The flux pinning of a 120 nm thick polycrystalline niobium film has be
en investigated dynamically with the vibrating reed technique and, sta
tically, with torque magnetometry. Weakly temperature dependent maxima
were observed by torque magnetometry consistent with the matching fie
lds for formation and splitting of vortex chains. From these measureme
nts, we have determined the volume pinning force as a function of appl
ied field which shows a non-monotonic behavior compatible with differe
nt vortex regimes. We found that the formation and splitting of vortex
chains has negligible influence on the elastic coupling of the vortex
lattice measured with the vibrating reed. Both techniques showed shar
p maxima in the angular dependence of the upper critical field in agre
ement with the appearance of surface superconductivity. The elastic co
upling between flux lines and film as well as the energy dissipation a
re finite at magnetic fields higher than the bulk critical field B-c2
suggesting the existence of a vortex structure in this field region. (
C) 1998 Elsevier Science B.V. All rights reserved.