Properties Of Ferromagnetic Materials Research Articles

Math model for analysis of domain patterns stability

The paper deals with modelling of hysteresis properties of ferromagnetic materials. The simple mathematic model for analysis of domain patterns stability is presented. The domain system is described by using electrical equivalence of magnetic circuits. The results of model properties indicate the opportunity for studying the exchange coupling forces and the coercivity field distribution of elementary hysteresis structure fragments on the ferromagnetic behavior. The opportunity for studying the dynamic processes is shown.

Large systems of equations in a discrete electromagnetism: formulations and numerical algorithms

The description of discrete electromagnetic fields is achieved with the Maxwell grid equations, a set of matrix equations representing a spatial discretisation of Maxwell's equations in integral form on a dual mesh pair. Based on this matrix formalism the calculation of electromagnetic fields requires efficient techniques for the solution of commonly large, sparse systems of linear or nonlinear algebraic, differential–algebraic and ordinary differential equations. Field formulations and modern numerical-solution algorithms especially for the solution of static and quasistatic electric and magnetic fields are presented. Numerical schemes for fast-varying transient and time-harmonic current-driven or resonator electromagnetic fields are added. Details such as regularisation techniques, the modelling of motion-induced eddy currents, possible field excitation sources and the algorithmic treatment of ferromagnetic material properties are addressed. The numerical schemes include error-controlled adaptive time-domain algorithms featuring advanced extrapolation methods, linearisation methods for the nonlinear algebraic systems of equations with the possible inclusion of ferromagnetic hysteresis modelling and iterative solution methods for large sparse linear systems of equations.

Magnetization of Steel Building Materials and Structures in the Natural Geomagnetic Field

This paper presents the physical basis of the magnetic properties of ferromagnetic materials and shows their relationships with external geomagnetic field. It graphically processes the experimental data detected by an HMR magnetometer. Taking into account the natural geomagnetic field under the effects of steel U profiles, variations of the natural geomagnetic field in a steel structure building are indicated and the potential existence of Sick Building Syndrome (SBS) in these types of buildings is pointed out.

Magnetic Adaptive Testing of Non-magnetic Properties of Ferromagnetic Materials

A method of Magnetic Adaptive Testing (MAT) has been developed lately for optimized non-destructive detection and analysis of variation/degradation of non-magnetic features of ferromagnetic materials. Based on simple measurement of representative pools of magnetic hysteresis data, and on the fact that the inspected material degradation modifies the corresponding data-pools, remarkable magnetic descriptors - optimally adapted to the investigated system - can be picked up from the pools. The current experience from various tested systems showed so far that the MAT-optimized descriptors of the material degradation were always more convenient than the traditional magnetic parameters applied for the same purpose in the classical method of magnetic hysteresis non-destructive testing.

A magnetoelasticity instrument for testing the mechanical properties of ferromagnetic materials

Magnetoelasticity noise is the electromagnetic energy and sound energy released at the surface of ferromagnetic materials due to the movement of the magnetic domain walls inside the material when the material is magnetized by an alternating magnetic field. The electromagnetic energy and sound energy are released simultaneously and interact with each other. These energies carry many characteristics of the material, such as the electromagnetic character, the mechanical character, the material character, etc., and thus can be used to test these characteristics of the material. Based on this theory, an instrument for testing the stresses in ferromagnetic materials is developed in this article. The theory and the structure of the instrument are introduced. The experiment for testing the one-dimensional and two-dimensional stresses in ferromagnetic materials and the analysis of the fatigue damages are carried out. It is a portable instrument and can be used on the field. The outcomes of the test fit quite well with those obtained by the x-ray method.

Generalized magneto-optical ellipsometry in ferromagnetic metals

We present spectral generalized magneto-optical ellipsometry as an optical tool to investigate magnetic and electronic properties of ferromagnetic materials. The advantage of the simultaneous observation of the dielectric and the magnetic responses within one measurement procedure is crucial for materials with coupled degrees of freedom near a phase transition or during annealing procedures to improve the film quality by removing grain boundaries. Moreover, we show the implementation of this technique within an UHV-cryostat for a temperature range between 4.2 and 800 K and fields up to 40 mT. Examplary measurements on iron and Permalloy demonstrate the comfortable application of this technique.

Temperature-dependent spectral generalized magneto-optical ellipsometry

We present a setup for temperature-dependent spectral generalized magneto-optical ellipsometry (SGME). This technique gives access to the electronic as well as the magnetic properties of ferromagnetic materials within one single magneto-optical measurement. It also allows the determination of the orientation of the magnetization. We show spectra of the real and the imaginary part of the refractive index N as well as the magneto-optical coupling parameter Q of permalloy and iron films for in-plane magnetization. Our findings demonstrate the relevance of SGME for the understanding of the interplay between electronic and magnetic properties of ferromagnetics.

