Fish-Tail Effect and Irreversibility Field of (Cu, C)Ba2Ca3Cu4O x -(LiF) y Superconductor
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Addition of (LiF) y ≤0.15, and of proper amount of (AgO) z =0.45–0.8 as oxidizing agent, to (Cu, C)Ba2Ca3Cu4O10+δ superconductor is useful to control and to shift the doping characteristics (hole density and distribution, and level of disorder) into the region where the irreversible properties, i.e. fish-tail effect (FTE) and irreversibility field H irr are improved. Among notable effects are the development of the second magnetization peak with a higher amplitude J c,max and the enhancement of H irr at high temperatures, above a certain value T * which depends on both y LiF and z AgO. The best results are obtained for the sample with y LiF = 0.1 and z AgO = 0.73. This sample preserves its single phase Cu, C-1234 composition. The influence on the FTE and H irr of the interplay between doping characteristics, controlled by LiF and AgO content, is discussed.
KEY WORDS:(Cu, C)Ba2Ca3Cu4O10±δ LiF-addition fish-tail effect irreversibility field high-Tc superconductor
Authors would like to thank Prof K. Togano (IMR, Tohoku University, Japan) for reading the manuscript and for allowing the use of a SQUID magnetometer and to Dr A. Crisan for continuous support of this work (NIMP, Romania). P.B. gratefully acknowledges STA/JSPS fellowship. This work was partially supported by Ministry of Education, Research and Youth, Romania under CERES program.