Investigation of the dependence of Barkhausen noise on stress and the angle between the stress and magnetization directions

The dependence of Barkhausen noise amplitude on stress, and on the angle between the stress and magnetization directions, has been investigated in specimens of AISI/SAE 4340, HY-80 and ASTM A-36 steels. In all three materials it was found that the Barkhausen noise amplitude measured with the magnetic field applied at 60° to the stress axis is independent of stress. This result is compared with the theory of elasticity which indicates that under a uniaxial or a pure bending stress, the normal component of a strain in steel is zero along the direction approximately 61° from the direction of the applied stress. It was also found that the Barkhausen noise follows the same angle dependence as that of the normal strain. These findings strongly indicate that the Barkhausen noise amplitude is directly dependent on the normal strain along the direction of the magnetization and not on the shearing strain. An explanation for such a direct normal strain dependence is given based on magnetoelastic energy. Possible application of this finding to quantitative nondestructive stress measurements is also discussed.     

Barkhausen effect in magnetic thin films: Experimental noise spectra

In this paper Barkhausen noise spectra are shown that were measured on thin uniaxial 83-17 Ni?Fe films and these spectra were compared with the known magnetic behaviour of these films. On these types of sample the Barkhausen effect had been investigated by Lambeck [1], but their Barkhausen noise spectra have not been investigated so far. The film thicknessd _m in our experiments ranged between 400 and 2400 Å. In this range a change occurs in the dynamics of the magnetization behaviour caused by transitions of the type of domain wall. The results presented here show the very strong dependence of the Barkhausen noise spectra on the type of domain wall. Films with Bloch walls always show a frequency dependence off ^?1.7 in the higher frequency range. Samples in the thickness range where the transition occurs from the Néel wall via the cross-tie wall to the Bloch wall, have exponents between ?1 and ?2. The frequencyf _c above which the measured noise intensity begins to decrease varies very much for the different films. The curve off _c versus film thicknessd _m has the same form as the curve of the domain wall mobilitym versusd _m.     

Die Temperaturabhängigkeit des magnetischen Barkhausen-Effekts IV

The size distribution of Barkhausen discontinuities (magnetic moment > 6.5 · 10^?7 cgs) of very pure nickel was measured between ?195 and 360 °C on the hysteresis loop. The mean value of internal stresses was changed in a well defined manner by stretching the specimens. For different stress values the variation with temperature of the following properties is given in diagrams: The specific number and the “mean volume”² of discontinuities, the maximal value of Barkhausen susceptibility, the mean deviation of the volume of discontinuities along the hysteresis curve, and some characteristic field strengths defined by reversible and irreversible processes. Conclusions are drawn concerning the coupling of individual wall movements composing a Barkhausen jump.     

System for controllable magnetic measurement with direct field determination

This work describes a specially designed setup for magnetic hysteresis and Barkhausen noise measurements. The setup combines two main elements: an improved fast algorithm to control the waveform of magnetic induction and simultaneous direct determination of the magnetic field. The digital feedback algorithm uses only the previous measurement cycle to correct the magnetization voltage without any additional correlation parameter; it usually converges after several tens of cycles. The magnetic field is measured at the sample surface using a vertically mounted array of sensitive Hall sensors. Linear extrapolation of the tangential field profile to the sample surface determines the true waveform of the magnetic field. This unique combination of physically based control for both parameters of the magnetization process provides stable and reliable results, which are independent of a specified experimental configuration. This is illustrated for the industrially attractive measurements of non-oriented electrical steels with a 50 Hz sinusoidal induction waveform.     

Nondestructive evaluation of isothermally annealed 12% CrMoV steel by magnetic BN measurement

The effects of microstructural evolution during isothermal annealing on structure-sensitive magnetic properties and Barkhausen noise (BN) characteristics have been investigated for 12% CrMoV steel. A rapid decrease in coercive force, remanence, hysteresis loss and hardness took place in accordance with the release of internal stresses from supersaturated martensite after annealing for only 20 minutes at 923 K. BN energy is correspondingly related with three stages of microstructural evolution such as the recovery of strain energy, the increase of precipitates size as a result of Ostwald ripening and the annihilation of dislocation density during isothermal annealing of the specimen. The linear relation between hardness and BN parameters in the magnetization region of irreversible domain wall displacement of 2.4 kA/m suggests that hardness and microstructural evolution could well be evaluated nondestructively by using BN measurements.     

Acoustic emission,domain walls and hysteresis in YIG

The acoustic emission (AE) is experimentally shown to vary along the hysteresis loop of YIG samples with the creation and/or annihilation of domain walls. The AE and the Barkhausen activities are in anticorrelation. AE and hysteresis losses are proportional, which could mean that AE is the fundamental step to convert magnetic energy into heat.     

