Physica C: Superconductivity and its applications

The temperature- and field-dependent activation energy of a proton irradiated YBCO single crystal

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We have investigated the separate temperature and field dependences of the activation energy U(T, H, J) for pinning of magnetic flux in a high-Jc, proton irradiated Y1Ba2Cu3O7-δ single crystal. The work achieves two objectives: (1) to clarify arguments concerning the "anomalous" rise of U with increasing temperature and (2) to resolve differences in magnitude of U found when comparing magnetic relaxation and resistivity results. The temperature and field dependences of U for fixed J were first obtained by extrapolating U(J) as observed in magnetic relaxation (flux creep) experiments to lower J. For fixed current density J, peaks in U were observed with respect to both temperature and magnetic field. For H > 2T, U(H) varied as ∼H-α, with α depending on temperature and current. The attempt time, treated as a fitting parameter, lies near 10-3∼10-2s in most cases. The magnitude of U agrees well with values reported from resistivity studies on high-Jc epitaxial films. © 1992 Elsevier Science Publishers B.V. All rights reserved.