The influence of a submicrometre antidot array on the vortex topology and the pinning mechanism in layered superconductors

Measurements of the critical current density dependence on the direction of the external magnetic field vector H have been performed on Nb/CuMn multilayers with and without a regular square lattice of submicrometre antidots. (i) At small angles between H and the surface of the sample, the presence of the antidot array strongly influences the topology of the flux lines. In the multilayers without the antidot array the vortex topology is mainly due to the anisotropy of the system with the formation of kinked vortices in the samples with higher values of the anisotropy parameter. In antidotted samples, the presence of kinked vortices is not related to the anisotropy of the system but to the geometry of the antidot array. (ii) At large angles between H and the surface of the sample, the dimensions of the antidots determine the pinning mechanism, with the prevalence of edge pinning when the antidot diameter is larger than the magnetic penetration depth lambda and the presence of electromagnetic pinning when the diameter is comparable to lambda. A phenomenological expression for the angular dependence of the pinning force at intermediate and large angles is proposed, satisfactorily describing the experimental data.