Electrons in ferromagnets with domain walls

Domain walls can significantly modify electronic properties of ferromagnetic metals. In this paper we consider theoretically the influence of domain walls on transport properties of ferromagnetic materials and the results are compared with recent experiments. In the case of diffusive transport through a thick domain wall, the semiclassical approximation is applied and a local spin transformation is performed, which replaces the system with a domain wall by the corresponding system without a domain wall but with an additional gauge field. Due to a redistribution of single-particle electron states at the wall, one obtains then either negative or positive contributions to resistivity. The situation is different for very narrow and/or constrained domain walls. In such a case, the semiclassical approximation is not valid. Instead of this the approach based on scattering matrix is applied. The domain wall then gives rise to a large positive contribution to electrical resistivity. The corresponding magnetoresistance can be therefore very large, which is in agreement with recent experiments. The limiting case of narrow domain walls in systems with a single conduction channel is analysed in detail, with the effects due to electron–electron interaction taken into account. In this particular case the magnetoresistance due to a domain wall can be extremely large.

Overview of spin transport electronics in metals

Spintronics has emerged as an exciting and dynamic field of research and development that spans numerous disciplines, including condensed matter physics, materials science, optical science and electrical engineering. The field can be divided roughly into two approaches. The first seeks to utilize the unique properties of ferromagnetic materials for novel functionality in electronic devices by incorporating a magnetic element in a device structure. This approach relies on spin-dependent transport of conduction electrons for integrating a magnetic bit state with charge-based electronic technology. Applications include magnetic field sensors incorporated as read heads and integrated, nonvolatile magnetic random-access memories. The second theme is less conventional and seeks to utilize populations of spin-polarized electrons, or individual magnetic moments, for entirely new paradigms of information processing such as quantum computing. Research in these two areas finds common ground with the study of the optical and/or electronic spin transport properties of conduction electrons. This paper will focus on relatively near term applications, represented by the first, more conventional theme, and on basic principles of spin-polarized transport.

619 第一原理計算による強磁性材料の磁気的特性およびそのひずみ依存性に関する解析

619 第一原理計算による強磁性材料の磁気的特性およびそのひずみ依存性に関する解析

Dynamic hysteresis modelling using feed-forward neural networks

A computational model for dynamic hysteresis in laminated SiFe alloys is proposed, based on feed-forward neural networks. The model employs the loss-separation property of ferromagnetic materials and combines a rate-independent hysteresis model with a correction technique for dynamic effects at each time point. The model yields accurate prediction of BH loops for arbitrary waveforms and frequencies, as they occur in electrical motors.

Magnetically Induced Potential Noise (MIPN)—A New Method for the Characterization of Magnetic Materials and for New Sensor Applications

This paper discusses a new methodology for characterizing the magnetic properties of ferromagnetic materials. The method uses an alternating electric current to periodically magnetize ferromagnetic materials. The periodic magnetization generates a high-frequency electric potential noise between two electrodes within the excitation circuit. The magnetically induced electric potential noise (MIPN) is related to the discontinuous processes that occur during magnetization similar to magnetic Barkhausen noise. This paper discusses the results of several experiments that measured both electric potential noise and Barkhausen noise signal. A comparison of the results showed that the MIPN correlates directly to magnetic Barkhausen noise. The MIPN signal is small when compared to Barkhausen noise, but it is still easy to measure under laboratory conditions. Therefore, MIPN could be an efficient technique for materials characterization and sensor technology, for example, as fiber stress sensors in a composite aircraft component.

Magnetically Induced Potential Noise (MIPN)--A New Method for the Characterization of Magnetic Materials and for New Sensor Applications

This paper discusses a new methodology for characterizing the magnetic properties of ferromagnetic materials. The method uses an alternating electric current to periodically magnetize ferromagnetic materials. The periodic magnetization generates a high-frequency electric potential noise between two electrodes within the excitation circuit. The magnetically induced electric potential noise (MIPN) is related to the discontinuous processes that occur during magnetization similar to magnetic Barkhausen noise. This paper discusses the results of several experiments that measured both electric potential noise and Barkhausen noise signal. A comparison of the results showed that the MIPN correlates directly to magnetic Barkhausen noise. The MIPN signal is small when compared to Barkhausen noise, but it is still easy to measure under laboratory conditions. Therefore, MIPN could be an efficient technique for materials characterization and sensor technology, for example, as fiber stress sensors in a composite aircraft component.

Origins of the magnetomechanical effect

A hypothesis is presented to explain the mechanism by which externally applied stresses can affect the magnetic properties of ferromagnetic materials. Experiments have revealed coincident points in the second and fourth quadrants on stressed hysteresis loops of mild steel. The results are presented along with an explanation of this effect. An atomic level theory of the origins of the magnetomechanical effect is introduced whereby spin–spin and spin–orbit coupling interact with magnetic moments to alter the magnetocrystalline anisotropy and exchange energies.

