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The continuous and jumpwise components of the magnetic relaxation were analyzed in the (NdDy)(FeCo)B sintered magnets in the stationary magnetic field close to the coercive field. The jumpwise magnetic relaxation of the extremely low frequency (∼0.01–0.1 Hz) and a large average amplitude (∼0.2%) of the saturation magnetization were revealed. The 2%–3% Sm doping ions increase the continuous relaxation up to 2 times and decrease the magnetization probability and average jump size down to 1.5 times. The spectral power of the magnetization jumps corresponds to the white noise appearing due to the uncorrelated individual magnetization reversal of the ∼103 independent grains. The continuous relaxation is due to the domain wall motion. Magnetic force microscopy allows us to distinguish the domain walls shift and the reversal of the grains to estimate the energy and width of the domain walls. First order reversal curve analysis revealed the contribution of the 2-14-1 phase and isolated 1-4-1 phase inclusions and the effect of Sm doping on the distribution of the switching and interaction fields of these phases. [ABSTRACT FROM AUTHOR]

Using nondestructive techniques to quantitatively estimate residual stresses along the depth is necessary to improve the ability to predict the real fatigue life of pieces for many applications. Magnetic Barkhausen noise has been proven to successfully estimate the residual stress at the surface produced by machining, plastic deformation, phase transformation or surface treatments such as shot peening, also allowing one to obtain information of the residual stress depth-profile in shot peened pieces which presented similar depth-profile shapes. However, residual stress depth-profiles with nonmonotonic or different shapes have not been successfully estimated. In the present study, an extended approach is developed in order to estimate these stresses independent of the shape of the residual stress depth-profile. The approach proposed here improves an existing model of the Barkhausen noise spectrum (Kypris-Jiles model) by adding the effect of the attenuation of the applied magnetic field on the Barkhausen noise. This extended approach is used to estimate the residual stress depth-profiles of samples with different depth-profiles using a calibration process. The approach is validated by estimating the residual stress depth-profiles, with errors smaller than 70 MPa in a depth of 130 μm, in all the samples studied. [ABSTRACT FROM AUTHOR]

The single crystal of a chiral magnet Cr1/3NbS2 exhibits discrete changes in magnetization (M) in response to changes in magnetic field (H) triggered by the formation of a chiral soliton lattice (CSL). In order to provide evidence of this phenomenon, the study of the size effect is indispensable. We investigated the effects of size on this phenomenon by the use of two single crystals, (A) and (B), whose crystal sizes along the c-axis were 110 µm and 60 µm, respectively. First, in (A), the large jumps of M observed in the process of decreasing H exhibited inconsistent features, whereas the largest and second-largest jumps in (B) exhibited reproducibility for both the value of H and the magnitude of the M jumps. This confirms that these large jumps do not originate from the Barkhausen effect, as this effect would result in M jumps appearing at random values of H. When the system size of a sample becomes smaller, the features of the Barkhausen effect are suppressed. Second, as for the successive jumps observed in the H region where the rapid change in M is entirely seen for both the samples, the number of observed M jumps for (B) is more than that for (A). Indeed, the number of the domain wall due to the 2π-soliton in the CSL increases, as the c-axis length of the single crystal increases. However, a series of M jumps must appear in a limited H region below the critical field of the order of 2 kOe. The greater the number of M jumps, the more difficult the detection of the M jump will be in the H resolution of the present setup. Thus, the effects of size on the M jumps observed in the present setup can be understood within the framework of the CSL formation. [ABSTRACT FROM AUTHOR]

The single crystal of a chiral magnet Cr1/3NbS2 exhibits discrete changes in magnetization (M) in response to changes in magnetic field (H) triggered by the formation of a chiral soliton lattice (CSL). In order to provide evidence of this phenomenon, the study of the size effect is indispensable. We investigated the effects of size on this phenomenon by the use of two single crystals, (A) and (B), whose crystal sizes along the c-axis were 110 µm and 60 µm, respectively. First, in (A), the large jumps of M observed in the process of decreasing H exhibited inconsistent features, whereas the largest and second-largest jumps in (B) exhibited reproducibility for both the value of H and the magnitude of the M jumps. This confirms that these large jumps do not originate from the Barkhausen effect, as this effect would result in M jumps appearing at random values of H. When the system size of a sample becomes smaller, the features of the Barkhausen effect are suppressed. Second, as for the successive jumps observed in the H region where the rapid change in M is entirely seen for both the samples, the number of observed M jumps for (B) is more than that for (A). Indeed, the number of the domain wall due to the 2π-soliton in the CSL increases, as the c-axis length of the single crystal increases. However, a series of M jumps must appear in a limited H region below the critical field of the order of 2 kOe. The greater the number of M jumps, the more difficult the detection of the M jump will be in the H resolution of the present setup. Thus, the effects of size on the M jumps observed in the present setup can be understood within the framework of the CSL formation. [ABSTRACT FROM AUTHOR]

