Effect of Periodic Artificial Flux-pinning Centers on Nb Thin Film by Lithography

Abstract

Artificial flux-pinning centers have been introduced into NbTi filaments through the drawing process for the achievement of high critical current density. We discussed periodic patterns fabricated by a lithography instead of the usual drawing process as effective artificial flux-pinning centers for practical superconductors. Periodic grooves and also lattice like holes with various depths were formed on Nb films for evaluation of the flux-pinning effect. The Nb films with 0.22μm thickness were developed on MgO (100) by electron-beam evaporation. The flux-pinning properties of the fabricated Nb films were measured by using a SQUID magnetometer. It is found that the magnetization of the fabricated Nb films increased; thus the patterns work effectually as artificial flux-pinning centers. The increase of magnetization of the film with a groove pattern was two times as large as that of the film with a hole pattern. It is explained from the effectiveness of the groove pattern for the Lorentz force. The magnetization of films with both patterns increased until fabrication depth reach half the film thickness. It is considered that this increase of magnetization is caused from an increase of elementary pinning force for each flux line.