Observation of Vortices and Columnar Defects by 1-MV Lorentz Microscopy II
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Observation of Vortices and Columnar Defects by 1-MV Lorentz Microscopy II O. Kamimura1,5,*, H. Kasai1,5, T. Matsuda1,5, K. Harada1,5, A. Tonomura1,5, S. Okayasu4, M. Sasase4, Y. Nakayama2,5, J. Shimoyama2,5, K. Kishio2,5, T. Hanaguri3,5 and K. Kitazawa3,5 1
Advanced Research Laboratory, Hitachi Ltd., Hatoyama, Saitama 350-0395, JAPAN Department of Applied Chemistry, University of Tokyo, Bunkyo, Tokyo 113-8656, JAPAN 3 Department of Advanced Materials Science, School of Frontier Science, University of Tokyo, Bunkyo, Tokyo 113-0033, JAPAN 4 Department of Material Science, Japan Atomic Energy Research Institute (JAERI), Tokai, Naka-gun, Ibaraki 319-1195, JAPAN 5 CREST, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012, JAPAN *Present address; Central Research Laboratory, Hitachi Ltd., Kokubunji, Tokyo 185-8601, JAPAN 2
ABSTRACT Two types of shape and contrast features of superconducting vortices in a Lorentz micrograph were obtained by the newly developed 1-MV field-emission transmission electron microscope on a Bi2Sr2CaCu2O8+δ (Bi-2212) thin specimen containing tilted columnar defects. The shape and contrast features could be consistently interpreted by the simulation that some vortices were pinned along tilted columnar defects and others were unpinned. The interesting property for temperature change of vortex core inside the material was also observed.
INTRODUCTION The characterization of trapping vortex at pinning centers, especially columnar defects, has been the subject of numerous studies with different experimental techniques and theoretical approaches. The information of the vortices inside a material has been inferred by measuring the macroscopic averages of pinning forces [1], the microwave magneto absorption [2] and by obtaining the microscopic positions of the vortex by two-sided Bitter decoration [3]. No means, however, are available to obtain information about whether each single vortex inside a material is actually trapped along columnar defect or not. Recently, the newly developed 1-MV field-emission electron microscope [4] allowed us to E5.14.1
observe vortices with high contrast in Bi2Sr2CaCu2O8+δ (Bi-2212) films thicker than 400 nm [5]. Here we report the successive study to obtain direct information about the vortex structure inside the material by a detailed analysis of the Lorentz images. EXPERIMENTAL Details of our experimental setup are described in the previous presentation [6].
RESULTS AND DISCUSSION Figure 1 is a typical Lorentz micrograph of superconducting vortices in Bi-2212 thin film, which was irradiated by 240-MeV Au15+ ions with the density of 5x106 ions/cm2 (BΦ = 0.1 mT), at 30 K and 0.5 mT. Each globule like black-and-white contrast corresponds to a single vortex. We noticed the vortices should be distinguished into two kinds by their contrast features, one was circular shape and higher contrast and another was elongated shape and lower contrast which was highlighted by arrows. The difference in the images can be better seen in the inset, which shows
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