Bloch Wall Motion Research Articles

Barkhausen Noise Emission in Hard-Milled Surfaces.

This paper reports on an investigation treating a hard-milled surface as a surface undergoing severe plastic deformation at elevated temperatures. This surface exhibits remarkable magnetic anisotropy (expressed in term of Barkhausen noise). This paper also shows that Barkhausen noise emission in a hard-milled surface is a function of tool wear and the corresponding microstructure transformations initiated in the tool/machined surface interface. The paper discusses the specific character of Barkhausen noise bursts and the unusually high magnitude of Barkhausen noise pulses, especially at a low degree of tool wear. The main causes can be seen in specific structures and the corresponding domain configurations formed during rapid cooling following surface heating. Domains are not randomly but preferentially oriented in the direction of the cutting speed. Barkhausen noise signals (measured in two perpendicular directions such as cutting speed and feed direction) indicate that the mechanism of Bloch wall motion during cyclic magnetization in hard-milled surfaces differs from surfaces produced by grinding cycles or the raw surface after heat treatment.

Influence of Cutting Conditions and Grinding Wheel Wear on Barkhausen Noise of Ground Surfaces

This paper is a part of the more detail research focused on the specific problems during grinding of bearing rings of diameters in the range of 600 up to 1000 mm. The paper discusses the specific aspects of surface burn after grinding associated with insufficient coolant feeding as well as the variable grinding conditions. Measurements are based on micromagnetic evaluation of ground surfaces due to large diameter of inspected rings and very fast response of the proposed technique. Magnetic inspection of parts is based of physical phenomenon originating from irreversible Bloch Wall motion well known as Barkhausen noise. Some experiments were conducted in the laboratory of our department (grinding of ring of small diameters) and specific measurements were carried out in the practice (rings of large diameters). This paper also discusses alteration of surface microhardness of ground surface as well as structure transformations.

Re-examination of the Steinmetz law for unsymmetrical magnetic hysteresis loops

We have re-examined the Steinmetz law for unsymmetrical flux-density(B)–field(H) loops in an arbitrary magnetized state for cold rolled steels from the viewpoint of magnetization mechanism. Under the criterion of B–H loops with |B|<∼ 1.1T, a relation between the hysteresis loss and flux density change was found to fall almost the same curve as that for symmetrical loops obtained conventionally. In the intermediate B regime, the relation follows the usual Steinmetz law with a power-law exponent of 1.6, whose coefficient increases with defect density. These observations demonstrate that the hysteresis loss is only the function of the flux density change and the Steinmetz law always holds true in an arbitrary magnetized state if the pinning mechanism of irreversible Bloch wall motion prevails.

Decreasing the energy loss of magnetic domain‐wall motion with nonlinear control

AbstractChaos and control of Bloch wall motion is investigated. With respect to the frequency and drive force coefficient, the movement of the magnetic domain wall is found to become unstable in the vicinity of 2 MHz and 0.2 TA/m. It is shown that unstable magnetic domain‐wall motion can be stabilized and its energy loss can be decreased by using nonlinear feedback control. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(3): 1–8, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10323

Energy Loss Decrease of Magnetic Domain-wall Motion with Nonlinear Control

Chaos and control of Bloch wall motion is investigated. As for frequency and drive force coefficient, the movement of the magnetic domain wall becomes unstable in the vicinity of 2MHz and 0.2TA/m in this thesis. It is shown that the unstable magnetic domain-wall motion is stabilized and its energy loss is decreased by using the nonlinear feedback control.

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The use of Newton’s method to solve the Landau-Lifshitz-Gilbert (LLG) equation discretized according to the Crank-Nicolson method is examined from the viewpoint of accuracy and computation time. Magnetization reversal and Bloch wall motion in a thin Permalloy film were calculated as an example. Although the convergence speed of Newton’s method is high, the solution of simultaneous algebraic equations requires a computation time of O(N3) in principle, when we denote the numbers of computing cells as N. If we take only the nearest-neighbor magnetostatic interaction into consideration in the implicit treatment, the coefficient matrix for the algebraic equation and the computation time are reduced to tridiagonal and O(N), respectively, in the case of one-dimensional calculation. Newton’s iteration can be repeated several times without increasing the order of computing time since the time required to calculate the demagnetizing field is O(N log N) if we use FFT. On detailed comparison with the Runge-Kutta method, a typical method for ordinary differential equations, the proposed method is found useful from the viewpoint of time-step dependence of numerical error and reliability.

