Long Time Power Law Magnetic Relaxation in Detwinned YBa2Cu3O7-δ Single Crystals

The time-dependent magnetic relaxation was measured in a full field penetrated YBa2Cu3O7-δ detwinned crystal for long times up to 5x105 sec. The relaxation data exhibit a power-law time dependence over a wide range of temperatures and magnetic fields indicative of flux creep with logarithmic dependence of the effective creep activation barrier U(J). A theoretical model is employed to analyze the data and to determine the activation energy.