Flux pinning, surface and geometrical barriers in YNi2B2C

In the majority of the (RE)Ni2B2C family of superconductors (RE = Dy, Ho, E r, Tm, Y, Lu), a magnetic ordering of the RE moments (RE = Dy, Ho, Er, Tm) appears to directly influence the formation and structure of the vortex lat tice as well as the weak residual flux pinning properties. To study the res idual pinning in these materials, it is, therefore, necessary to investigat e the non-magnetic members such as YNi2B2C or LuNi2B2C, without the influen ce of magnetic order. Here, we present data from local Hall probe and globa l magnetization measurements used to examine flux pinning and superconducti ng hysteresis in YNi2B2C (T-c approximate to 15.8 K). At high fields, a pro nounced peak effect in the magnetization indicates that bulk pinning become s significant as the vortex lattice softens for fields approaching B-c2. On the other hand, for small applied fields close to H-c1, direct measurement s of the local induction using linear micro-Hall probe arrays show dome-lik e field profiles, as expected when surface and geometrical barrier effects dominate the vortex behaviour over bulk pinning. We discuss the competing r oles of weak residual bulk pinning and surface and geometrical barrier effe cts in YNi2B2C. (C) 2000 Elsevier Science B.V. All rights reserved.