Periodic magnetization instabilities in a superconducting Nb film with a square lattice of Ni dots

Abstract

Isothermal magnetization curves of a superconducting Nb film perforated by a square lattice of Ni dots exhibit quasiperiodic instabilities below \ensuremath{\sim}4 K, with a field-dependent period equal to the first, second, or third matching fields. The instabilities are found in a range of applied fields well above the saturation matching value, and under conditions where a continuous Nb film with the same dimensions and magnetization remained stable. The results suggest that terraces of matched flux density exist at the border of a flux-depleted zone created by a geometric barrier near the film edge. Geometric effects may thus play an important role in determining the presence or absence of matching effects.