Rotational Magnetization Process Research Articles

Model of a 3D Magnetic Permeability Tensor Considering Rotation and Saturation States in Materials with Axial Anisotropy.

The paper proposes a 3D extension of the linear tensor model of magnetic permeability for axially anisotropic materials. In the proposed model, all phases of a magnetization process are considered: linear magnetization, magnetization rotation, and magnetic saturation. The model of the magnetization rotation process is based on the analyses of both anisotropic energy and magnetostatic energy, which directly connect the proposed description with physical phenomena occurring during a magnetization process. The proposed model was validated on the base of previously presented experimental characteristics. The presented extension of the tensor description of magnetic permeability enables the modelling of inductive devices with cores made of anisotropic magnetic materials and the modelling of magnetic cores subjected to mechanical stresses. It is especially suitable for finite element modelling of the devices working in a magnetic saturation state, such as fluxgate sensors.

Numerical simulations of vector hysteresis processes via the Preisach model and the Energy Based Model: An application to Fe-Si laminated alloys

The paper presents the state of the art and the problems already open in modelling the hysteresis phenomenon in 2-D for laminated soft ferromagnetic materials. Firstly, a thorough experimental investigation has been carried out at a very low frequency by a single disk tester (SDT) for a specimen of innovative NGO electrical steel sheet. Scalar, rotational and elliptic magnetization processes have been experimentally measured under controlled waveforms of the magnetic induction vector thanks to an effective digital feedback algorithm. Two numerical model of hysteresis have been taken into account to reproduce the measured magnetization processes: the vector Preisach model (VPM) and the Energy Based Model (EBM). The main advantages and limitations in the use of the two hysteresis models are comprehensively analysed and discussed, taking into consideration both the problem of identification and the simulation results. In particular, the effective capability of the models to reproduce the vector field trajectories and to predict the hysteresis power losses has been shown. Conclusive considerations involve the memory usage and the computational time for the low level of abstraction implementation of the two hysteresis models.

Linear magnetic field dependence of the magnetodielectric effect in eutectic BaTiO3-CoFe2O4 multiferroic material fabricated by containerless processing

To maximize the formation of an anisotropic interface between the magnetostrictive phase and the electrostrictive phase, a eutectic BaTiO3-CoFe2O4 multiferroic material is fabricated by containerless processing. The composites in this process had a fine eutectic structure, especially at a eutectic composition of BaTiO3:CoFe2O4 = 62:38. TEM observations revealed that the (1 0 0) plane of tetragonal BaTiO3 and the (1 0 0) plane of CoFe2O4 were oriented in parallel. In addition to the largest magnetodielectric effect in the eutectic-composition samples, we confirmed the permittivity is controlled linearly by applying a high magnetic field through forced magnetostriction. So far, the peak of the magnetodielectric effect around 0.25 T has been only found in the sintered CoFe2O4 polycrystalline sample. Thus, the containerless processing provides us a route to produce an ideal microstructure without accompanying 90° domain wall process and rotational magnetization process, which enhances the magnetodielectric effect.

Magnetization Processes in Ribbons of Soft Magnetic Amorphous Alloys

Using iron-based (Fe–B–Si–C; Fe–Ni–Si–B) and cobalt-based (Co–Fe–Ni–Cr–Mn–Si–B) soft magnetic alloys as examples, we have studied the dependences of the remanence measured using minor hysteresis loops on the maximum induction. The different degrees of stabilization of the 180° and 90° domain walls allows these dependences to be used to analyze the magnetization processes that occur in the rapidly quenched soft magnetic alloys. It has been established from the Br(Bm) dependences that, in the ribbons of soft magnetic amorphous alloys, the processes of the rotation of the magnetization oriented perpendicular to the ribbon plane start before the end of the processes of the displacement of the walls of domains with planar magnetization. After the end of the magnetization rotation processes, the magnetization processes can be interpreted as the displacement of the domain walls with a planar magnetization accompanied by a decrease in their number and a transition to a bistable state.

Implementation of the Single Hysteron Model in a Finite-Element Scheme

The single hysteron model is identified to reconstruct the magnetization processes of a grain-oriented electrical steel and it is implemented in a finite-element scheme. The model involves the Zeeman energy and the anisotropy energy of the material and an interaction field to take into account others terms, such as the magnetoelastic energy, the exchange energy, inclusions, and crystallographic discontinuities. The interaction field is evaluated experimentally using a round rotational single sheet tester, where a disk sample of the material is excited for several rotational magnetization processes. Details about the finite-element scheme, the computational time, and the memory allocations involved in the simulations are presented and discussed.