Accuracy of the Backward-Difference Solution of the Landau–Lifshitz–Gilbert Equation

The reason for the low time-step accuracy of the previously developed approximate backward-difference solution of the Landau–Lifshitz–Gilbert (LLG) equation was found, and improved methods were developed. The improvement was carried out in two steps: correction of the expansion coefficients for the first-order backward-difference treatment of magnetization, and extension of the corrected scheme to a strict Crank–Nicolson scheme based on Newton's iteration. The time-step dependence of the velocity of a Bloch wall in planar- and perpendicular-magnetization films and the switching time of a fine iron–oxide particle were calculated to examine the time-step accuracy of the derived programs. The time-step dependence decreased considerably in the solutions obtained by the corrected program except for the Bloch wall motion in a perpendicular-magnetization film. However, it was removed almost entirely in the solutions obtained by the Crank–Nicolson method in which Newton's iteration was repeated twice per time step.

Unstable equilibrium point in chaotic domain-wall motion and Ott–Grebogi–Yorke control

A method for finding the unstable equilibrium points in Bloch wall motion is proposed, which is important for controlling the chaotic domain-wall motion by using the Ott–Grebogi–Yorke (OGY) method. The dynamics of Bloch wall motion are expressed by a nonlinear differential equation with the terms of inertia, damping, restoring, and an external magnetic drive force. An equation is transformed into the difference equations by following the OGY method, approximating linearly around an unstable equilibrium point (a saddle point), and adding a controlling input. The unstable equilibrium points are obtained by using the return map and the condition of hyperbolic fixed point. The time series of domain-wall motion successfully controlled on the unstable equilibrium points by the OGY method is shown.

Mobility of Bloch walls via the collective coordinate method

We have studied the problem of the dissipative motion of Bloch walls considering a totally anisotropic one dimensional spin chain in the presence of a magnetic field. Using the so-called "collective coordinate method" we construct an effective Hamiltonian for the Bloch wall coupled to the magnetic excitations of the system. It allows us to analyze the Brownian motion of the wall in terms of the reflection coefficient of the effective potential felt by the excitations due to the existence of the wall. We find that for finite values of the external field the wall mobility is also finite. The spectrum of the potential at large fields is investigated and the dependence of the damping constant on temperature is evaluated. As a result we find the temperature and magnetic field dependence of the wall mobility.

Theoretical approach to frequency-dependent dynamics of domain walls in magnetically ordered materials

A theoretical approach to frequency-dependent dynamics of domain walls in magnetically ordered materials is presented. To carry out this approach, we solve the phenomenological equations determining the motion of Bloch walls under the influence of a magnetic field, taking into account the effect of the relaxation of the induced magnetic anisotropy due to a redistribution of the magnetic dipoles inside the material. We use harmonic fields and we obtain that wall motion amplitude is a function of time that can both increase or decrease depending on the applied field frequency. To check these conclusions, we present the experimental results obtained via the so-called permeability disaccommodation technique in the cases of a magnetite sample and a polycrystalline yttrium-iron-garnet sample.

Crossover behavior of magnetization noise properties in disordered ferromagnets

We simulate a single 180°-Bloch wall motion driven by an external magnetic field through random impurities. The dynamics of the wall is described in terms of a Langevin-type stochastic equation of motion for the wall position, including effects of wall rigidity, quenched random impurities, external field and stray field as well as the temperature. Analyzing the temporal fluctuations of the spatially averaged wall velocity, we study the magnetization noise properties as a function of the external field. It is found that with increasing the external field the form of the noise power spectrum changes from the 1/ f-type just above the coercive field to the Lorentzian-like for large (but not huge) external fields.

Nonequilibrium Dynamics and Chaos of Domain-Wall Motion

The study of magnetic domain wall motion is important in both the field of power-magnetic microcores and in magnetic recording applications. The nonlinear differential equation for Bloch wall motion is obtained by modification of the Landau-Lifshitz-Gilbert equation. The terms of the nonlinear force of restitution and eddy current damping are added, and the equation is solved by using fourth order Runge-Kutta method. The tendency for the amplitude of magnetic domain wall motion to decrease with increasing layering frequency of the CoZrMo/SiO 2 multilayered core is well reproduced by computer simulation. The irregular oscillation of the domain wall is found to be chaotic because a fractal structure is observed in the Poincare map. This result leads to a method for investigating energy loss and irregular phenomena (error or noise in magnetic recording systems) arising from magnetic domain wall oscillations.

