Relaxation of hysteresis loop in a single crystal of YBa2Cu4O8

Magnetic relaxation has been studied for Y1Ba2Cu4O8 in order to look for changes in the relaxation rates that arise because different pinning mechanisms dominate in different magnetic field regimes. In the low field regime where the Bean-Livingston surface barrier dominates, the vortices exit on a field decreasing branch with a relaxation rate about ten times faster than they enter on a corresponding field increasing branch. In high magnetic fields where bulk pinning dominates, the relaxation rates for field increasing and field decreasing are essentially the same. (orig.)