Pinning centers produced by magnetic microstructures

Abstract

We investigate the flux pinning and dynamic properties of superconducting vortices in an Al film with an array of magnetic bars deposited on top. The dimensions of each bar are chosen in such a way that they host a single magnetic domain. These micromagnets are distributed periodically in a rectangular array with 0.5 μm separation parallel to the longest side of the bars and displaced laterally by a distance w. We show that, for w > , where is the effective field penetration depth, the pinning strength is almost independent of w whereas the critical temperature at zero field, T c (0), decreases as ∼w −1 . For w < the opposite behavior is observed, i.e. T c (0) seems to saturate to a nearly w-independent value and the transition from large to small w is accompanied by a large suppression of the critical current j c together with a clear change in the shape of the current-voltage characteristics. In particular, the substantial weakening of the pinning potential for w < gives rise to an unexpected flux flow response. The field evolution of this regime allows us to determine whether the magnetic bars induce vortex-antivortex pairs in the system. The present findings suggest that practical application of magnetic pinning centers are restricted to low field values.

Flow and Tilt-Induced Orientation of the Moving Vortex Lattice in Amorphous NbGe Superconducting Thin Films

“…A further test of the SV model can be made on confined vortex systems such as narrow constrictions 41,[46][47][48][49][50] or possibly small disks. 51,52) The shear rigidity of moving lattices appears in the transport properties such as the flux-flow resistance, and the anisotropy in VL parameters can be tuned by the matching condition between the vortex density and the size of the constriction.…”

Evidence for low-field crossover in the vortex critical velocity of type-II superconducting thin films

“…[1][2][3] On the contrary, an attractive interest has been recently devoted to different superconducting materials in which inhomogeneous states are induced by the type of pinning, intrinsic or extrinsic, causing nonlinearities of the flux flow motion resulting in a preferential as well as a directional motion of vortices. [4][5][6][7][8] At high driving currents the current-voltage (I-V) characteristics show an abrupt switching from the linear flux flow state into the normal state at a threshold voltage V * . This voltage jump can be accounted for different intrinsic or extrinsic mechanisms such as for example Joule heating.…”

Magnetically controlled superconducting weak links

“…Note that the existence of a flux flow regime even at zero applied field is a clear indication of the presence of internally induced vortex channels in the p state. 13,14 There are two characteristic behaviors resulting from the phase coherence across a weak link, the Fraunhofer-like pattern of the critical current as a function of field, and the presence of Shapiro steps in the V͑I͒ characteristics. The fact that the dynamics of our system is dominated by the strongly inhomogeneous stray field generated by the magnetic template suggests that the Fraunhofer-like pattern in I c ͑H͒ can be severely modified.…”