Chaotic oscillation of domain wall in non-equilibrium state

The nonlinear equation of the Bloch wall motion is presented by modifying the Slonczewski equation based on the Landau-Lifshitz-Gilbert equation. The nonlinear force of restitution caused by an internal stress and an eddy current damping are added. Computer simulation is performed using the fourth Runge-Kutta method. The amplitude of the domain wall oscillation in the frequency region from 50 kHz to 1 MHz is calculated and compared with the experimental values for a CoZrMo/SiO/sub 2/ multilayered core. The experimentally observed decrease of amplitude with increasing frequency is reproduced well. Using computer simulation the chaotic oscillation of a domain wall in an ideal potential well is shown to appear in spite of no randomness. Another chaotic oscillation of the domain wall with Barkhausen jumps from one potential to the neighbor is shown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

磁壁運動の非平衡動力学とカオス

The study of magnetic domain-wall motion is important in the fields of both power-magnetic micro-cores and magnetic recording applications. The nonlinear differential equation of the Bloch wall motion is obtained by modification of the Landau-Lifshitz-Gilbert equation. The terms of the non-linear force of restitution and eddy current damping are added, and the equation is solved by using the fourth Runge-Kutta method. The tendency for the amplitude of magnetic domain-wall motion to decrease with an increase in the frequency of the CoZrMo/SiO2 multilayered core is reproduced well by computer simulation. The irregular oscillation of the domain wall is found to be chaotic because a fractal structure is observed in the Poincare map. This result leads to a method for investigating energy loss and irregular phenomena (error or noise in magnetic recording systems) arising from magnetic domain-wall oscillation.

ROLE OF MICROSTRUCTURAL STATES ON THE LEVEL OF BARKHAUSEN NOISE IN PURE IRON AND LOW CARBON IRON BINARY ALLOYS

Abstract Barkhausen noise is generated by the irreversible and discontinuous motion of Bloch walls induced by an external magnetic field or a mechanical stress. These wall motions depend on the magnetic structure of the material (magnetocrystalline anisotropy for instance) and on the microstructural flaw density and distribution within the crystal. Barkhausen noise allows to characterize the microstructural state of ferromagnetic materials The aim of this work is to study the influence of various metallurgical and crystallographic parameters on the Barkhausen noise. High purity iron is studied as a reference material and is used to prepare carbon iron binary alloys (130 and 400 ppm) Characterization tests are carried out with an alternating magnetic field to reach one state of saturation to the other in the sample. The transducer used is a coil surrounding the sample. This transducer converts the variations of magnetic flow during magnetization in an electrical voltage. The signal is then amplified and filtered to record only the high frequency components. A quantitative analysis of the signal spectrum can be performed. RMS voltage is measured and provide characteristic parameters such as maximum amplitude, peak area The influence of different microstructural parameters is studied: — A pure iron sample is strained by monotonic tensile testing from 0 to 5% during loading or after unloading. Barkhausen noise is very sensitive to plastic strain an dinternal stress state, probably within the grains —Barkhausen noise depends on the carbon content as intersticial atoms and intra or intergranular iron carbides. The noise level increases slightly with the intersticial carbon content. Various aging treatments are performed to achieve £ carbide and Fe3C intragranular precipitates densities which are characterized by transmission electron microscopy observations and thermoelectric power measures. Barkhausen noise is also studied with samples in which all the carbon is precipitated as Fe3C at the grain boundaries. The Barkhausen noise level increases with the precipitation density for e carbides as well as Fe3C. Barkhausen noise also depends on precipitates coalescence. The level decreases with the degree of coalescence in the case of Fe3C precipitates The results are analyzed in terms of interaction between Bloch walls and different kinds of obstacles like crystal defects (grain boundaries, dislocation ) and precipitates (role of interfaces, mismatch stresses between precipitates and matrix, and magnetic nature of precipitates).

