Anomalies in vortex lattice dynamics driven by induced ac currents in superconducting films with magnetic arrays of two-fold symmetry .

A.J MORENO,; C.CHILIOTTE,; G. PASQUINI; V. BEKERIS; A. GÓMEZ, ; J. DEL VALLE,; E, M. GONZALEZ; J. L. PRIETO ; J. L. VICENT

SUPERCONDUCTOR SCIENCE AND TECHNOLOGY

IOP PUBLISHING LTD

Lugar: Londres; Año: 2015 vol. 28 p. 15001 - 15008

0953-2048

We report ac magnetic susceptibility, ac, in superconducting Nb films containing square and rectangular arrays of submicrometer magnetic Ni dots. We study the dynamics of the vortex lattice driven by the ac induced currents in the critical state regime, for T > 0.78 TC, a temperature range that is inaccessible in transport techniques. We find that matching effects for the square dot array imply highly symmetric vortex configurations, similar to the ones reported in calculations and observed in magnetotransport experiments at higher temperatures near TC . For the rectangular array we find new interesting results: pinning periodicity with field shows irregularities. Competing unstable vortex configurations could be leading to increased vortex mobility at those matching fields that induce the reconfiguration transition in transport experiments, probably related to the spatial orientation of ac induced currents relative to the rectangular pinning array. The temperature dependence of the critical current density JC(T) is analyzed for the first matching fields and we arrive to the conclusion that in the higher temperature range, pinning is related to the Ni dots high permeability, while for the lowest temperature range, where no matching features are observed, pinning by random point defects contribute.