Study of activation energy and AC-susceptibility for nano-ZnO doped MgB2 superconductor in presence of varying amplitude of applied field

Abstract

AC-susceptibility dependence of temperature measurements with varying applied magnetic field is studied for nano-ZnO doped MgB2 superconductors at different doping levels along with pristine material. The home-made susceptometer is used to measure the AC-susceptibility at different varying field (H ac = 0.2, 0.8, 4.0, 20.0 and 40.0 A/cm). The AC-susceptibility of the material shows the magnetic properties of that material either attracting or repelling in nature. The purpose of choosing the MgB2 superconductor is that because it has simple crystal structure with profound properties such as two band gaps. Generally, the AC-susceptibility has two parts, real and imaginary. The peak height of the imaginary part of the AC-susceptibilities is enhancing by increasing the applied field and shifted to the lower temperature. The real part of AC-susceptibility as a function of temperature under the presence of varying applied fields illustrates the minutely drop of the transition temperature, T c. All the samples were cooled down from 300 to 4 K in presence of applied field. The relaxation time is calculated using by optimum frequency (f = 98 Hz). The activation energy as a function of current density is measured with different doped and pure MgB2 samples. In addition, this activation energy as a function of current density is also determined under the effect of the applied field. The collective pinning model was adopted in order to calculate the activation energy as a function of current density. The current density is found to be increased as the activation energy increases in both the cases.