Quantitative evaluation of Barkhausen jumps according to the signals of magnetoacoustic emission
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QUANTITATIVE EVALUATION OF BARKHAUSEN JUMPS ACCORDING TO THE SIGNALS OF MAGNETOACOUSTIC EMISSION V. R. Skal’s’kyi,1 O. M. Serhienko,1, 2 V. B. Mykhal’chuk,1 and R. I. Semehenivs’kyi 1
UDC 537.634: 620.179.17
We propose an analytic model for the quantitative assessment of a volume jump of domain walls, caused by the Barkhausen effect, under the action of a magnetic field accompanied by magnetoelastic acoustic emission. Dependences for the evaluation of its amplitudes are constructed. Initial data for the calculation of displacements with the proposed model are obtained. It is shown that the method of magnetoelastic acoustic emission is sensitive to the reconstruction of the domain structure of ferromagnets. Keywords: magnetoacoustic emission, Barkhausen effect, domains, magnetization, magnetostriction.
The radiation of elastic waves caused by the Barkhausen effect (BE) or magnetoacoustic emission (MAE) is connected with magnetostriction strains in local regions of a ferromagnet and sudden changes of locations of domain walls under the influence of an external magnetic field [1 – 4]. Magnetoacoustic emission has been investigated less thoroughly than the BE. Phenomenological approaches to the explanation of the features of MAE were considered earlier [3, 5, 6]. They take into account the motion of domain boundaries and the formation and growth of nuclei of reversal magnetization. Most experiments have been performed on polycrystalline steel samples [3, 5 – 11], nickel, Armco-iron, silicon iron, and iron–nickel alloys [5, 12 – 15]. For this purpose, resonance transducers of acoustic emission (AE) with a dynamic mode of reversal magnetization of samples of alloys in the frequency range 20 – 100 Hz were used. The rate of counting and the amplitude of a MAE signal depending on the amplitude of the field of reversal magnetization, external mechanical stresses, annealing temperature, hardness, sizes of inclusions, and distance between them were recorded [8, 15]. It has been established that a MAE signal increases as tensile stresses decrease and as the grain size increases (excluding nickel, in which a MAE signal, on the contrary, decreases). In many cases, for polycrystalline materials, the rate of counting, by contrast, increases as external tensile forces rise. Moreover, experiments show that MAE arises predominantly during stepwise motion of domain boundaries where the magnetization vectors are noncollinear [1, 2, 16]. Modeling of MAE Signals Caused by Jumps of Domain Walls The aim of the work is to develop a computational model for evaluating maximum elastic displacements in a ferromagnetic material during Barkhausen jumps and check it experimentally. To analyze the components of the vector of displacements and then MAE signals caused by jumps of domain walls as a result of BE, we assume that a certain volume of the body, namely, the volume in which jumps 1 Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. 2 Corresponding author; e-mail: [email protected].
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