A mean-field positive-feedback (PFB) theory of ferromagnetism is used to explain the origin of Barkhausen noise (BN) and to show why it is most pronounced in the irreversible regions of the hysteresis loop. By incorporating the ABBM-Sablik model of BN into the PFB theory, we obtain analytical solutions that simultaneously describe both the major hysteresis loop and, by calculating separate expressions for the differential susceptibility in the irreversible and reversible regions, the BN power response at all points of the loop. The PFB theory depends on summing components of the applied field, in particular, the non-monotonic field-magnetization relationship characterizing hysteresis, associated with physical processes occurring in the material. The resulting physical model is then validated by detailed comparisons with measured single-peak BN data in three different steels. It also agrees with the well-known influence of a demagnetizing field on the position and shape of these peaks. The results could form the basis of a physics-based method for modeling and understanding the significance of the observed single-peak (and in multi-constituent materials, multi-peak) BN envelope responses seen in contemporary applications of BN, such as quality control in manufacturing, non-destructive testing, and monitoring the microstructural state of ferromagnetic materials. [ABSTRACT FROM AUTHOR]

We derive a two parameter multi-exponential model to describe the frequency spectrum of Barkhausen noise in bulk steel under high excitation rates and applied tensile stress. We show how the amplitude and shape of the frequency spectrum depend on two directly measurable quantities, Barkhausen voltage and effective magnetic permeability, respectively, and how these change with stress. By incorporating frequency and depth dependence components into our model, we provide a framework for identifying stress variations along depth, which can be used for the purposes of nondestructive characterization. [ABSTRACT FROM AUTHOR]

Thermal Barkhausen effect is observed in poly(vinylidene fluoride/trifluoroethylene) [P(VDF-TrFE)] copolymer films for the first time. Barkhausen pulses arise at phase transition close to the Curie point during both heating and cooling without an external electric field. Three types of current pulses are obtained associated with nucleation and domain wall motion. The switched dipole number under one pulse is generally much less than 1% of the sample's total dipoles. [ABSTRACT FROM AUTHOR]

Barkhausen noise (BHN) is a voltage signal induced by a coil due to the discontinuous magnetization of ferromagnetic materials. The BHN voltage value is strongly correlated with the microstructure of such materials. In this paper, we propose a new model whereby the BHN voltage pulse width is proportional to the travel distance of the domain wall between pinning sites, and the constant of proportionality corresponds to the domain wall velocity. This correlation is examined using a model sample wherein cementite and copper precipitates as pinning sites for the domain wall were dispersed in ferrite. The test results show that the BHN voltage pulse width T and the precipitate spacing L had a proportional relationship, and that the constant of proportionality L/T grew concomitant with increases in the excitation field. The change rate of L/T with excitation field was 3.8 × 10-4 A-1 m2 sec-1, and corresponded well to the reported value that was the correlation coefficient between the domain wall velocity and the excitation field. This result demonstrates the validity of our model whereby the BHN voltage pulse is equal to the time required for the domain wall to jump over the pinning sites. [ABSTRACT FROM AUTHOR]

Magnetic Barkhausen noise (MBN) was used to characterize the progress of austenite to martensite phase transformation while cooling steel specimens, using a conventional Barkhausen noise emission setup stimulated by an alternating magnetic field. The phase transformation was also followed by electrical resistivity measurements and by optical and scanning electron microscopy. MBN measurements on a AISI D2 tool steel austenitized at 1473 K and cooled to liquid nitrogen temperature presented a clear change near 225 K during cooling, corresponding to the MS (martensite start) temperature, as confirmed by resistivity measurements. Analysis of the resulting signals suggested a novel experimental technique that measures spontaneous magnetic emission during transformation, in the absence of any external field. Spontaneous magnetic noise emission measurements were registered in situ while cooling an initially austenitic sample in liquid nitrogen, showing that local microstructural changes, corresponding to an avalanche or 'burst' phenomena, could be detected. This spontaneous magnetic emission (SME) can thus be considered a new experimental tool for the study of martensite transformations in ferrous alloys, at the same level as acoustic emission. [ABSTRACT FROM AUTHOR]

