PINNING EFFECTS BY ARRAYS OF MAGNETIC DOTS ON NIOBIUM FILM

The interaction between an ordered array of submicron magnetic particl es and a superconducting thin film can lead to important pinning effec ts due to the synchronized interaction with the vortex lattice. Triang ular and square lattices of submicrometer magnetic dots have been fabr icated by electron beam lithography, with typical spacings in the rang e 400-600 nm and dot radius around 100-200 nm. The influence of these lattices of small particles on the superconducting properties of niobi um films has been studied. The resistivity vs. magnetic field curves e xhibit a series of sharp regular minima close to the transition temper ature. These minima appear at integer multiples of the matching held, which is determined by the lattice parameter of the dot array, thus, r evealing a synchronized pinning effect due to the magnetic dots. (C) 1 998 Elsevier Science B.V. All rights reserved.