Field In Ferromagnetic Materials Research Articles

A novel approach for measuring large magnetic anisotropy energy with a limited magnetic field range

Here we propose an experimental method for determining the magnetic anisotropy field in ferromagnetic materials. Our method involves examining the small-angle variation of spontaneous magnetization by the external magnetic field and interpreting the experimental result within the framework of the Stoner-Wohlfarth model applicable to ferromagnetic materials. This method allows for the extrapolation of magnetic anisotropy fields, even when they surpass conventional measurement limits. As a result, a broad range of magnetic anisotropy fields can be ascertained using a single experimental setup. Our proposed method serves as a versatile tool for analyzing large magnetic anisotropy energy which is an important parameter for future spintronic devices.

Analysis of Magnetization Curve Approximations for Nonlinear Calculation of an Eddy-Current Field

Simulation of the eddy-current fields in the ferromagnetic materials is impossible without information on the dependence of the magnetic field induction on its intensity—the magnetic curve. Experimental determination of the magnetization curves encounters technical problems and the reference data contain, as a rule, a small number of values and they are unsuitable for direct application. For this reason, the transition from original magnetization curve to its approximation is relevant. Three very popular approximation methods of the magnetization curves in the calculation practice are considered in this article: the Frelich approximation, the Melgui approximation, and the universal Pentegov approximation. The average deviation from the original magnetization curve, difference in the average density and the calculation error of the active power are accepted as the approximation effectiveness. The experimental data about magnetization of materials with different properties were used for comparative analysis of approximations. It is shown that the minimum error in calculation of eddy-current fields is provided by the universal approximation. Replacement of the magnetization curve by other approximations may lead to calculation errors of active power exceeding 15%. The obtained results may be used for the nonlinear finite element analysis of the eddy-current field in ferromagnetic materials.

An Application of Magnetization Curve Approximations for Calculation of Eddy Current Fields in Ferromagnetic Materials

The problem of modelling eddy current fields has a great practical importance in the design and analysis of the efficiency of electrical devices. Dependences of magnetic field induction in ferromagnetic materials on its strength are needed to model the fields of eddy currents - magnetization curves. The experimental determination of the magnetization curves meets technical difficulties, and it is often impossible to determine the actual form of the magnetization curves from the reference data. This paper proposes to use the approximation of the results of experiments on the removal of magnetization curves in the calculations. The purpose of the paper is to select the optimal method of approximation from the three most popular ones in the calculation practice such as Frolich approximation, Melgui approximation, and Pentegov universal approximation. The results of experiments on the removal of the magnetization curves of materials with various magnetic properties are used for comparative analysis of the approximations. The results of the study can be used in the design of induction heating devices, the efficiency of which is determined by the configuration of the electromagnetic field.

Fast numerical calculation for crack modeling in eddy current testing of ferromagnetic materials

Eddy current testing (ECT) is a nondestructive testing method for metal materials. Numerical methods are applied to predict the ECT signals, to aid in the design of ECT probes, and to reconstruct crack shapes from their ECT signals. For the testing of nonferromagnetic materials, the high accuracy of some numerical simulation techniques has been demonstrated and several fast computational methods have been presented. However, the numerical calculation of electromagnetic fields in ferromagnetic materials remains a difficult and time-consuming task. Representing cracks in ferromagnetic materials with secondary electric and magnetic sources leads to a fast method for predicting ECT signals as presented in this article. The method developed here, that can be used to treat ferromagnetics, is an extension of the precomputed database approach based on the magnetic vector potential method. With the aid of precomputed databases, ECT signals of different cracks can be computed from changes in the secondary sources in a small region, without considering the geometries of the whole conductor. This results in fewer degrees of freedom than those of typical finite element approaches, and the method provides a forward simulator that is about 80 times faster than the conventional one without loss of accuracy, even in the case of ferromagnetic materials.

Stress and frequency dependence of the direct piezoelectric effect in ferroelectric ceramics

It is shown that at weak alternating stress the relationship between the piezoelectrically induced charge and applied stress in ferroelectric ceramics has the same form as the Rayleigh law for magnetization versus magnetic field in ferromagnetic materials. Applicability of the Rayleigh law to the piezoelectric effect is demonstrated in detail for lead zirconate titanate (PZT) ceramics. Experimental results indicate that the dominant mechanism responsible for piezoelectric hysteresis and the dependence of the piezoelectric coefficient on the applied ac stress is the pinning of non-180° domain walls. The dependence of the piezoelectric coefficient on the frequency of the driving stress is examined and is shown to be due to the frequency dispersion of both reversible and irreversible components of domain-wall displacement. Analysis of the stress dependence of the piezoelectric phase angle reveals piezoelectric hysteresis contributions that are not necessarily due to Rayleigh-type displacement of domain walls. Piezoelectric properties of a modified lead titanate composition that exhibits non-Rayleigh type behavior are examined and compared with the properties of PZT ceramics.

A time–space finite element discretization technique for the calculation of the electromagnetic field in ferromagnetic materials

AbstractThe stability of time‐stepping methods for parabolic differential equations is mostly a critical issue. Furthermore, solving such equations with a classical time‐stepping approach can be very expensive because many small time‐steps have to be taken if steep gradients occur in the solution, even if these occur only in a narrow part of the space domain. In this paper we present a discretization technique in which finite element approximations are used in time and space simultaneously for a relatively large time period called a ‘time‐slab’. This technique may be repeatedly applied to obtain further parts of the solution in subsequent time‐intervals. It will be shown that, with the proposed method, the solution can be computed cheaply even if it has steep gradients and that stability is automatically guaranteed. For the solution of the non‐linear algebraic equations on each time‐slab fast iterative methods can be used.

