Magneto-optical study of grain boundaries, interfaces and grain boundary networks in YBaCuO
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1 Magneto-optical study of grain boundaries, interfaces and grain boundary networks in YBaCuO Ch. Jooss1 , L.-O. Kautschor1 , M.P. Delamare1 , B. Bringmann2 , K. Guth1 , V. Born1 S. Sievers1 , H. Walter2, J. Dzick2 , J. Ho mann2 , H. C. Freyhardt1;2 , B. de Boer3 , B. Holzapfel3 and F. Sandiumenge4 4
1 Institut fur Materialphysik, University of Gottingen, Germany 2 Zentrum fur Funktionswerksto e, Gottingen, Germany 3 IFW Dresden, Institute of metallic materials, Germany
Institut de Ciencia de Materials, Universitat Autonoma de Barcelona, Catalonia, Spain
Abstract
Using quantitative magneto-optics and an inversion scheme of Biot-Savart's law the local current carrying capability of various types of grain boundaries (GB's) and interfaces in YBaCuO thin lms and bulk material was investigated. In all GB's and interfaces a spatial variation of the local critical current density j was observed which, however, has di erent reasons, such as microstructural inhomogeneities, magnetic eld dependence of j and size e ects in extended GB's and networks of low angle grain boundaries (LAGB's). c
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Introduction
The depression of the intergrain critical current density at grain boundaries has been widely documented in di erently processed YBaCuO materials [1, 2, 3, 4]. The critical current density j () through grain boundaries (GB's) is very sensitive to the orientation of the adjacent grains and strongly decreases with the misorientation angle [2, 5, 6] for > , where denotes a critical angle. In YBCO thin- lm bicrystals grown on SrTiO3 substrates, Æ Æ an exponential decrease of the upper limit of j () for > 3 5 is observed. Simultaneously, the j data for a xed scatters signi cantly. In melt-textured grown (MTG) bicrystals or bicrystals grown by liquid phase epitaxy (LPE), a di erent angular dependence of j () is observed [6, 7], where the decrease of j with increasing is smaller than in thin lm GB's. However, the j in the GB's in bulk materials never exceeds the upper limit of j () which is measured in thin- lm bicrystals. From these results, the question is risen, if the critical current density through GB's and interfaces does not only depend on intrinsic properties: The grain misorientation , the related dislocation structure at LAGB's [8], the related structural units at high angle grain boundaries [9], or the structural width at antiphase boundaries [10, 11], respectively. The transport properties seem to depend also on extrinsic properties, in particular, on magnetic
ux dependent vortex pinning at di erent material's defects in and outside GB's and on secondary phases [12]. Also, depending on the magnitude of external magnetic eld or the self elds of the currents, the j through GB's may be in uenced by magnetic coupling of intergranular vortices to the stronger pinned intragranular vortices. In this contribution, the local critical current density of di erently grown GB's and interfaces in YBCO is investigated by magneto-optical (MO) measurements and inversion of Biot-Savart's law for the determi
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