Cobalt antidot arrays defined within a Hall bar mesa have been fabricated using electron-beam lithography. The diameter of the circular antidots was fixed at 1 μm with the antidot edge-to-edge spacing varying from 2 to 0.5 μm in a square lattice and 0.4 μm in a rotated square lattice. In-plane magnetoresistance measurements were carried out to investigate the magnetization reversal properties. Antidots greatly modify the domain configuration and work as domain wall pinning sites. As a result, the switching and saturation fields increase while the magnetoresistance ratio decreases with the inclusion of antidots and also with increasing antidot areal density. Micromagnetic simulations show that the magnetization reversal of antidot arrays proceeds with the formation and annihilation of domain walls, which is manifested as Barkhausen jumps in the transition regions of the magnetoresistance curves. [ABSTRACT FROM AUTHOR]

We measured the statistical properties of Barkhausen noise in finemet films with nominal composition Fe73.5Cu1Nb3Si22.5B4 and variable thickness between 25 and 1000 nm. Films have been sputtered on glass substrates and their structure is amorphous. The critical exponents of the power-law distributions for the jumps amplitude show a remarkable stability over the whole thickness range, whereas the other macroscopic magnetic properties undergo strong variations. The value of the critical exponent is about 0.8 between 50 and 500 nm with a small increase up to 1.0 at 1000 nm. These values are similar to those observed with the same experimental technique in other two-dimensional (2D) systems, but definitely smaller with respect to the values observed in truly three-dimensional (3D) systems. Our data therefore indicate that, in the investigated thickness range, the behavior remains typical of 2D systems. The small increase of the critical exponent at 1000 nm might be an indication of a starting transition toward a 3D behavior. [ABSTRACT FROM AUTHOR]

Dual-beam high-resolution magneto-optic Kerr effect polarimetry and magnetic force microscopy (MFM) are used to study Barkhausen jumps in thin-film permalloy microstructures. Negative jumps (changes in local magnetization that oppose the drive field) are always accompanied by a nearly simultaneous positive jump, and the power-law dependence of jump-size statistical distributions of positive and negative jumps are similar. These observations, supported by sequential MFM domain images taken during field-driven reversal, indicate that negative jumps are driven by configurational changes of local domain structure associated with positive jumps that are governed by pinning, exchange, and anisotropy energies. The eddy-current coupling mechanism, that appears to account for negative jumps in bulk materials, is suppressed by sample thickness scaling in the thin-film microstructures. [ABSTRACT FROM AUTHOR]

We have performed the theoretical studies on the longitudinal dynamic magnetization process of magnetostrictive amorphous wires characterized by a large single Barkhausen jump (magnetic bistability) based on our previous experimental measurements on these wires. The domain structures of these wire samples consist of a single domain inner core with axial magnetization surrounded by the outer domain shell with the magnetization oriented perpendicular (λs>0) or circular (λs<0) to the wire axis. In the present work we use the resultant magnetization vector Mvector tilting θ angle to z axis to describe the sample’s domain structures. In terms of solving the Landau-Lifshitz-Gilbert equation followed by Mvector the analytical solution of the dimensionless axial component of the magnetization mz=MZ/Ms has been obtained, and mz[t(H0,fe),τ,γ] is a function of the field amplitude H0, field frequency fe, and the samples’ material parameters such as the damping constant τ and the gyromagnetic ratio γ. The function mz[t(H0,fe),τ,γ] allows us to study the dynamic properties of the magnetization process of a wire sample. It has been found that the switching time ts, the switching field Hsw, and the dynamic coercive field Hdc depend on a magnetic field and material parameters. We found that the parameter α=γτ/(1+τ2) related to the rate of Mvector , rotating the direction of the effective field, plays an important role in the magnetization process. By fitting the experimental data to the theoretical magnetization curve the value of the damping constant τ of the magnetostrictive amorphous wires can be estimated. [ABSTRACT FROM AUTHOR]

A detailed study of the dc hysteresis loops for current and furnace annealed amorphous wires with vanishing saturation magnetostriction constant, λs, is reported. Measurements were conducted on wires of nominal compositions (Co0.94Fe0.06)72.5Si12.5B15 and (Co0.93Fe0.07)72.5Si12.5B15 which had λs values of similar magnitude but opposite sign. The results revealed the establishment and evolution of Barkhausen jumps at different points on the major hysteresis loops. These are interpreted on the basis of the core-shell domain model, widely used in the study of amorphous magnetic wires. The control of these jumps is essential for applications of wires where magnetic noise may be an issue. The influence of annealing conditions on the coercivity and susceptibility of the wires is also reported. [ABSTRACT FROM AUTHOR]

