Precision measurement of magnetic relaxation in YBa2Cu3O7: Power-law versus logarithmic decay

Using a sensitive, micrometer-sized, scanning Hall probe, we have made precision measurements of the relaxation of the remanent magnetization in single crystal YBa2Cu3O7. The technique allows us to determine how the relaxation rate varies over the face of the crystal. At all temperatures from 4.2 to 74 K, the relaxation is observed to follow a power-law dependence B(1+t/)-1/, instead of logarithmic behavior. We discuss the origin of, and compare the relaxation behavior with recent calculations of vortex diffusion.