Flux dynamics of YBCO/Ag composite
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DC magnetization measurements have been carried out on bulk YBCO/Ag composites with silver content up to 20wt per cent. DC fields in the range 0·5 mT to 200 mT have been used to investigate the inter- and intragranular properties at 77K. The AC susceptibility as a function of temperature at different AC fields (0·026–0·30 mT) has also been studied. Under small DC fields (≈ 4 mT), depending on the Ag content andH max, the M-H loop shows a complicated behaviour. This behaviour can be explained on the basis of effect of strong field dependence of transport critical current, grain size and intragrain critical current densityJ cgm on low-field M-H loop. The estimation of intergranular critical current densityJ cjm from these loops does not remain a simple function of ΔM/d. The AC susceptibility measurements show a small increase inJ c(T) with silver content under low AC fields only, consistent with the transportJ c data; beyond thatJ c(T) decreases. This improvement inJ c(T) and transportJ c with silver can be ascribed to the improved coupling between grains but not to the pinning. Also at higher field (H max>20 mT) the addition of Ag decreases the intragrain critical current density. The upper critical field of intergranular regionH c2j and lower critical field of intragrain regionH c1g also decrease with silver content.
KeywordsFlux dynamics YBCO/Ag composite
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