NONLINEAR AC MAGNETIC-SUSCEPTIBILITY OF THE HIGH-TC SUPERCONDUCTOR NDBA2CU3O7

Abstract

The non-linear AC magnetic susceptibility of polycrystalline NdBa2Cu3O7 superconductor has been studied to examine the intergrain contribution to magnetic properties at low field. A superconducting sample is subjected to a DC magnetic field and a small AC magnetic field in parallel. The complicated dependence of the magnetic susceptibility on the applied field is attributed to the critical state of trapped magnetic flux in the intergrains. The non-linear magnetic susceptibility of higher harmonics with frequency up to 4f was measured as a function of varying applied fields. Numerical results of calculations using a modified critical state model are in good agreement with the measured AC susceptibility data. We find the relation J(c) approximately H(-n) (n = 2.5) for the dependence of the intergrain critical current density J(c) on the applied magnetic field H in conformity with the previous results of YBa2Cu3O7 where a smaller value of n = 1.8-2.2 was obtained.