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  • Author: Jozef Pal’a x
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Abstract

The magnetic Barkhausen noise (MBN) measurement technique is a popular magnetic method used for non destructive detection of microstructural changes in ferromagnetic materials. The MBN parameters depend on the gap between the excitation yoke and measured object. To suppress the negative influence of lift off, we tried to find a parameter of the MBN, which could be independent of lift off changing in a practical range. The lift off effect was analysed experimentally on construction steel samples with various levels of carbon content. We found that the amplitude distribution is a promising parameter of MBN in this regard. Measurement results showed that the slope of amplitude distribution was roughly independent of lift off.

Abstract

The magnetic Barkhausen noise (MBN) measurement method is a widely used non-destructive evaluation technique used for inspection of ferromagnetic materials. Besides other influences, the excitation yoke lift-off is a significant issue of this method deteriorating the measurement accuracy. In this paper, the lift-off effect is analysed mainly on grain oriented Fe-3%Si steel subjected to various heat treatment conditions. Based on investigation of relationship between the amplitude distribution of MBN and lift-off, an approach to suppress the lift-off effect is proposed. Proposed approach utilizes the digital feedback optimising the measurement based on the amplitude distribution of MBN. The results demonstrated that the approach can highly suppress the lift-off effect up to 2 mm.

Abstract

The metamagnetic properties of the manganese magnesium ferrites having the general formula Mn0.7Mg0.3Fe2O4 prepared by the standard ceramic technique have been studied. It is proposed that when a change of temperature at adequate magnetic field is applied in a Mn0.7Mg0.3Fe2O4 a magnetic phase transition will be generated, giving rise to an antiferromagnetic (AFM) state from ferrimagnetic (FM) phase. The critical transition field H ac = 300 A/m was estimated for critical magnetization curve of transition from the metamagnetic behavior to FM behavior of sample. The FM to AFM transition in these ferrites is accompanied by a Néel type to Yafet-Kittel type transition and gradual spin ordering changes of the unit cell volume. The application of an external magnetic field to the low-temperatures AFM state causes the sample to reset to the original FM state.