Relaxation effects in high<i>T</i>_csuperconductors

Abstract

The relaxation of the isothermal d.c. magnetization M in zero-field cooled Ba-La-Cu-O and Sr-La-Cu-O specimens has been investigated at temperatures T ≪ Tc in magnetic fields 0 ⩽ H < 400 Oe. The results show that the value of M changes logarithmically with time following the law M ∝ lm (t/t0) with great accuracy over an observation time of 50 000 s. At H = 0, the relaxation rate of the remanent magnetization ∂M/∂ ln t increases with temperature and with the third power of the field to which the specimen has been previously cycled.