Nuclear Instruments and Methods in Physics Research B40/41 (1989) 393-397 North-Holland, Amsterdam 393 zyxwvutsr SYNCHROTRON TOPOGRAPHIC STUDIES OF THE EFFECTS OF ELASTIC STRESS ON MAGNETIC DOMAIN CONFIGURATIONS IN Fe 3.5 wt.% Si SINGLE CRYSTALS M. DUDLEY Dept. of Materials Science and Engineering SUNY at Stony Brook, Stony Brook, NY I1 794, USA J. MILTAT Laboratoire de Physique des Glides, Bat. 510, UnruersitP Paris Sud, 91405, Orsay, France White beam synchrotron X-ray topography has been used to conduct in situ studies of the influence of applied elastic tensile stress on magnetic domain configurations in Fe 3.5 wt.% Si single crystals. Specimens of [Oil] tensile axis, and either (100) or (Oil) surface orientation were utilized. Tensile stress was applied using a specially designed miniature tensile stage. In specimens of (Oil) surface the characteristic Dijkstra and Martius type I structure is induced upon application of stress, eventually to be replaced by the type II structure. The transition is understandable in terms of stress-induced anisotropy. On the other hand, in specimens of (100) surface, the initial structure, which essentially consists of 90 o walls perpendicular to the tensile axis, changes to one which mainly consists of (010) and (001) 180 o walls. Both structures have approximately equal volumes magnetized along [OOl] and [OlO]. This suggests that the transition is not driven by induced anisotropy. Alternative explanations are discussed. Changes in domain configurations around inclusions are also discussed. 1. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Introduction It is well-known that X-ray topography is a tech- nique which can be used to visualize magnetic domain configurations in ferromagnetic materials. This becomes possible through the interaction of the propagating X- ray wavefields with the magnetostrictive distortions pre- sent inside crystals which have nonzero magnetostric- tion [l-6]. This capability, when combined with the general capability of the topographic technique to char- acterize the crystallographic defect content of a single crystal, affords the opportunity to study the mutual interaction between magnetic domain structures and defects. Unfortunately, when X-ray topography is con- ducted with the characteristic radiation from conven- tional sources, as is most often the case, exposure times tend to be very long, and thus prevent the possibility of dynamic studies of domain walls in motion. However, this restriction has in large part been lifted by the advent of synchrotron radiation sources, with their en- hanced brightness and subsequently short exposure times. One instance in which this enhanced capability has been used to advantage can be found in the work of Miltat [7]. In this work monochromatic synchrotron radiation topography was used to study the interaction between moving domain walls, in this case driven by applied sinusoidal magnetic fields, and growth defects. This was rendered possible by phase-locking a mechani- cal beam chopper to the sinusoidal field, enabling fixed phase topographs to be recorded; essentially a strobo- 0168-583X/89/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) scopic technique. Using this methodology, it was possi- ble to reveal the formation of instabilities in 90” do- main walls due to their interactions with dislocations - one of the fundamental justifications for hysteresis -, previously very difficult to observe directly. Another way to impart motion to domain walls in magnetostrictive crystals is to apply external stresses. Motion in such circumstances is usually driven by stress-induced anisotropy. Again, the short exposure times possible in synchrotron radiation topography make it attractive for the study of this stress-driven motion of domain walls, and the potential interactions of these moving walls with growth defects, opening up the possibility of dynamic studies [8]. Previous applica- tions of conventional source topography to such prob- lems have been largely static in nature [1,9-111. In this paper we present an abbreviated report of the results of in situ synchrotron white-beam topographic studies of such domain wall motion, and the interaction of the moving domain walls with growth defects, in single crystals of Fe 3.5 wt.% Si. A more detailed discussion of the effects of elastic stress on the overall domain configuration is to be published in a separate paper [12]. 2. Experimental Bridgman-grown single crystals of Fe 3.5 wt.% Si, in the form of - 1 mm thick discs, were purchased from II. SYNCHROTRON EXPERIMENTS