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Critical current densities and vortex dynamics in Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$ single crystals

Tamegai, Tsuyoshi*; Taen, Toshihiro*; Tsuchiya, Yuji*; Nakajima, Yasuyuki*; Okayasu, Satoru  ; Sasase, Masato*

Superconducting properties are evaluated for high-quality single crystals of Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$ in a wide range of doping levels. The critical current density, $$J$$$$_{rm c}$$, in an optimally-doped crystal (Tc $$sim$$ 24 K) shows a fishtail effect with its value over 10$$^{5}$$ A/cm$$^{2}$$ even at 5 T below 10 K. Magneto-optical imaging has clarified rather homogeneous supercurrent flow in the crystal, in spite of a large amount of impurities. In the heavy-ion irradiated sample, the presence of columnar defects are confirmed and $$J$$$$_{rm c}$$ has been enhanced by a factor of five at low temperatures, reaching 6 $$times$$ 10$$^{6}$$ A/cm$$^{2}$$ at 2 K under zero field. Flux creep rate in the heavy-ion irradiated sample has been reduced in accordance with the enhancement of $$J$$$$_{rm c}$$.



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Category:Physics, Applied



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