Dependences of magnetic Barkhausen emission and magnetoacoustic emission on the microstructure of pearlitic steel

The relationships between microstructure, mechanical behaviour and magnetic properties of completely pearlitic steels have been investigated, with the objective of determining the applicability of magnetic measurements to non-destructive evaluation of the properties of high-strength pearlitic steels. High-carbon steels were heat treated to produce completely pearlitic structures with various interlamellar spacings, and their magnetic properties, including hysteresis loops, Barkhausen emission (BE) and magnetoacoustic emission (MAE) profiles, were measured. MAE profiles were found to have two peaks at the knee of hysteresis loop, while BE profiles show only a single peak at about the coercive field for all samples. The peak height ratio of the MAE profiles and the amplitude of the BE profiles increase monotonically with increasing pearlite spacing, whereas coercivity is inversely proportional to pearlite spacing. These results can be interpreted in the context of magnetic domain structures and magnetization reversal processes observed by Lorentz transmission electron microscopy, which revealed that, in specimens with smaller pearlite spacing, reverse domains nucleated and grew at higher reverse magnetic field, and domain wall jumps across cementite lamellae were smaller than in samples with coarser pearlites. The good correlation observed between the magnetic properties, mechanical strength and microstructures of these steels provides the basis for rapid and effective non-destructive assessment of their properties for industrial applications.     

Hysteresis in the behavior of a 3D ordered Josephson medium in magnetic field at a small pinning parameter

Using the approach based on analyzing variations in the configuration in the direction of the decreasing Gibbs potential, the magnetization curve for a three-dimensional ordered Josephson medium upon magnetic field cycling has been calculated for the case of a small pinning parameter. It has been demonstrated that, at any turning point, the hysteresis loop is part of some universal curve that is strictly periodic along both axes. The existence of a universal curve and its periodicity have been explained by analyzing the vortex configurations.     

Tb0.3Dy0.7Fe2合金磁畴偏转的滞回特性研究

研究了不同载荷作用下Tb_0.3Dy_0.7Fe₂合金在压磁和磁弹性效应中磁畴偏转的滞回特性. 基于Stoner-Wolhfarth模型的能量极小原理, 采用绘制自由能-磁畴偏转角度关系曲线的求解方法, 研究了压磁和磁弹性效应中载荷作用下的磁畴角度偏转和磁化过程, 计算分析了不同载荷作用下磁畴偏转的滞回特性. 研究表明, 压磁和磁弹性效应中磁畴偏转均存在明显的滞回、跃迁效应, 其中磁化强度的滞回效应来源于磁畴偏转的角度跃迁; 压磁效应中预加磁场的施加将增大磁化强度的滞回, 同时使滞回曲线向大压应力方向偏移; 磁弹性效应中磁畴偏转的滞回存在两个临界磁场强度, 不同磁场强度下合金具有不同的磁畴偏转路径和磁化滞回曲线, 临界磁场强度的大小取决于预压应力的施加. 理论分析对类磁致伸缩材料磁畴偏转模型的完善和材料器件的设计应用非常有意义.     

Visualization of the Barkhausen effect by magnetic force microscopy

By visualization of the Barkhausen effect using magnetic force microscopy we are able to provide detailed information about the physical principles that govern the magnetization reversal of a granular ferromagnetic thin film with perpendicular anisotropy. Individual Barkhausen volumes are localized and distinguished as either newly nucleated or grown by domain wall propagation. The Gaussian size distribution of nucleated Barkhausen volumes indicates an uncorrelated random process, while grown Barkhausen volumes exhibit an inverse power law distribution, which points towards a critical behavior during domain wall motion.     

Real time dynamic domain observation in bulk materials

The paper briefly reviews the development of domain observation techniques used to study basic properties of electrical steels. A new real-time, dynamic, high magnification domain observation technique is presented as an example of a state-of-the-art system, capable of imaging non-repetitive domain wall motion at power frequencies. Advantages of real-time domain observation over stroboscopic magneto-optic studies are presented and the need for real-time observations in developing future loss theories is proposed. Possible relationships between Barkhausen noise, hysteresis and non-repetitive wall motion in electrical steels are suggested and finally examples of non-repetitive wall motion in other magnetic materials are illustrated.     

隧穿磁电阻效应磁场传感器中低频噪声的测量与研究

基于隧穿磁电阻效应(TMR)的磁场传感器具有很高的磁场灵敏度, 但同时噪声也较大,有效抑制TMR磁场传感器的噪声, 尤其是低频噪声的抑制对于其在高灵敏度要求场合的应用具有重要的意义. 本文采用高精度数据采集卡搭建了噪声测量系统, 测量了全桥结构TMR磁场传感器的噪声频谱图, 发现TMR传感器的噪声在低频段表现为1/f特性, 同时噪声功率谱密度与工作电流平方成正比关系; 低频噪声在自由层翻转区间内噪声急剧增大, 证明了1/f噪声主要来源于磁噪声, 这一结果为TMR磁场传感器的噪声特性优化指明了方向.     

