AC response studying on MgB2 superconductor by Maley’s method

We have measured the imaginary susceptibility of MgB2 at different frequencies and at various dc applied magnetic fields up to 4 T. The method proposed firstly by Maley et al. on fixed applied magnetic field relaxation measurement was used to analyze the data. The information of the flux activation energy so extracted is found to be a nonlinear function of the current density, indicating a logarithmic relation U(H,J) = U-0(H) ln(J(0)/J) of the current density in this material. The dependence of the activation energy on temperature is determined by a power law U(T) proportional to (1 - (T/T-irr)(2)). The functional dependence U-0(H) proportional to H-0.8 on the applied magnetic field is determined to be in the sample. (C) 2002 Elsevier Science B.V. All rights reserved.