Enhanced superconducting vortex pinning with disordered nanomagnetic arrays

We studied the effect of disorder on superconducting vortex pinning produced by arrays of artificial pinning sites. The magnetoresistance of samples with pinning configurations varying from a triangular array to an almost random distribution of pinning sites provides a controlled system for such studies. Interestingly even small degrees of order are sufficient to produce enhanced pinning at well-defined magnetic fields. These effects increase with increasing order and evolve toward the expected matching minima for a triangular array. Surprisingly, the position of the first matching minimum decreases with increasing disorder. Furthermore, additional matching minima appear at higher field values which do not coincide with commonly observed triangular pinning lattice matching minima.