Microstructural and magnetic characterization in soft magnetic iron-silicon-aluminum (Sendust) alloy

Microstructure and its effect on magnetic domain structure and domain wall motion has been studied to understand the role of microstructure in determining the magnetic properties of a soft magnetic Sendust alloy. Electron microscopy of dark field imaging utilizing superlattice reflections has been mainly used to investigate the ordering behavior and corresponding microstructural changes, and Lorentz electron microscopy allowed the effect of microstructure on magnetic domain structure and wall motion to be observed. Antiphase boundaries (APBs) and other imperfections have been shown clearly and simultaneously with the observation of magnetic domain walls, even with the objective lens off.;The magnetic domain structures of the alloy in the remanent state after saturation revealed closure domains at the edge of the specimen and at cracks. Closure domains were also observed at grain boundaries, inclusions and holes. From in-situ studies of domain wall motion it was shown that the interactions of domain walls with individual dislocations and APBs are not sufficiently strong to be observed, as domain walls passed straight across them. However, grain boundaries act as strong pinning sites for domain walls, and closure domains formed at holes leading to a retardation of the domain wall motion.;Grain boundaries are shown to be the most detrimental structural defects for soft magnetic applications of the Sendust alloy. Therefore, they should preferably be removed by suitable heat treatment. For this purpose, it might be desirable to anneal the material in the single phase region to facilitate large grains but to avoid any interfacial dislocations which would be formed at interphase interfaces in the two phase field. The presence of inclusions and holes is also likely to be undesirable for soft magnetic applications of the Sendust alloy. Suggestions for improving Sendust for recording heads are therefore to have clean, non-porous alloys of very large grain size, preferable single crystal. (Abstract shortened with permission of author.)...