Flux pinning, surface and geometrical barriers in YNi₂B₂C

In the majority of the (RE)Ni₂B₂C family of superconductors (RE = Dy, Ho, Er, 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 lattice as well as the weak residual flux pinning properties. To study the residual pinning in these materials, it is, therefore, necessary to investigate the non-magnetic members such as YNi₂B₂C or LuNi₂B₂C, without the influence of magnetic order. Here, we present data from local Hall probe and global magnetization measurements used to examine flux pinning and superconducting hysteresis in YNi₂B₂C (T_c≈15.8 K). At high fields, a pronounced peak effect in the magnetization indicates that bulk pinning becomes significant as the vortex lattice softens for fields approaching B_c2. On the other hand, for small applied fields close to H_c1, direct measurements of the local induction using linear micro-Hall probe arrays show dome-like field profiles, as expected when surface and geometrical barrier effects dominate the vortex behaviour over bulk pinning. We discuss the competing roles of weak residual bulk pinning and surface and geometrical barrier effects in YNi₂B₂C.