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Notes: After reviewing the main aspects of Barkhausen effect (BE) phenomenology and the principal theoretical models proposed for its interpretation, a new experimental and theoretical approach is presented. It is shown that definite progress in the comprehension of BE phenomenology is achieved by restricting BE experiments to the central part of the hysteresis loop, where BE behaves as a stationary stochastic process and domain wall motion is the dominant magnetization process. From the theoretical point of view, a critical reconsideration of literature results on domain wall dynamics is proposed, which leads to a Langevin equation for BE, whose solution provides definite analytic expressions for BE power spectrum and amplitude probability distribution. A comparison between the obtained theoretical predictions and typical experimental results is presented and discussed.

Notes: We report loss separation measurements performed on 1.8% SiFe nonoriented 0.2-mm laminations of variable grain size 20 μm≤s≤130 μm, in the frequency range 1 Hz≤ f≤300 Hz and peak induction range 0.7 T≤B≤1.5 T. It is shown that the excess loss behavior is well reproduced by the equation Pe =k(Bf)3/2, in agreement with a theory recently proposed by one of the authors, and the microstructural interpretation of the parameter k is discussed. The results obtained suggest that a systematic investigation of the properties of k may represent a new, promising approach to the characterization of microstructure and texture properties of nonoriented electrical steels.

Notes: Magnetic power losses have been experimentally investigated and theoretically predicted over a range of frequencies (direct current—1.5 kHz) and peak inductions (0.5–1.5 T) in 1-mm-thick FeSi 2 wt. % laminations. The direct current hysteresis properties of the system are described by the Preisach model, with the Preisach distribution function reconstructed from the measurement of the recoil magnetization curve (Bp=1.7 T). On this basis, the time behavior of the magnetic induction vs frequency at different lamination depths is calculated by a finite element method numerical solution of Maxwell equations, which takes explicitly into account the Preisach model hysteretic B(H) relationship. The computed loop shapes are, in general, in good agreement with the measured ones. The power loss dependence on frequency is predicted and experimentally found to change from a ∼f3/2 to a ∼f2 law with increasing peak induction. © 1996 American Institute of Physics.

Notes: The physical meaning of the standard Preisach model (PM) and of the Preisach distribution p(α,β), particularly for what concerns the problem of the characterization of magnetic interactions, is discussed. It is shown that the standard PM can only describe interactions having a net demagnetizing effect, and that, when the factorization p(α,β)=f(α)f(−β) holds, the simple relation Id/I∞ = 1 − 2(square root of)Ir/I∞, independent of f(x), exists between the Henkel plot remanences Ir and Id. These predictions are compared with recent experimental results. Finally, the relation between magnetic interactions and hysteresis loop shapes is discussed in the frame of a generalized moving PM, where the relation between the applied field Ha and the internal PM field H is of the form H=Ha+Hi(I), where Hi(I) is an odd function of the magnetization I. The shape of p(α,β) and of Hi(I) for nonoriented SiFe alloys is determined and analyzed.

Notes: In recent years, the Barkhausen effect has been indicated as a promising tool to investigate and verify the ideas about the self-organization of physical complex systems displaying power law distributions and 1/f noise. When measured at low magnetization rates, the Barkhausen signal displays 1/fα-type spectra (with α=1.5÷2) and power law distributions of duration and size of the Barkhausen jumps. These experimental data are quite well described by the model of Alessandro et al. which is based on a stochastic description of the domain wall dynamics over a pinning field with brownian properties. Yet, this model always predicts a 1/f 2 spectrum, and, at the moment, it is not clear if it can take into account possible effects of self-organization of the magnetization process. In order to improve the power of the model and clarify this problem, we have performed a thorough investigation of the noise spectra and the amplitude distributions of a wide set of FeCoB amorphous alloys. The stationary amplitude distribution of the signal is very well fitted by the gamma distribution P(ν)=νc−1 exp(−ν)/Γ(c), where ν is proportional to the domain wall velocity, and c is a dimensionless parameter. As predicted in Ref. , this parameter is found to have a parabolic dependence on the magnetization rate. In particular, the linear coefficient is related to the amplitude of the fluctuations of the pinning field, a parameter which can be measured directly from the power spectra. In all measured cases, the power spectra show α exponents less than 2, and thus poorly fitted by the model.Actually, the absolute value of the high frequency spectral density is not consistent with the c parameter determined from the amplitude distribution data. This discrepancy requires to introduce effects not taken into account in the model, as the propagation of the jumps along the domain wall. This highly enhances the fit of the data and indicates effects of propagation on the scale of a few millimeters. These results are analyzed in terms of new descriptions of the statistical properties of the pinning field based on fractional brownian processes. © 1996 American Institute of Physics.

Notes: Epstein-frame loss measurements were performed on 3.2% Si-Fe nonoriented strips cut along and transverse to the rolling direction, in the frequency range 10–100 Hz and at various peak inductions between 0.3 and 1.6 T. The behavior of hysteresis loss Ph and excess loss Pe vs peak induction B and frequency f was worked out and analyzed. The B dependence exhibits a rich structure, as a consequence of the coupling between magnetic domains and the grain structure. The f dependence follows the law Pe∝f3/2, in agreement with previous experiments. These results are interpreted in the frame of a generalized Preisach model recently proposed. It is shown that the excess loss dependence on B is in direct relation with that of the permeability B/H along the virgin magnetization curve. The results of numerical calculations of model predictions are presented and discussed in comparison with experimental data.

Notes: The connection between hysteresis phenomena and free energy metastable states in magnetic systems is discussed. A random free energy model is introduced, which leads to a stochastic differential equation for the evolution of magnetization in time. We show that the solutions of this equation are equivalent to the Preisach model of hysteresis. The analytical form of the Preisach distribution is calculated. © 1996 American Institute of Physics.