable fit to the observed data can be found while maintaining the observed polarity along the stripes. Applying the simple magnetic stripe model to the Terra Sirenum and Terra Cimmeria anomalies results in best-fit spreading centers located well to the north of the surviving magnetic stripes. This could possibly explain the apparent lack of symmetry that has been noted in the anomalies. For the magnetic shell hypothesis, we assume that a monopolarity dipole field magnetized the early crust of Mars. The anomalies that persist today would then be the result of partial demagnetization of the original magnetic shell by more recent processes. The magnetic anomalies in Terra Sirenum and Terra Cimmeria are consistent with this model, especially if the magnetization of the original magnetic shell was laterally inhomogeneous. If the monopolarity magnetic shell hypothesis is correct, best-fit magnetic paleopole locations for the original magnetization lie in a sub-equatorial belt centered near the prime meridian. If the ancient magnetic pole of Mars coincided with the spin pole, this result implies that either apparent or true polar wander has occurred on Mars. Apparent polar wander would be consistent with plate tectonics having occurred after the formation of the magnetic anomalies. True polar wander has previously been proposed to explain certain morphologic features found on Mars.

Phenomenological magnetic modeling of Au:Fe:Au nano-onions

A new type of materials, the nano-onions, has been shown to exhibit GMR. These nanostructured composites consist of a nonmagnetic core coated with a thin layer of a bulk ferromagnet with a passivating nonmagnetic surface layer. The nano-onion investigated had a 3 nm Au core, a 1 nm Fe layer, and a 2 nm Au coating; all values correspond to the radius. The materials were manufactured using a sequential reverse micelle technique, detailed elsewhere. The sample preparation method produces a powder sample was cold pressed into a pellet. Magnetic investigation of the sample indicated that the material was superparamagnetic with a blocking temperature of 52 K for particles approximately 8 nm in diameter. At 10 K, the coercivity was 420 Oe, indicating a large degree of order. The GMR was measured over the entire temperature range available. At 10 K, in 5 T, a 1% MR was observed. The GMR was modeled using a simple phenomenological magnetic model initially used to study GMR granular thin films. To more accurately match the physical parameters of reverse micelles, the conventional log-normal particle size distribution was replaced with a normal distribution. The model suggested that the system consisted of an ensemble of 1.3 nm particles with a standard deviation of 0.07. The model does not detect the entire 8 nm diam, rather it detects the individual walls of the shell. In this context, it has shown that a simple phenomenological model can accurately predict the magnetic and electronic behavior of nano-onions.