A comprehensive complex permeability approach to soft magnetic bulk cores from pure or resin coated Fe and pulverized alloys at elevated temperatures

Soft magnetic bulk materials prepared by the consolidation of Fe powders and pulverized amorphous and nanocrystalline alloys based on Fe and Co in pure state or blended with polymeric resins are investigated by complex permeability approach at temperatures from 25 °C to 110 °C. A wide scale of variations in complex permeability dispersion ascribed to domain walls and magnetization rotation processes versus magnetizing frequency and temperature is obtained. The observed universal behavior in such types of bulk magnets is reasonably predicted in terms of permeability dispersion model of overall magnetization process assuming more or less broad and asymmetric distribution of relaxation times. It is found that permeability spectra vary smoothly with temperature and various scenarios of magneto-thermal behavior are observed and explained. The reconstruction of corresponding relaxation times distribution functions profiles versus temperature reveals that temperature slightly affects the dynamic properties of magnetic moments in bulk powder materials and such influence results in a broadening of relaxation times distribution.

Effects of diamagnetic Ga dilution on the Faraday response of bismuth-doped iron garnet films

In bismuth-doped iron garnets, diamagnetic dilution of Fe with Ga is a well-known method to increase the Faraday rotation response under externally applied magnetic fields. It is found, however, that while this method improves responsivity at larger field strengths, the responsivity under smaller fields (which are more typical in sensing applications) is generally unaffected by Ga doping. The data indicate that the low-field responsivity is limited by anomalous pinning effects in the rotational magnetization process of the ferromagnetic domains. To overcome this, a magnetic biasing technique was developed, which enhances responsivity by activating Barkhausen steps in the films to free the domains from their pinning sites.

Magnetoelastic Sensor Studies on Amorphous Magnetic FeSiB Wire and the Application in Viscosity Measurement

In this work, possible use of FeSiB amorphous magnetic wire as a magnetoelastic sensor was investigated. As-received wire did not show any magnetoelastic change. But, the wire annealed in a furnace at 465 ∘C for various times showed good magnetoelastic change. A very large change in the resonance frequency of annealed FeSiB wire as a function of DC magnetic field was obtained. This large change was explained on the basis of the high value of magnetostriction of FeSiB wire and the increase in the rotational magnetization process. It was also found that resonance frequency of FeSiB wire changes when the wire was in a liquid with different viscosities.

CoFe/MnIr 박막 재료에서 저자장 마이크로파 흡수 특성 분석

본 연구에서는 교환 결합력을 갖는 CoFe/MnIr 박막 재료에서 강자성 공명 장치를 이용하여 자기장 방향에 따른 저자장 마이크로파 흡수(Low field microwave absorption, LFMA) 및 강자성 공명 신호를 측정하였다. 낮은 자기장 영역에서 나타나는 LFMA 신호는 자구의 회전 밀접하게 관계됨을 자화 곡선으로부터 알 수 있었다. 이러한 LFMA 신호 특성을 분석하기 위하여 강자성 공명 신호로부터 측정한 교환 바이어스(<TEX>$H_{ex}$</TEX> = 58.5 Oe) 및 일축 이방성 자기장(<TEX>$H_k$</TEX> = 30Oe)을 S-W model에 적용하여 자화과정의 횡방향 자화량(transverse magnetization, <TEX>$M_{\tau}$</TEX>) 및 투자율(transverse susceptibility, <TEX>${\mu}_{\tau}$</TEX>)을 계산하였다. 자화 곤란축에서 측정된 LFMA 신호는 <TEX>$M_{\tau}$</TEX> 비례하는 경향을 보였지만, 자화 곤란축과 수직 방향으로 접근하면 <TEX>$M_{\tau}$</TEX> 및 <TEX>${\mu}_{\tau}$</TEX> 모두에 의존하는 특성을 보였다. We measured the low field microwave absorption (LFMA) and ferromagnetic resonance (FMR) signals at various magnetic field angle in exchange biased CoFe/MnIr thin film. The LFMA signals were dominantly related to the magnetization rotation process. In order to analyze the LFMA signal, we calculated transverse magnetization (<TEX>$M_{\tau}$</TEX>) and permeability (<TEX>${\mu}_{\tau}$</TEX>) for CoFe/MnIr thin film by using S-W model, which magnetic parameters of exchange bias (<TEX>$H_{ex}$</TEX> = 58.5 Oe) and uniaxial anisotropy field (<TEX>$H_k$</TEX> = 30Oe) was obtained from FMR signals. The LFMA signal at hard axis showed similar behavior compared with that of <TEX>$M_{\tau}$</TEX>. As the magnetic field angle approach to the perpendicular to hard axis, the LFMA signals were depending on both of <TEX>$M_{\tau}$</TEX> and <TEX>${\mu}_{\tau}$</TEX>.

