Critical state generated by isotropic columnar defects in a Bi 2Sr 2CaCu 2O 8 single crystal

Abstract

We report magnetic relaxation studies of critical states generated by isotropic columnar defects in a Bi 2Sr 2CaCu 2O 8 single crystal. The isotropic columnar defects induce a significant enhancement of the irreversibility line and the activation energy. In the critical state, we observe a power-law time dependence of the magnetic relaxation from well below the irreversibility line. We also observe that the magnetic relaxation rate is proportional to j −1/3 at low current density and high magnetic field, and to j −1 at high current density and low magnetic field.