LOW FIELD MAGNETIC-RELAXATION PHENOMENA IN YBACUO

The relaxation of the magnetization of a sintered sample of YBa2Cu3O7 has been investigated in a SQUID-magnetometer The relaxation may adequately be described by a power law t-a at all fields (1-100 gauss) and temperatures (20-90 K) investigated. A marked field dependence of the exponent a and a corresponding field dependence in the relaxation rate (1/H &partM/&partln t) is observed. Three rather distinct field regimes with different values of the exponent a and different field dependences of the relaxation rate may be distinguished: a low field region where a logarithmic relaxation (a0) is found, an intermediate regime with a0.04 and a high field region with a0.07.