The magnetization reversal in a thin (100 nm) Ni80Fe20/GaAs(001) film prepared by molecular-beam epitaxy has been investigated using a focused spot Kerr magnetometer. The field was sinusoidal and applied along an in-plane easy axis, with sweep rate at the coercive point in the range ∼1 kOe/s–1 MOe/s. Real time measurements of the Kerr response enabled a study of the probability distributions P(V) of the domain-wall speed as a function of sweep rate. The shape of P(V) changes from being characteristic of stochastic domain-wall motion at low sweep rate to being characteristic of quasicontinuous domain-wall motion at high sweep rate. Increasing the diameter of the focused spot from 2 to 80 μm increases the number of domain walls participating in the reversal within the probed area, which leads to an averaging effect and dulls the transition from stochastic to quasicontinuous wall motion seen in the probability distributions. [ABSTRACT FROM AUTHOR]

Evolution of Barkhausen jumps during the magnetization reversal process in disordered magnetic material is investigated. Based on the magnetoelastic effect (ΔE effect), we investigated the dynamics of Barkhausen jumps through an internal friction measurement of amorphous Fe-B-Mo ribbons. The ΔE caused by the Barkhausen jump is found to have a power-law scaling relation with the driving rate of magnetic field. Using numerical simulation, dynamics of Barkhausen avalanches in a realistic spin-lattice model for a disordered ferromagnet is analyzed. The dynamic scaling and inhomogeneous behavior observed in both experiments and theoretical models are presented and discussed. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the origin of magnetic easy axis in pipeline steel using an angular magnetic Barkhausen noise (MBN) technique. Application of angular MBN to monitor magnetic anisotropy; Experimental technique; Results and discussion; Conclusions.

Presents information on a study on the Barkhausen noise amplitude. Mechanical stress situations with biaxial characters; Methodology used in conducting the study; Results of the study.

Presents a study which investigated the stress-dependent magnetic easy axis in steel with the use of magnetic Barkhausen noise. Analysis of stress effects on single iron crystals; Experimental technique; Results and discussion.

Focuses on a study which investigated the angular dependence of surface magnetic Barkhausen noise on eight different samples of oriented silicon-iron steel laminate. Theory; Experimental technique; Results; Discussion; Conclusion.

Presents a study that discussed the effect of mechanical stress on a Barkhausen noise signal integrated across a cycle of ramped magnetic field. Apparatus block diagram showing the interrelationships between the measurement configuration and the processed signals; Experimental Barkhausen data for XC10 French steel at various stress levels; Tabulation of hysteresis loss and Barkhausen noise amplitude integrated across H, as obtained experimentally for XC10 French steel.

Focuses on a study which examined magnetization processes at low field in nonmagnetoresistive amorphous ribbons treated by current annealing. Description of the domain structure of the region; Discussion on the behavior of the critical field; Influence of the applied tensile stress on the critical field; Factors that help determine the large Barkhausen jump process.

Investigates the angular dependence of magnetic Barkhausen noise (MBN) on eight surfaces through the thickness of a manganese steel pipeline. Effect of the application of a varying magnetic field on the magnetization of a ferromagnetic material; Result of processing steps associated with the manufacture of pipeline steels; Experimental details and result of the study.

Presents a study which investigated the Barkhausen effect (BE) in metallic ferromagnetic systems by a Langevin description of the stochastic motion of a domain wall in a randomly perturbed medium. Calculation of BE statistical properties; Description of the model used; Probability amplitude distribution.

Presents a study which investigated the Barkhausen effect (BE) phenomenology in iron-based ferromagnetic alloys. Statistical properties of BE; Experimental procedures used; Results on amplitude probability distribution.

Presents an experimental and theoretical approach for the phenomenology and interpretation of the Barkhausen effect (BE) in ferromagnetic materials. Proof of the existence of magnetic domains; Usual setup employed in BE experiments; Step by step procedure of a theoretical framework for BE interpretation.

