Observations of Interaction Between Magnetic Domain Wall and Grain Boundaries in Fe-3wt%Si Alloy by Kerr Microscopy
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ary pole density. Lin et al.[2] observed the interaction of the magnetic domain walls with grain boundaries and other defects during magnetization in some spinel ferrites by the Lorentz microscopy. They showed that the interaction of a domain wall with a grain boundary depended on the angle between the grain boundary plane and the domain wall, and that the pinning effect against the migration of magnetic domain walls also depended on the grain boundary segregation. Individual grain boundaries have its own character determined by the misorientation between two adjoining grains. It is well known that various physical and/or electrochemical properties (fracture strength, oxidation resistance, electrical property, etc.) depends on the grain boundary character[3-5]. Therefore, we consider that the interaction between grain boundary and magnetic domain wall should depend on the grain boundary character as well. However, there are a few investigations taking account of the grain boundary character. In this study, magnetic domain structures in polycrystalline Fe-3wt%Si alloy have been observed by a Kerr microscopy, and the effect of grain boundaries on development of magnetic domain structures was discussed. In particular, much attention has been paid to the effect of the grain boundary character on development of magnetic domain structures. Furthermore, rearrangement of magnetic domain patterns during magnetization has been observed dynamically to understand the role of grain boundaries in the magnetization process. EXPERIMENTAL PROCEDURE Specimen Preparation The material used here was a polycrystalline Fe-3wt%Si alloy, so-called "grain-oriented silicon steel" with the II10} Goss texture, in which grains were rectangular in shape along the 169 Mat. Res. Soc. Symp. Proc. Vol. 586 ©2000 Materials Research Society
rolling direction. The grain size was more than 100mm along the rolling direction and 5-50mm along the transverse direction. The thickness of the silicon steel was about 0.5mm, and grain boundary planes were placed almost normal to the surface plane. Samples suitable for a Kerr microscope observation were cut from this material using a spark cutting machine into about 25mmx10mmx0.5mm in dimension. Then, they were electropolished in a mixture of acetic acid, perchloric acid and methanol of 9 : 1 : 1 in volume to remove the surface oxide and strained layer. Grain Boundary Characterization In order to determine the orientation of each grain and to sequentially characterize individual grain boundaries included in the specimen, a scanning electron microscopy/electron back-scattered diffraction pattern (SEM/EBSD) analysis was performed. For SEM/EBSD analyses, a HITACHI S-4200 FE-SEM was used with an accelerating voltage of 40kV. Kerr Microscope Observation In this study, the magneto-optical Kerr effect was applied to observe magnetic domain structures. For observation, an OLYMPUS BX-60 optical microscope equipped with two polalizers and a mercury-vapor lamp was used. The samples were slightly coated by ferroelectric Si
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