SURFACE PINNING IN NIOBIUM AND A HIGH-T-C SUPERCONDUCTOR

We present magnetization-hysteresis measurements on a well annealed th in niobium sample. We observe that the magnetization hysteresis is inv ersely proportional to the applied magnetic field and the reverse magn etization is constant over a large range of the applied field; both ar e well known features associated with surface-barrier effects. We see a ''shoulder''-like structure in the hysteresis loop, This behavior is also observed in the hysteresis loops of Bi2Sr2CaCu2O8 single crystal , between 30 K and 40 K. We analyze our results of magnetization measu rements, in both niobium and Bi2Sr2CaCu2O8, in the light of the surfac e-pinning effect.