The effects of design parameters for optimizing the performance of sensors for magnetic Barkhausen emission measurement are presented. This study was performed using finite element analysis. The design parameters investigated include core material, core-tip curvature, core length, and pole spacing. Considering a combination of permeability and saturation magnetization, iron was selected as the core material among other materials investigated. Although a flat core-tipwould result in higher magnetic flux concentration in the test specimen, a curved core-tip is preferred. The sensor-to-specimen coupling is thereby improved especially for materials with different surface geometries. Smaller pole spacing resulted in higher flux concentration. [ABSTRACT FROM AUTHOR]

The paper deals with assessment of microstress state of martensite P91 steel using three complementary techniques: mechanical Barkhausen emission, magnetoacoustic emission (MAE), and X-ray diffraction (XRD) profile analysis. Magnetic coercivity Hc and microstructure were investigated with inductive magnetometry and magnetic force microscopy (MFM), respectively. Internal stress level of P91 steel was modified by heat treatment. Steel samples were austenitized, quenched, and then tempered at three temperatures (720 °C, 750 °C, and 780 °C) during increasing time (from 15min up to 240min). The microstrain level ei was evaluated using Williamson-Hall method. It was revealed that during tempering microstrain systematically decreases from ϵi=2.5 x10-1 for as quenched state down to ϵi=0.3x10-3 for well tempered samples. Both mechanical hardness (Vicker's HV) and magnetic hardness (coercivity) decrease almost linearly with decreasing microstrain while the MAE and MBE intensities strongly increase. Tempering leads to evident shift of the MeBN intensity maximum recorded for the first load towards lower applied strain values and to increase of MAE intensity. This indicates that the microstress state deduced by magnetic techniques is correlated with microstrains evaluated with XRD technique. [ABSTRACT FROM AUTHOR]

In this study, we conceptually divided a ferromagnetic specimen into layers along its depth. For each layer, we derived a non-linear integral equation that describes the attenuation with frequency and distance of magnetic Barkhausen emissions coming from that layer. We postulate that the Barkhausen spectrum measured at the surface by an induction coil can be expressed as the sum of the individual layer spectra. We show how a non-linear least squares algorithm can be used to recover the properties in individual layers. These are related to stress using an extension to the theory of ferromagnetic hysteresis. We found that the quality of the fit is influenced by the sensitivity of the ferromagnetic material to strain, as well as by the sensor-specimen coupling. The proposed method can be used for the non-destructive characterization of stress as a function of depth in magnetic materials. [ABSTRACT FROM AUTHOR]

Artificial vortex core pinning sites are induced in thin Permalloy disks by point exposure to as few as 10 000 ions from a focused Ga+ beam. These pinning sites yield a first-order change in the magnetization response of the disk. A single site can keep the vortex core pinned over an applied field range comparable to the vortex annihilation field of the unaltered disk. Several widely separated sites can work together to keep the core pinned in one place, while the Barkhausen effect is eliminated from the magnetization curve over a range approaching the saturation moment of the disk. [ABSTRACT FROM AUTHOR]

The variation in magnetic properties of a Fe-1%Cu model alloy due to a cold rolling and a thermal aging has been evaluated to simulate the radiation damage of reactor pressure vessel of nuclear power plant. The thermal aging was conducted at 500 °C with different aging times in series. The hysteresis loops, magnetic Barkhausen noise (BN) and Vickers microhardness were measured for prestrained, strained, and thermal aged samples. The coercivity increased by a plastic strain and decreased by thermal aging, The BN decreased in the prestrained and strained samples but large changes were observed in the strained sample. These results were interpreted in terms of the domain wall motion signified by a change in the mean free path associated with microinternal stress and copper rich precipitates. [ABSTRACT FROM AUTHOR]

Precipitates in the form of grain growth inhibitors play an essential role in the production of grain-oriented electrical steels, as they promote the development of Goss texture during secondary recrystallization. However, the presence of precipitates in the final material can have a detrimental effect on loss and permeability, as they impede domain wall motion during the magnetization process. In previous work [K. Jenkins and M. Lindenmo, J. Magn. Magn. Mater. 320, 2423 (2008)], a conventional grain-oriented electrical steel was presented that contained very fine precipitates, which did not damage the bulk magnetic properties. In this article the influence of precipitate size is investigated by comparing local Barkhausen noise measurements and electron backscatter diffraction analysis for a number of grain-oriented electrical steels, which are metallurgically similar except for the size and abundance of precipitates. [ABSTRACT FROM AUTHOR]

