Study of the Irreversibility Line of GdBa 2Cu 3 O 7 − δ Added with Nanosized Ferrite CoFe 2 O 4
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(CoFe 2 O 4) x GdBa 2Cu 3 O 7−δ superconducting samples were synthesized using a conventional solid-state reaction technique with 0≤x≤0.1 wt%. Characterization of the prepared samples was carried out using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The effect of adding CoFe 2 O 4 to the Gd-123 phase, which acts as a flux pinning center, was investigated by measuring the ac magnetic susceptibility at different applied dc magnetic fields. Both the superconducting transition temperature T c and the critical current density J c increased up to x=0.01 wt%, and then, they decreased with further increase in x. The temperature dependence of the irreversibility line was investigated by the logarithmic plot of the irreversibility field H irr versus (1−T irr/T c(0)). This plot shows a crossover at a field of 1000 Oe, indicating 3D to 2D flux creep fluctuations. Furthermore, the H irr–T curves are well fitted according to a theoretical model proposed by Matsushita, based on the depinning mechanism caused by thermally activated flux creep.
KeywordsGdBa 2Cu 3O7−δ Nanoferrite CoFe 2O4 ac magnetic susceptibility Irreversibility line
This work was performed in the Superconductivity and Metallic-Glass Lab, Faculty of Science, Alexandria University, Egypt, and in collaboration with SI, Physics Department at the American University of Beirut, Beirut, Lebanon.
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