Observation of Deformation Substructure in Fatigued Intermetallic Alloys Using Magnetic Properties

ABSTRACTMagnetic properties in ferromagnetic materials are very sensitive to lattice defects such as dislocations and planar faults. Dislocation substructures and planar faults in fatigued intermetallic compounds of Ni3Fe, Fe3Al and FeAl were observed using change in magnetic properties of spontaneous magnetization and high-field susceptibility. This magnetic technique was applied for the nondestructive evaluation of fatigue life.

Microscopic foundations of the Rayleigh law of hysteresis

The hysteresis properties of ferromagnetic materials at low fields are described by the Rayleigh law. We analyze the problem in the light of modern statistical mechanics models of hysteresis. In particular, we compute the demagnetization curve and derive the Rayleigh parameters a and b in the random-field Ising model and in a model of domain wall depinning. In the random-field Ising model, the Rayleigh law is obeyed only in the disorder dominated phase, while in the low disorder phase it is not possible to demagnetize the sample. This approach allows us to link a and b to microstructural parameters, such as the domain wall energy, the internal disorder or the exchange interactions. Finally, our results are compared with experiments.

Preisach modeling of hysteresis for piezoceramic actuator system

Smart materials such as piezoceramics are being widely used as actuators and sensors to achieve micro-positioning and active control purposes. However, a major limitation of piezoceramic actuators is their lack of accuracy due to hysteresis. The Preisach model is one of the most useful models to handle hysteresis and has recently been applied to the piezoceramic material systems. Since most of the previous applications of the Preisach model are in the ferromagnetic area, the developed identification and numerical implementation approaches are based on the ferromagnetic material properties. In order to successfully model the hysteresis for piezoceramic actuator system, modifications on the identification and numerical implementation methods of the Preisach model are needed due to the differences in the hysteresis behavior between the magnetic and piezoceramic materials systems. This paper discusses the adaptation of the Preisach model to describe the hysteresis behavior of piezoceramic actuator system and presents a modified geometric interpretation and numerical implementation method for the Preisach model especially for the hysteresis modeling of piezoceramic actuator system. The demagnetized state which refers both input and output equal zero states and the generalized demagnetized state are used as the basis of Preisach model rather than the saturation states. Experiments on the hysteresis behavior of a piezoceramic actuator were carried out and the experimental measurements are compared to the hysteresis predictions. The comparison results verify the application of the modified Preisach model to piezoceramic material system.

The effect of grain boundary microstructure on Barkhausen noise in ferromagnetic materials

The Barkhausen noise (BHN) was measured in ferromagnetic materials to investigate the interaction between the grain boundary microstructure and magnetic domain walls. The grain-size effect of the BHN was studied for pure iron specimens. The Hall–Petch type relationship between the grain-size and the BHN power was found. The effect of the grain-boundary misorientation on the BHN was also studied for silicon steel specimens. The BHN power increased with increasing the grain boundary misorientation angle. It has been suggested that the arrangement of magnetic domains along a grain boundary can be affected by the grain boundary character and that hysteresis of magnetization can be optimized by controlling the grain boundary microstructure in ferromagnetic materials. The importance of understanding the behavior of magnetic domains was discussed in terms of the control of magnetic properties in ferromagnetic materials.

Computational micromagnetics:: prediction of time dependent and thermal properties

Finite element modeling treats magnetization processes on a length scale of several nanometers and thus gives a quantitative correlation between the microstructure and the magnetic properties of ferromagnetic materials. This work presents a novel finite element/boundary element micro-magnetics solver that combines a wavelet-based matrix compression technique for magnetostatic field calculations with a BDF/GMRES method for the time integration of the Gilbert equation of motion. The simulations show that metastable energy minima and nonuniform magnetic states within the grains are important factors in the reversal dynamics at finite temperature. The numerical solution of the Gilbert equation shows how reversed domains nucleate and expand. The switching time of submicron magnetic elements depends on the shape of the elements. Elements with slanted ends decrease the overall reversal time, as a transverse demagnetizing field suppresses oscillations of the magnetization. Thermal activated processes can be included adding a random thermal field to the effective magnetic field. Thermally assisted reversal was studied for CoCrPtTa thin-film media.

Magnetic Measurements of Stressed-Strained States and Remaining Service Lives of Steel Structures in Hoisting Machines and Pressurized Vessels

A technique of magnetic diagnostics has been developed on the base of correlations between physico-mechanical properties of ferromagnetic materials and their coercive force Hc. Examples of practical utilization of the technique in assessing conditions of bridge cranes and oxygen cylinders are given. By solving the inverse problem, it is possible to diagnose the stage of transition to the yield region on the base of measurements of the maximal and average coercive force, which enables one to diagnose the predestruction condition of gas cylinders. Criteria for rejecting gas cylinders based on results of statistical analysis have been established.