A numerical solution for the nonlinear diffusion equation of the electromagnetic field in ferromagnetic materials

In this paper the diffusion equation of the electromagnetic field in ferromagnetic materials is studied. The main difficulty in this equation lies in the nonlinear magnetic characteristic, that results in a nonlinear diffusion equation. To select a finite difference scheme to solve this nonlinear diffusion equation, a comparative analysis of the main difference schemes is made. Given the difficulties introduced by the nonlinear magnetic relationship we suggest an ordered comparative study.

Hyperfine interaction studies of amorphous materials using NMR

Through hyperfine interactions the electronic structure of amorphous materials can be investigated by NMR. Furthermore, the local character of these interactions makes them adequate to study the local environment and the local symmetry around the probe nuclei through the measurement of hyperfine fields and electric field gradients. We review recent NMR studies of amorphous metals from the following two points of view: (1) Electronic structure: Knight shifts and spin relaxation times in paramagnetic materials and hyperfine fields in ferromagnetic materials. (2) Local amorphous structure: topological and chemical short-range order. Emphasis will be given to the comparisons between amorphous materials and corresponding crystalline materials.

Irradiation growth due to magnetodiffusion

Irradiation growth due to magnetodiffusion, i.e. anisotropic diffusion induced by the application of a magnetic field in ferromagnetic materials, has been studied. An analogy with elastodiffusion is made, and the sink strength of dislocations is derived. The irradiation growth rate due to the resulting bias differential is calculated and compared with that due to elastodiffusion and the usual SIPA. Special features of irradiation growth due to this mechanism are outlined.

A method of calculation of transient electromagnetic field in non-linear ferromagnetic medium

The paper presents a method of calculation the transient electromagnetic field in ferromagnetic material, taking into account the real characteristics of magnetization. Using the difference method, the spatial-temporal distributions of electromagnetic field have been calculated in result of solving the non-linear partial differential equation for electric field E (in space Ω(x, t)). For the difference diagram assumed for approximation of the differential equation, the conditions of stability and convergence, and the condition of obtaining the minimum error of approximation, have been determined.

Erratum: Method of calculation of the transient electromagnetic field in ferromagnetic materials for the known vector of induction B on the surface

Erratum: Method of calculation of the transient electromagnetic field in ferromagnetic materials for the known vector of induction B on the surface

Method of calculation of the transient electromagnetic field in ferromagnetic materials for the known vector of induction B on the surface

Method of calculation of the transient electromagnetic field in ferromagnetic materials for the known vector of induction B on the surface

Zero-field pulsed spin echo spectrometer for the study of ferromagnetic materials

Complete description of a pulsed nuclear-magnetic-resonance spectrometer operating in the frequency range 100–600 MHz is presented. The spectrometer is suitable for investigating hyperfine fields in ferromagnetic materials and has some novel features. High sensitivity, simplicity of operation, and ease of tuning over the entire frequency interval are some significant characteristics of the spectrometer.

Broad band NMR spectrometer for the study of hyperfine fields in ferromagnetic materials

An untuned NMR spectrometer that may be used in either a continuous wave or pulsed (spin-echo) mode is described and results shown of measurements made at frequencies up to 740 MHz. Operation up to 1 GHz or more should be possible.

Positive muon investigation of internal fields in ferromagnetic materials

The μSR (muon spin rotation) technique enables one to measure the local magnetic field Bμ at the site of an interstitial positive muon in solids. Various contributions to the field Bμ in ferro- and antiferromagnetic substances are discussed. The recently reported measurements on Fe, Co, Ni, Gd, and Dy are compared, and the resulting information about the muon stopping sites and muon diffusion is presented. The μSR data in Gd allow a determination of the temperature dependence of the angle between the easy axis of magnetization and the hexagonal axis. Several models which attempt to explain the hyperfine fields at the muon by the increase of spin density due to charge screening are analyzed.

Scaling relations in magnetic, mechanical and superconducting pinning theory

Abstract The coercive field in ferromagnetic materials, the critical shear stress in alloys, and the critical current density in type-II superconductors are represented in terms of powers of the defect density, the strength and the range of the defect interaction, and of the rigidity of the domain wall, dislocation line, or flux line lattice, for the three types of material respectively. Between the exponents of these parameters general relations are valid which have to be satisfied by each detailed theory. These scaling relations hold for both, attractive and repulsive obstacles. A general rule is given on how to combine the pinning forces of different kind of obstacles.

Ferromagnetic Resonance and the Internal Field in Ferromagnetic Materials

A classical treatment of the domain energy terms of a homogeneous ferromagnetic solid leads to a formula for the internal field contributions from these terms. With this result, modifications in the resonance condition of ferromagnetic resonance arising from self energy, exchange energy, magnetocrystalline anisotropy, and applied or intrinsic stress are obtained and are applied to various crystalline anisotropy and stress conditions of interest in ferromagnetic resonance experiments. Finally, the bearing of the results on the anomalous g-values obtained in resonance experiments is considered.