The penetration of magnetic flux into a thin superconducting film of Nb3Sn
with critical temperature 17.8K and critical current density 6MA/cm^2 was
visualized using magneto-optical imaging. Below 8 K an avalanche-like flux
penetration in form of big and branching dendritic structures was observed in
response to increasing perpendicular applied field. When a growing dendritic
branch meets a linear defect in the film, several scenarios were observed: the
branch can turn and propagate along the defect, continue propagation right
through it, or "tunnel" along a flux-filled defect and continue growth from its
other end. The avalanches manifest themselves in numerous small and random
jumps found in the magnetization curve.Comment: 3 pages, 4 figures, submitted to Cryogenics. Revision: M(H) data
adde
Flux distributions in thin superconducting NbN films placed in a
perpendicular magnetic field have been studied using magneto-optical imaging.
Below 5.5 K the flux penetrates in the form of abrupt avalanches resulting in
dendritic structures. Magnetization curves in this regime exhibit extremely
noisy behavior. Stability is restored both above a threshold temperature T* and
applied field H*, where H* is smaller for increasing field than during descent.
The dendrite size and morphology are strongly T dependent, and fractal analysis
of the first dendrites entering into a virgin film shows that dendrites formed
at higher T have larger fractal dimension.Comment: 3 pages, 5 figure
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.