La0.67Pb0.33MnO3的Preisach分析

测量了居里点TC=360K的钙钛矿La0.67Pb0.33MnO3在2K关键词： Preisach模型 磁滞回线 磁化强度 磁化率     

The effect of hydrogenation on the magnetization reversal process in amorphous ferromagnets

The influence of hydrogenation and dehydrogenation on the power spectra of Barkhausen noise in amorphous alloys has been investigated. It has been shown that after hydrogenation local stress centers occur in amorphous structure. Presence of the centers leads to long-wave fluctuations of domain wall energy which cause the decrease of the number of irreversible domain wall displacements.     

Interface effect on the magnetic properties of Ni-Ge bilayer films

Magnetic and magneto-optical properties of the Ni-Ge bilayer films are studied. The unusual temperature behavior of the magnetization curves is revealed: the hysteresis loops at room temperature have a near-rectangular shape; when the films are cooled down to 4.2 K, the coercive force increases by more than an order of magnitude and the asymmetry and displacement of the loop along the field axis are observed. These effects are stronger in thinner Ni layers. The observed features are attributed to the effect of the interlayer between the Ni and Ge layers, which has a complex magnetic structure.     

Switching current noise and relaxation of ferroelectric domains

We simulate field-induced nucleation and switching of domains in a three-dimensional model of ferroelectrics with quenched disorder and varying domain sizes. We study (1) bursts of the switching current at slow driving along the hysteresis loop (electrical Barkhausen noise) and (2) the polarization reversal when a strong electric field was applied and back-switching after the field was removed. We show how these processes are related to the underlying structure of domain walls, which in turn is controlled by the pinning at quenched local electric fields. When the depolarization fields of bound charges are properly screened we find that the fractal switching current noise may appear with two distinct universal behaviors. The critical depinning of plane domain walls determines the universality class in the case of weak random fields, whereas for large randomness the massive nucleation of domains in the bulk leads to different scaling properties. In both cases the scaling exponents decay logarithmically when the driving frequency is increased. The polarization reverses in the applied field as a power-law, while its relaxation in zero field is a stretch exponential function of time. The stretching exponent depends on the strength of pinning. The results may be applicable for uniaxial relaxor ferroelectrics, such as doped SBN:Ce. Received 7 February 2002 / Received in final form 10 April 2002 Published online 9 July 2002     

Hysteresis in the de Haas-van Alphen effect

A hysteresis loop is observed for the first time in the de Haas-van Alphen (dHvA) effect of beryllium at low temperatures and quantizing magnetic field applied parallel to the hexagonal axis of the single crystal. The irreversible behavior of the magnetization occurs at the paramagnetic part of the dHvA period in conditions of Condon domain formation arising by strong enough dHvA amplitude. The resulting extremely nonlinear response to a very small modulation field offers the possibility to find in a simple way the Condon domain phase diagram. From a harmonic analysis, the shape and size of the hysteresis loop is constructed.     

Tensile stress influence on coercive properties in Fe-rich cold-drawn amorphous wires

Magnetization reversal process has been studied in ferromagnetic amorphous wires of nominal composition Fe_77.5B₁₅Si_7.5 prepared by the cold-drawing technique. Conventional hysteresis loops were measured by the fluxmetric method in the presence of the tensile stress. The measurements have been performed by short movable coils. Application of tensile stress results in increase of the remanent magnetization and decrease of the switching field. When the tensile stress is high enough, the shape of hysteresis loop is perfectly rectangular that is associated with quick enough reversals of magnetization. These hysteresis loops could be considered as quasi-magnetically bistable, but it is not exactly the standard bistability. The experiments with short movable coils have demonstrated that two domain walls (in contrast with the case of the standard bistability) propagation is responsible for the remagnetization process of the inner core.     

Unusual magnetic hysteresis behavior of oxide spinel MnCo2O4

Magnetic hysteresis behavior of the oxide spinel MnCo₂O₄ has been studied at different temperatures below its T_c≈184 K. Normal hysteresis behavior is observed down to 130 K whereas below this temperature the initial magnetization curve, at higher magnetic fields, lies outside the main loop. No related anomaly is observed in the temperature variation of magnetization or coercivity. However, the anisotropy field overcomes the coercivity below 130 K. The unusual magnetic hysteresis behavior of MnCo₂O₄, at low temperatures, may be associated with irreversible domain wall movements due to the rearrangement of the valence electrons.