Nearly zero magnetostrictive microwires have been proven to be very versatile, due to their extremely soft magnetic properties, the changes in their magnetization mechanism with dimensions, and the appearance of sensitive application-related effects, such as the large Barkhausen and the giant magnetoimpedance effects. Their sensitive magnetoimpedance response originates in the specific domain structure, composed of an inner core and an outer shell (OS), since the OS with a circumferential easy axis is the main region involved in the magnetoimpedance effect. The circumferential OS is believed to display a bamboolike structure with consecutive rings circumferentially magnetized in opposite directions. However, earlier theoretical studies predicted a uniformly magnetized OS as being energetically favored. This paper aims to clarify this contradiction. The variation of the magnetostatic energy from the bamboo domain to the uniformly magnetized state has been calculated and it has been found to be null. Therefore, a uniformly magnetized OS has lower energy due to the absence of domain walls. Calculation results are supported by magneto-optical Kerr effect surface domain images and surface hysteresis loops. For large values of the metallic nucleus diameter, as well as for microwires with the glass coating removed, the OS vanishes, being replaced with a surface region with helical magnetization, which expands toward the microwire surface. [ABSTRACT FROM AUTHOR]

The effects of varying shot peening process parameters on drag force signatures are examined. The salient features of such signatures are found to compare favorably with those expected from consideration of the effects of peening on magnetic properties combined with analysis of the actual force sources. The potential utility of the drag force method for automatic assessment of peening quality and uniformity is encouraged by experimental results. [ABSTRACT FROM AUTHOR]

The one-dimensional Barkhausen effect was observed in lithographically defined magnetic strips of Co/Pd multilayer films. The magnetic domain expanded stepwise with a constant speed between pinning sites. Both the wall propagation and the pinning were characterized by the thermal activation process based on their exponential dependency on the strength of the applied magnetic field. The Barkhausen volume was determined to be 1.7×10-13 cm3, which was several orders larger than the activation volume of the wall propagation, 6.5×10-18 cm3. [ABSTRACT FROM AUTHOR]

The effects of microstructural variations with depth on Barkhausen effect (BE) signals in surface-modified ferrous materials have been studied through measurements and simulations based on a hysteretic-stochastic model. The BE signals measured from an unhardened sample show a peak near zero field. In contrast, the BE signals in surface-hardened samples with different case depths exhibit low-amplitude pulses near zero field and a peak at a high reverse field, which are attributed to irreversible magnetization processes in the soft core and the hardened surface layer, respectively. Theoretical analysis showed that the model parameters k and ξ, which describe the domain-wall pinning strength and the range of interaction of a domain wall with pinning sites, respectively, are related to each other as ξ=a ρ-1/2=b/k via the pinning site density ρ, where a and b are constants. The relationship was used to simulate BE signals of the surface-hardened samples as a sum of signals generated at different depths by taking into account signal attenuation due to eddy current shielding. The simulated results were found to exhibit the general features observed in the experimental results. [ABSTRACT FROM AUTHOR]

We investigate the statistical distribution of separation time ΔT between the adjacent two Barkhausen jumps in Co films having the thickness ranging from 5 to 50 nm. By means of a magneto-optical microscope magnetometer, we determine the time-dependent magnetization curve and the separation time ΔT between two jump events during avalanche process from the directly observed time-resolved domain evolution patterns. Through a statistical analysis of ΔT, we find that the distribution P(ΔT) seems to follow a power-law behavior with the same form within the error range, irrespective of the film thickness. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We develop an experimental technique for direct, full-field, time-resolved observation of the Barkhausen avalanche in a two-dimensional thin-film system, using a magneto-optical microscope magnetometer (MOMM). Real-time visualization capability of the MOMM enables us to microscopically observe all the details of the Barkhausen avalanche in Co thin films, which is not feasible using other indirect experimental techniques adopted so far. We find that there exist fluctuating flexible domain walls deformed by defects and that, interestingly enough, the domain wall exhibits still-detectable fluctuation even around a strong linear defect as well as a strong point-like defect, from which we conclude that a critical avalanche continues to exist even in strong pinning cases. [ABSTRACT FROM AUTHOR]

Unlike the case of an oscillating magnetic field, power losses in a magnetic material eventually start decreasing as the magnitude of a rotating field increases. In some hysteresis models, the loss increases monotonically as the magnitude of a rotating field increases. The simplified vector Preisach model and the reduced vector Preisach model do not suffer from this error. For magnetization-dependent reversible models, such as the Della Torre-Oti-Kadar, and for state-dependent models such as the complete moving model, the loss per cycle has two components. The first is computed from the Preisach integrals, and the second is computed from the change in the stored energy in the reversible component. It is noted that the latter loss can occur even if there are no Barkhausen jumps. This article discusses the details of how the model accomplishes this. [ABSTRACT FROM AUTHOR]

