Vortex pinning vs superconducting wire network: origin of periodic oscillations induced by applied magnetic fields in superconducting films with arrays of nanomagnets

Abstract

Abstract. Hybrid magnetic arrays embedded in superconducting films are ideal systems to study the competition between different physical (such as the coherence length) and structural length scales such as available in artificially produced structures. This interplay leads to oscillation in many magnetically dependent superconducting properties such as the critical currents, resistivity and magnetization. These effects are generally analyzed using two distinct models based on vortex pinning or wire network. In this work, we show that for magnetic dot arrays, as opposed to antidot (i.e holes) arrays, vortex pinning is the main mechanism for field induced oscillations in resistance R(H), critical current I c (H), magnetization M(H) and ac-susceptibility  ac (H) in a broad temperature range. Due to the coherence length divergence at T c , a crossover to wire network behaviour is experimentally found. While pinning occurs in a wide temperature range up to T c , wire network behaviour is only present in a very narrow temperature window close to T c . In this temperature interval, contributions from both mechanisms are operational but can be experimentally distinguished.

Thickness-modulated tungsten–carbon superconducting nanostructures grown by focused ion beam induced deposition for vortex pinning up to high magnetic fields

“…7. The measurement of the critical current as a function of the magnetic field has been carried out for the sample with pitch 100 nm at 1.9 K in order to verify that a minimum in the resistance corresponds to a maximum in the critical current, as previously observed in other superconductors governed by pinning effects [38–39 41,51]. In these measurements, the voltage is limited to a threshold value that corresponds to the crossover from the superconducting to the normal state of the sample.…”

Little–Parks effect governed by magnetic nanostructures with out-of-plane magnetization

“…The magnetoresistance curves are shifted right or left depending on the direction of the applied fields and the out-of-plane remanent magnetization in the dots. This means that superconducting vortices and antivortices are present in this situation and they coexist with the L-P effect in the wire network regime (16)(17)(18)(19). To figure out the exact origin of this magnetic influenced L-P effect we have to consider not only the vortex dynamics, but also the magnetism of the SCP dots and the direction of the applied fields, as it was discussed in the previous section.…”

“…To figure out the exact origin of this magnetic influenced L-P effect we have to consider not only the vortex dynamics, but also the magnetism of the SCP dots and the direction of the applied fields, as it was discussed in the previous section. Gomez et al (19) showed that effects related to vortex dynamics are present in the whole range of temperatures and they coexist with the L-P effect close to Tc0. The clear difference between the SN and SCP samples, although having the same geometry, indicates that the clue to understand the L-P effect in the SCP sample is the role played by the magnetic stray fields emerging from the outof-plane dot magnetization.…”

“…The interplay between superconducting vortices and L-P effect has to be considered too. So far, several studies have addressed the role of the vortex movement in systems which also present the L-P effect; for instance, Berdiyorov et al (16) show that the vortex effect should be considered in parallel with the Little-Parks effect; Sochnikov et al (17) study the interaction between thermally excited moving vortices and the oscillating persistent currents induced in the superconducting loops; Welp et al (18) and Gomez et al (19) study the interplay between vortex pinning and L-P effect. One interesting scenario is L-P effect in hybrid superconductors shaped by periodically arranged magnetic nanostructures.…”

“…Since superconductivity is depressed in the vicinity of the magnetic islands , the network consists of superconducting channels (wires) in between those areas where the superconductivity is strongly depleted by the array of magnetic dots. Quite a few works have dealt with this type of samples (array of magnetic dots on top or embedded in superconducting films), see review (20) and references therein; but to our knowledge, only few of them have focused on the experimental study of L-P effect in these nanostructures in the wire network regime (19,(21)(22)(23). The aim of this work is to explore whether or not the magnetism of the dots plays any role in the L-P effect.…”