Sophie Raedts

Guided vortex motion in superconductors with a square antidot array

We have measured the in-plane anisotropy of the vortex mobility in a thin Pb film with a square array of antidots. Τhe Lorentz force, acting on the vortices, was rotated by adding two perpendicular currents and keeping the amplitude of the net current constant. One set of voltage probes was used to detect the vortex motion. We show that the pinning landscape provided by the square antidot lattice influences the vortex motion in two different ways. First, the modulus of the vortex velocity becomes angular dependent with a lower mobility along the diagonals of the pinning array. Second, the vortex displacement is preferentially parallel to the principal axes of the underlying pinning lattice, giving rise to a misalignment between the vortex velocity and the applied Lorentz force. We show that this anisotropic vortex motion is temperature dependent and progressively fades out when approaching the normal state.

Enhanced vortex pinning by a composite antidot lattice in a superconducting Pb film

The use of artificial defects is known to enhance the superconducting critical parameters of thin films. In the case of conventional superconductors, regular arrays of submicron holes (antidots) substantially increase the critical temperature

Flux-pinning properties of superconducting films with arrays of blind holes

{T}_{c}(H)

Dendritic flux penetration in Pb films with a periodic array of antidots

and critical current

Field-dependent vortex pinning strength in a periodic array of antidots

{I}_{c}(H)

Magnetic domains and flux pinning properties of a nanostructured ferromagnet/superconductor bilayer

for all fields. Using electrical transport measurements, we study the effect of placing an additional small antidot in the unit cell of the array. This composite antidot lattice consists of two interpenetrating antidot square arrays with a different antidot size and the same lattice period. The smaller antidots are located at the centers of the cells of the large antidots array. We show that the composite antidot lattice can trap a higher number of flux quanta per unit cell inside the antidots compared to a reference antidot film without the additional small antidots. As a consequence, the field range in which an enhanced critical current is observed is considerably expanded. Finally, the possible stable vortex lattice patterns at several matching fields are determined by molecular-dynamics simulations.

Pinning of domain walls and flux lines in a nanostructured ferromagnet/superconductor bilayer

We performed ac susceptibility measurements to explore the vortex dynamics and the flux-pinning properties of superconducting Pb films with an array of microholes (antidots) and not fully perforated holes (blind holes). A lower ac shielding together with a smaller extension of the linear regime for the lattice of blind holes indicates that these centers provide a weaker pinning potential than antidots. Moreover, we found that the maximum number of flux quanta trapped by a pinning site, i.e., the saturation number

Dynamic regimes in films with a periodic array of antidots

{n}_{s}

Nanostructured Superconductor/Ferromagnet Bilayers

, is lower for the blind hole array.

Hybrid Superconductor/Ferromagnet Nanostructures

We explore the flux-jump regime in type-II Pb thin films with a periodic array of antidots by means of magneto-optical measurements. A direct visualization of the magnetic flux distribution allows us to identify a rich morphology of flux penetration patterns. We determine the phase boundary