Evidence for the interaction between magnetic domain walls and dislocations in high-purity iron from magnetomechanical damping experiments

Abstract

The magnetomechanical damping, when plotted as a function of the amplitude of an alternative shear strain, exhibits a maximum, from which it is possible to deduce the effective internal stress opposed to the motion of 90° magnetic domain walls. High‐purity specimens of iron are strained up to 3% at room temperature, and from the variation of internal strain with applied stress it is shown that the effective internal stress is proportional to the square root of dislocation density. During further straining at 77K, the interaction between 90° magnetic domain walls and dislocation tangles is evidenced: the dislocation density inside the tangles decreases together with the effective internal stress, while the mobility of magnetic domain walls increases. The dislocation density inside the tangles is calculated for the sample prestrained 3% at room temperature from the values of the effective internal stress.

Two phase modeling of the influence of plastic strain on the magnetic and magnetostrictive behaviors of ferromagnetic materials

“…It is assumed though this description that the kinematic hardening is only linked to the interphase heterogeneities. Yield functions for both phases are: (14) s i , σ yi and R i are respectively the deviatoric tensor, yield strength and isotropic hardening of phase i.…”

“…Plastic strain leads to strong non linear changes in the magnetic behavior [1,14,15,16,17]. Experiments performed with various carbon steels [18,19,20,21,22,23], electrical steels [16,17,24,25], iron-cobalt [26,27] or nickel alloys [1] have shown that the degradation occurs at the early stages of plastic strain [28,29].…”

“…Figure 1 illustrates, for instance, the strong change of magnetic and magnetostrictive behavior of a common iron-silicon electrical steel submitted to a very low plastic strain after a tensile test [30]. The influence of plastic deformation on the magnetic state has been studied by many authors, some of them interested by physical mechanisms at the local scale [32,33,14], the others looking at the influence of cutting (and associated plasticity) on the global response of an electrical machine [34,35,36]. Interactions between the magnetic microstructure (magnetic domains and walls) and the mechanical microstructure (dislocations, grains, stress fields) are the basis of the phenomenon.…”

Detection of Magnetomechanical Effect in Structural Steel Using GMR 2nd Order Gradiometer Based Sensors

“…The dislocations produced into the material by the plastic deformation interact and multiply through the crystal lattice, and as a consequence they interact with the magnetic domain wall influencing the magnetic structure and properties of the ferromagnetic materials. The plastic strains are non-linearly coupled with magnetic properties in the case of steels [1]. The experimental tests carried out both on carbon and electrical steels have highlighted that the influence exerted by plastic strains on material magnetic responses is stronger at the early stages of the deformation process and generally leads to a degradation of the material behaviour, since magnetic losses increased and permeability decreased.…”

“…This strong coupling is due to some mechanisms acting on the local scale. More specifically, the interactions between the magnetic microstructure (magnetic domains and walls) and the mechanical microstructure (dislocations, grains, stress fields) are the basis of the phenomenon [1,3]. The common accepted approach is considering microstructural defects generated by the plastic slips process as pinning centres for domain walls motion [4].…”