Magnetically correlated anisotropic resistive switching manipulated by electric field in Co/PMN-PT heterostructures

The nonvolatile behaviors of magnetically correlated anisotropic resistive switching in Co/0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (Co/PMN-PT) multiferroic heterostructures are systematically investigated. When the polarization state of PMN-PT is reversed, a non-volatile anisotropic resistivity switch occurs, corresponding to the non-volatile 90°-rotation of magnetic-easy-axis in Co film owing to the competition between magnetoelastic and interfacial anisotropies. The anisotropic magnetoresistivities (AMR) between two opposite polarization states in a field below anisotropic field also show a 90° phase-shift. While at fields above anisotropic field, the AMR reveals the asymmetric cos2(θ)-like behaviors. The AMR manipulated by electric and magnetic fields is of benefit for studying the magnetization rotation processes.

Influence of simplifications of the rotational magnetization model on calculation accuracy

Purpose – The purpose of this paper is to present the differences in results of numerical calculations arising from different simplifications of the rotational magnetization model in typical dynamo sheets. Design/methodology/approach – A comprehensive model of rotational magnetization processes in typical dynamo sheets should take into consideration the magnetic hysteresis and eddy current phenomena and also certain anisotropic properties. The chosen model of the rotational magnetization is briefly presented in this paper. A method of the inclusion of the rotational magnetization model into equations of the magnetic field distribution is described. The correctness of these equations has been verified experimentally. Numerical calculations of the rotational magnetization in two types of dynamo sheets were carried out for several simplifications of the described model. Findings – Results of numerical calculations of the rotational magnetization with the omission of the hysteresis phenomenon or with the omis...

Exchange bias field induced symmetry-breaking of magnetization rotation in two-dimension

We investigate the effect of strain-induced intrinsic exchange bias field (HEB) on the magnetization rotation process in a nominally “single” layered La2/3Sr1/3MnO3 (LSMO) film. The intrinsic exchange bias appears when the LSMO film is grown on LaAlO3 substrate. The HEB is proved to be an effective approach to tuning the in-plane magnetization rotation, producing a 360° instead of 180° periodicity in the anisotropic magnetoresistance curves measured in a low external magnetic field. The planar Hall effect curves are asymmetric when the in-plane magnetization rotate between two orthogonal axes of LSMO, helped or hindered by the HEB. Our study reveals that the HEB in but not limited to LSMO with phase separation exhibits an unprecedentedly two-dimensional effect rather than merely establishing a reference magnetization direction as achieved in ferromagnetic/antiferromagnetic bilayers, thus furthering the cognition of manipulating the magnetization orientation.

Enhancing GMI properties of melt-extracted Co-based amorphous wires by twin-zone Joule annealing

The influence of twin-zone Joule annealing (TJA) on the microstructure and magnetic properties of melt-extracted Co68.2Fe4.3B15Si12.5 amorphous microwires has been investigated. Experimental results indicated that twin-zone Joule annealing treatment improved the GMI property of as-cast wires to a greater extent comparing with Joule annealing (JA) and conventional vacuum annealing (CVA) techniques. At 15MHz, e.g., the maximum GMI ratio [ΔZ/Z0]max of a TJA wire increases to 104.29%, which is more than 5 times of 20.49% for the as-cast wire, nearly two times of 56.47% for the JA wire, while the CVA wire has a decreased GMI ratio; the field response sensitivity of the TJA wire increased to 171.62%/Oe from 80.32%/Oe for the as-cast wire, exceeding the values of 140.76%/Oe for the JA wire and of 39.17%/Oe for the CVA wire. The stress or structural relaxation in TJA wire increases circumferential permeability, and magnetic moment achieves a critical state of excitation for overcoming eddy-current damping or “nail-sticked” action in rotational magnetization process at relatively high frequency. From the microstructural point of view, the role of regularly arranged atomic micro-regions (RAAM) and of medium range order region (MROR) determines the efficiency of various annealing techniques. Conclusively, TJA is established as an efficient annealing technique to enhance the GMI effect of wires, which can subsequently be used for detecting weak magnetic field at relatively wider working range (±2.0Oe).

Modelling of rotational magnetization in anisotropic sheets

PurposeThe aim of this paper is to present a new relatively simple model of the rotational magnetization process in anisotropic sheets.Design/methodology/approachThe surface of a sample of an anisotropic sheet is divided into an assumed number of specified directions. To each direction a certain hysteresis loop, the so‐called direction hysteresis, is assigned. The parameters of the proposed model are calculated on the basis of such values as the saturation flux density, the residual flux density (remanence), and the coercive force. It is also necessary to take into account the anisotropy constant and also the distribution function of the grains in the sample of the given anisotropic material.FindingsThe model of the rotational magnetization process of soft ferromagnetic materials takes into account two fundamental phenomena: the irreversible domain wall movements and the rotations of the flux density vectors from the easy magnetization axes. This model can also be used for the modelling of the axial magnetization process.Practical implicationsThe proposed model can be used in numerical calculations of the rotational magnetization in magnetic circuits of electrical machines for any work conditions. However, for the comprehensive calculation of the magnetic field distribution this model should be completed with eddy current equations. Eddy currents influence magnetic field distribution in electric steel sheets.Originality/valueA new model of the rotational magnetization process in anisotropic sheets is proposed.