MONITORING FATIGUE DAMAGE IN INDUSTRIAL STEEL BY BARKHAUSEN NOISE

Abstract Barkhausen noise is generated by the rapid and irreversible motion of Bloch walls within ferromagnetic materials, when submitted to mechanical stresses or external magnetic field. Bloch walls motion is influenced by obstacles like dislocations, precipitates Therefore Barkhausen noise depends on the microstructure and the stress state of material, that can change during fatigue tests. Indeed the Barkhausen noise measurements can be used as a fatigue damage indicator when the microstructure of the fatigue specimens reaches critical configurations In the present study Barkhausen noise measurements were performed in order to detect the microstructure changes and the initiation of the damage in the case of a cyclic strained industrial steel. The sample is placed in an AC magnetic field to reach saturation. The variations of the magnetic flux within the sample are converted into electric voltage by a surrounding coil transducer. The Barkhausen noise is the high frequency component of this electric signal. The RMS voltage, is used as a quantification of the Barkhausen noise versus the applied field. A maximum in the RMS voltage of the Barkhausen noise is observed. So the RMS voltage appears as a peak shaped curve that we called the Barkhausen peak The influence of the number of cycles and the unloading mode, on the Barkhausen noise, is studied. Fatigue tests are performed according to a push-pull mode under total strain controlled conditions. After the completion of the test, the sample is magnetically characterized. Several cycle numbers (1,10,1000.) were studied to increase the damage. Four unloading modes are used: 2 in traction and 2 in compression (with no unloading plastic strain and from peak stress). The main results of this study are the following: —for given numbers of cycle, the Barkhausen peaks are very different for varying unloading modes. Moreover it is not symmetrical and it is probably depending on the sign of internal stress introduced by cyclic deformation. —for a given unloading mode a progressive boardening of the Barkhausen peak is observed as a function of the cycle number specially for an unloading mode from the tensile peak stress. Moreover a double Barkhausen peak appears from a fatigue level corresponding to approximately one thousand cycles. All these results are analyzed from the microstructural changes by cyclic deformation of the steel specially taking into account the sign and the level of the internal stress field as well as changes in the density of crystal defects, the precipitation state, and the initiation and the development of microcracks Finally characteristics of Barkhausen peaks are proposed as indicators of the fatigue damage (i.e. microcracks initiation).

Motion of a magnetic domain wall traversed by fast-rising current pulses

A Bloch wall is predicted to undergo finite displacements when traversed by a current pulse with short rise time ≤20 ns and long fall time, in thin films of metallic ferromagnets. In Ni–Fe films of thickness 85–150 nm, pulses with peak current density ≂1×107 A/cm2 are expected to induce wall displacements of order 0.1–1 μm. This effect originates from the s-d exchange interaction. It is phenomenologically similar to the well-known ‘‘wall streaming’’ motion of Bloch walls subjected to fast-rising pulses of hard-axis magnetic field. The effect is related to the existence of a novel, current-induced, term in the expression for the momentum of a magnetic domain wall.

THE PREDICTION OF POWER LOSSES IN SOFT MAGNETIC MATERIALS

Deterministic methods studying the losses due to the motion of single Bloch walls or of well defined domain structures yield equations of limited accuracy, which only provide some hints as to the trend of power losses in different materials. These results are compared with the ones obtained through a recently developed statistical treatment of the loss processes, which predicts with good precision hysteresis and dynamic losses vs. frequency and induction, on the basis of a very limited input information.

On the Radiation of Spin Waves Caused by Forced Motion of Bloch Walls in Alternating Magnetic Field

physica status solidi (b)Volume 146, Issue 1 p. K61-K63 Short Note On the Radiation of Spin Waves Caused by Forced Motion of Bloch Walls in Alternating Magnetic Field F. G. Bass, F. G. Bass Institute of Radioelectronics, Academy of Sciences of the USSR, Kharkov Search for more papers by this authorN. N. Nasonov, N. N. Nasonov Institute of Radioelectronics, Academy of Sciences of the USSR, Kharkov Search for more papers by this authorO. V. Naumenko, O. V. Naumenko Institute of Radioelectronics, Academy of Sciences of the USSR, Kharkov Search for more papers by this author F. G. Bass, F. G. Bass Institute of Radioelectronics, Academy of Sciences of the USSR, Kharkov Search for more papers by this authorN. N. Nasonov, N. N. Nasonov Institute of Radioelectronics, Academy of Sciences of the USSR, Kharkov Search for more papers by this authorO. V. Naumenko, O. V. Naumenko Institute of Radioelectronics, Academy of Sciences of the USSR, Kharkov Search for more papers by this author First published: 1 March 1988 https://doi.org/10.1002/pssb.2221460155Citations: 2 Ul. Akademika Proskury 12, SU-Kharkov-85, USSR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume146, Issue11 March 1988Pages K61-K63 RelatedInformation

The motion of head-to-head walls in orthorhombic materials

The motion of one-dimensional head-to-head walls in orthorhombic materials is investigated through numerical integration of Gilbert equation. Numerical results reveal that qualitative characteristic of head-to-head wall motion is similar to that of Bloch wall motion in uniaxial materials. Analytical solutions that reproduce numerical results very well are given. The motion of slanted walls where the normal to wall plane is slanted from the easy axis is also investigated. When the slanting angle ψ is small, the motion of slanted walls hardly differs from that of head-to-head walls. As ψ increases, however, peak velocities and low field mobilities increase significantly.