The magnetic response of a ferromagnetically ordered perovskite La[SUB0.7]Sr[SUB03]MnO[SUB3] with a critical temperature T[SUBC]=325 K has been measured as a function of applied field h[SUBa] over the interval -4 kOe &les; h[SUBa] &les; + 4 kOe, and as a function of temperature T over the interval 5 K &les; T &les; 350 K which spans the ordered phase, and analyzed within the framework of a model which reduces all magnetic systems to an ensemble of temperature dependent, asymmetric double well subsystems. The model is able to replicate the field and temperature dependence of the measured zero field cooled moment, the field cooled moment, the isothermal remanent moment, the thermoremanent moment, the initial magnetizing curve, the magnetizing remanence, the major hysteresis loop, and the demagnetizing remanence, and yields the spectrum of double well dissipation barriers and level splittings which represent the Barkhausen excitations between metastable domain configurations. [ABSTRACT FROM AUTHOR]

The magnetic behavior of partially electrostatic discharge (ESD) damaged giant magnetoresistive (GMR) heads during thermal and bias current stress is studied. Heads were ESD damaged to a level that would still pass quasistatic specifications and then monitored while at a higher temperature (100 °C or 150 °C) and bias current (5 to 6 mA) for up to 40 h. While controls showed no early changes, significant changes in amplitude, asymmetry, and Barkhausen jump were seen within the first hour of stressing in 10% of the partially ESD damaged heads. Heads that experienced pinned layer reversal or developed Barkhausen jumps were especially prone to large changes in magnetic response during stressing. It is concluded that some partially ESD damaged GMR heads can exhibit spontaneous and large degradation in amplitude and magnetic stability during high thermal and bias current stressing. [ABSTRACT FROM AUTHOR]

Grain oriented Fe 3.5% Si sheet samples with a Goss (GO) microstructure and Fe 3.5% samples with nonoriented (NO) grains were tested using two Barkhausen effects, the classical Barkhausen effect (HBE) and the mechanical Barkhausen effect (MBE), as well as the magnetoacoustic emission (MAE). The aim of the work was to present further evidence that the B(H) hysteresis with effects like HBE and MAE, and magnetomechanical hysteresis with MBE are correlated via internal stress barriers pinning domain walls (DWs). In the case of a GO alloy, the long axis of the sample was parallel to the [100], [110], and [111] directions with respect to the rolling direction. The HBE and MAE were measured using a C-core electromagnet supplied with a triangular wave form of current intensity. The MBE intensity was recorded during a monotonous increase of shear stress using a torque machine. The maxima of MBE intensity for the "first load" mode for a NO sample and for three GO samples indicate an internal stress distribution pinning 90° DWs. The MAE plots reveal at least two maxima which are well correlated with H strength values where creation and annihilation of magnetic domains appears. Since the MBE and MAE are associated with abrupt jumps of 90° DW, the existence of MBE and MAE reinforces the fact that such DWs are present in the tested samples. These walls belong mainly to the secondary closure domains at GO alloys and to closure domains at NO alloy. [ABSTRACT FROM AUTHOR]

A relationship between the parameters of a hysteretic-stochastic process model of the Barkhausen effect (BE) and the microstructural features of a series of ferritic/pearlitic steel samples has been identified. The root-mean-square values and pulse height distributions of the experimental and modeled BE signals showed similar dependence on the pearlite content. The correlation length parameter ξ of the model, which represents the range of interaction of domain walls with pinning sites, was found to obey ξ = AV[sub f]D[sub f] + BV[sub p]D[sub p] where V[sub f](V[sub p]) and D[sub f](D[sub p]) are the volume fraction and grain size of ferrite (pearlite). [ABSTRACT FROM AUTHOR]

In this work, Barkhausen noise measurements are shown for a series of amorphous ribbons: Metglas 2605TCA, Metglas 2705M, and Finemet materials with composition Fe[sub 73.5]Cu[sub 1]Nb[sub 3]Si[sub 18.5]B[sub 4] under different stress (σ) and annealing temperature (T[sub A]) conditions. The dynamical state of the system is characterized by the power spectra and amplitude distribution functions as well as by the Minkowski-Bouligand dimension for each set of samples. Special attention has been paid to the ranges of vanishing anisotropies: low applied stress for the Metglas samples and the nanocrystallized phase of Finemet materials. [ABSTRACT FROM AUTHOR]

Reports the development of a magnetic easy axis in a steel plate sample using a magnetic Barkhausen noise (MBN) technique. Influence of the cold bending process on axial magnetic easy axis; Evolution of the easy axis; Effect of residual hoop compression on the MBN signal.