Improvement of Integration-Type Dynamic E&amp;S Modeling

This paper presents an improved integral-type E&S modeling for applications under high magnetic flux density conditions. In the conventional integral-type dynamic E&S modeling, we assumed linear increment of higher harmonic components including in the magnetic field strength waveforms versus the magnetic flux density. However the higher harmonic components decrease after getting a peak value in rotational magnetization process around saturation region (1.6T – 1.8T). Improvement of the integral-type dynamic E&S modeling for the high magnetic flux conditions was investigated in comparison with the measured one and verification with a simple problem was demonstrated in this paper.

Fluxmetric-magnetooptical approach to broadband energy losses in amorphous ribbons

The magnetization process in field annealed amorphous ribbons has been investigated from dc to 10 MHz. Loss and permeability measurements, carried out both on single strips and ring samples by means of a broadband fluxmetric setup, have been associated with observations of the domain wall dynamics by high-speed stroboscopic Kerr apparatus. Transverse anisotropy Co-based ribbons exhibit a combination of rotational and domain wall processes, the latter being observed to progressively damp with frequency and coming to a halt on approaching the megahertz range. Given the vanishing direct contribution of the domain walls to the high-frequency magnetization process, the so-called classical loss formulation, associated with the rotational magnetization processes, is expected to correspondingly hold for the energy loss W(f). Under these conditions, W(f) tends to increase linearly with f, which, in view of the expected surge of the skin effect, does not agree with the f1/2 behavior accordingly predicted by standard formulas. This points to the specific properties of the rotational process and the role played by the exchange torque in connection with incomplete flux penetration.

Magnetization reversal processes of single nanomagnets and their energy barrier

Micromagnetic simulations were performed to investigate the influence of geometry and magnetic anisotropy constant on energy barrier and magnetization reversal mechanism of individual bits important for the bit patterned media concept in magnetic data storage. It is shown that dependency of the energy barrier on magnetic and geometric properties of bits can be described by an analytical approach in the case of quasi-coherent magnetization rotation process. However, when the bit size exceeds a critical size, for which an incoherent magnetization reversal is preferred, the analytical approach becomes invalid and no self-consistent theory is available. By systematically investigating the influence of bit size on the magnetization reversal mode, it was found that the transition from quasi-coherent to incoherent magnetization reversal mode can still be described analytically if an activation volume is considered instead of the bit volume. In this case, the nucleation volume is an important parameter determining thermal stability of the bit. If the volume of the bit is larger than twice the activation volume, the energy barrier stays nearly constant; with further increase in bit size, no gain in thermal stability can be achieved.

Micromagnetic Analysis of Shielded Write Heads Using Symmetric Multiprocessing Systems

Acceleration of micromagnetic calculations on symmetric multiprocessing (SMP) systems is investigated. A speed up of more than 20 times has been realized compared with the serial processing software. The SMP system with the optimized software has a speed up of 5.6 times compared to a previous version on an 8-CPU cluster system. Micromagnetic analysis of a write head with trailing and side shields is performed to derive the quasi-static recording field distributions, dynamic recording fields and magnetization rotation processes. It is noted that the dynamic recording field is affected by the trailing and side shields. A write head for shingled recording is also analyzed and is found to be promising due to its higher recording field.

Kerr microscopy study of magnetization reversal in uniaxial Co-films

Abstract We have studied the magnetization reversal of uniaxial Co(1 0 1 0) films as a function of the applied field orientation by means of magneto-optical Kerr effect microscopy. Hereby, we find that while stable intermediate domain states exist for most field directions, their occurrence is suppressed for field orientations along the easy axis of magnetization. To facilitate this study, we have developed a data extraction methodology that allows for the quantitative analysis and compact display of entire magnetization distribution field-sequences in a single picture. It furthermore allows for the automated data analysis to unambiguously distinguish magnetization rotation processes from field-induced domain formation.

Modeling of Magnetic Domain in Grain-Oriented Electrical Steel Sheets based on Multi-directional Magnetostriction Measurements

In this paper, a novel magnetic domain model on grain-oriented electrical steel was established which is based on magnetostriction measurements for an interpretation of the magnetization behavior under rotational magnetization process. The novel model has brought about useful insights for understanding on reconstruction of magnetic domain and kinetics of magnetic domain wall.