Driven vortex lattices have been studied in Nb films, in which natural random pinning coexists with artificial ordered arrays of defects ͑submicrometric Ni dots͒. Three different dynamic regimes are found: for low vortex velocities, there is a plastic flow regime in which random defects frustrate the effect of the ordered array; then, for vortex velocities in the range 1-100 m/s, there is a sudden increase in the interaction between the vortex lattice and the ordered dot array, associated to the onset of quasi-long-range order in the vortex lattice; finally, at larger velocities the ordered array-vortex lattice interaction is suppressed again, in agreement with the behavior found in numerical simulations.

Rectangular arrays of Ni dots with small interdot separation have been fabricated in superconducting Nb films. The geometry of these rectangular arrays defines deep pinning potential channels. Two effects have been observed. ͑i͒ When the vortices move perpendicular to the channels ͑i.e., along the long side of the rectangular array͒ an enhancement of the background pinning is observed, as predicted by theoretical models. This enhancement occurs for all magnetic fields. ͑ii͒ A new anisotropic matching effect, which has not been theoretically predicted, has been measured. The position of the matching fields depends on the direction of the vortex flow. When the vortices move parallel to the potential channels ͑i.e., along the short side of the rectangular array͒ the vortex lattice matches the rectangular array, but when they move along the long side of the rectangular array only a triangular lattice is observed.

Arrays of submicrometric Ni lines have been fabricated in superconducting Nb films by electron beam lithography. In the mixed state, these arrays induce strong anisotropy in the dissipation behavior. The dissipation is reduced several orders of magnitude, in the whole applied magnetic field range, when the vortex motion is perpendicular to the Ni lines ͑applied current parallel to them͒ in comparison with dissipation of vortices moving parallel to the lines. In addition, for the samples studied in this work, a change in the slope of the (B) curves is observed when the vortices move perpendicular to the lines and the vortex lattice parameter matches the width of the Ni lines.

Magneto-optic ͑MO͒ experimental and computational studies are reported on arrays of epitaxial Fe͑001͒ microsquares. Measuring the transverse Kerr signal, in both reflected and diffracted spots, when the array is exposed to a rotating magnetic field allows the quantification of the magnetization inhomogeneties within the microsquares. The MO signal at diffracted spots is extremely sensitive to magnetization inhomogeneities, while working at a large constant field amplitude eliminates uncertainties due to domain-wall movements. The presence of anomalous peaks at the diffracted MO response is unambiguously assigned to the matching of inhomogeneities of the magnetization distribution to the corresponding pattern periodicity. Interaction between microsquares appears as a second-order effect.

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