The profiles of the magnetic induction near the surface of cylindrical niobium samples were measured by the method of differential susceptibility in minor hysteresis loops. The flux density gradient near the surface generally is considerably higher than in the bulk. This may be interpreted in terms of a surface barrier or of a surface pinning force. The experimental results can be summarized as follows: (1) Surface pinning always increased with surface roughness.(2) When the surface was polished the barrier was only observed in a plastically deformed sample. (3) The influence of the surface seems to extend down to a depth of some tenth of a millimeter.
The flux density gradient in a plastically deformed niobium single crystal was measured. The profiles in increasing and decreasing field are not symmetric, and depend on the history of the magnetic field. This effect was observed up to 0.9Hc2, although it was more pronounced at lower fields. These results, as well as an observed asymmetry of minor hysteresis loops, cannot be understood by the critical state model. We suggest that they are related to the creation of dislocations in the flux line lattice.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.