The Barkhausen model of Alessandro et al. [J. Appl. Phys. 68, 2901 (1990)] has been extended to nonstationary domain wall dynamics. The assumptions of the original model limit, its use to situations where the differential permeability, and time derivative of applied field are constant. The later model of Jiles et al. assumes that the Barkhausen activity in a given time interval is proportional to the rate of change of irreversible magnetization which can be calculated from hysteresis models. The extended model presented here incorporates ideas from both of these. It assumes that the pinning field and domain wall velocity behave according to the Alessandro model, but allows the rate of change of the magnetic flux to vary around a moving average which is determined by the shape of the hysteresis curve and the applied magnetic field wave form. As a result, the new model allows for changes in permeability with applied field and can also reproduce the frequency response of experimental Barkhausen signals. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of microstructural changes on magnetic Barkhausen noise (BN) and magnetomechanical acoustic emission (MAE) in Mn–Mo–Ni pressure-vessel steel with various microstructures was investigated. The BN and MAE signals were strongly influenced by the microstructural features which were characterized by transmission electron micrograph observation. BN energy and the measured area under the rectified signal envelope varied inversely with hardness, and changed with the microstructure. It indicates that they are closely related to the dislocation density and residual stress which act as a barrier to irreversible domain wall motion. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

By using a model for giant magnetoresistance (GMR) hysteresis and a model for Barkhausen noise, a magnetic hysteresis model is used to map the effects of magnetic hysteresis on GMR and on accompanying magnetic noise in a GMR magnetic field sensor. Two magnetic noise sources potentially exist in the field sensor: (1) the GMR multilayer material and (2) permalloy field concentrators. The GMR material typically shows a coercivity at H[sub c]≅1 kA/m, much larger than H[sub c]=0.012 kA/m of permalloy. Because permalloy has a very large maximum permeability, it is a much larger magnetic noise source than the GMR material, and would greatly affect sensor operation if operated near H=0. By operating with a bias field well above 1 kA/m, one can operate away from both noise sources. Because the increasing and decreasing arms of the magnetic hysteresis tail of the GMR material are each approximately proportional to |H|[sup 1/2] over a large field range, the model shows that increasing and decreasing portions of the GMR vs H hysteresis curve turn out to be linear, parallel to each other, for the operating field region. If the GMR curve is linear in a region away from H[sub c], a bias field operation in this range would mean that the sensor would not only be nearly noiseless (save for Johnson noise) but also would exhibit linear change in field under an applied field H and could easily be calibrated to measure H. Thus, the modeling points the way to low noise GMR field sensor design. In practice, it is found that biasing at fields halfway down the GMR curve does indeed produce a much quieter measurement than near zero bias field. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Results concerning linear variable differential transformer (LVDT) displacement measurements using Fe[sub 77.5]Si[sub 7.5]B[sub 15] amorphous wires as movable core are presented. Taking advantage of the large Barkhausen (LBE) effect in amorphous wire, a small exciting field and a small number of windings in the secondary coils are necessary to get an large output signal of the LVDT. The thermal noise of the output becomes low, due to the small number of coil turns, increasing thus the sensitivity of the LVDT. The results obtained show a linear dependence of the LVDT response on the displacement of the moving core for displacements up to about 14 mm, with accuracy of 1 μm. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We show that the Barkhausen avalanches exhibit power law distributions and scaling exponents belonging to two distinct universality classes. We explain these results in terms of the critical behavior of the domain wall at the depinning transition, with exponents set by the long-range dipolar interactions arising from local magnetostatic fields, and by the elastic curvature of the wall. We are also able to predict the precise dependence of the cutoff on the demagnetizing factor k due to sample size. These predictions are experimentally confirmed on three samples (two polycrystalline 6.5 wt % Si–Fe and an amorphous Fe[sub 21]Co[sub 64]B[sub 15] under applied tensile stress) which are progressively cut in order to increase k. All these results allow us to link the material microstructure and the sample geometry to the macroscopic noise properties. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]