Depairing critical current achieved in superconducting thin films with through-thickness arrays of artificial pinning centers

Abstract

Large area arrays of through-thickness nanoscale pores have been milled into superconducting Nb thin films via a process utilizing anodized aluminum oxide thin film templates. These pores act as artificial flux pinning centers, increasing the superconducting critical current, Jc, of the Nb films. By optimizing the process conditions including anodization time, pore size and milling time, Jc values approaching and in some cases matching the Ginzburg-Landau depairing current of 30 MA/cm 2 at 5 K have been achieved -a Jc enhancement over as-deposited films of more than 50 times. In the field dependence of Jc, a matching field corresponding to the areal pore density has also been clearly observed. The effect of back-filling the pores with magnetic material has then been investigated. While back-filling with Co has been successfully achieved, the effect of the magnetic material on Jc has been found to be largely detrimental compared to voids, although a distinct influence of the magnetic material in producing a hysteretic Jc versus applied field behavior has been observed. This behavior has been tested for compatibility with currently proposed models of magnetic pinning and found to be most closely explained by a model describing the magnetic attraction between the flux vortices and the magnetic inclusions.

Geometry-dependent critical currents in superconducting nanocircuits

“…6 In 2G (second-generation) coated conductors (thickness ∼1 μm and width ∼4 mm) with strong pinning, what normally dominates the critical current is bulk pinning, 43 and except in very rare cases, 44 the critical-current density due to bulk pinning is typically far below the GinzburgLandau depairing critical-current density. 45 However, edge pinning has been shown to play an increasingly dominant role in measurements using narrow strips or bridges (width <10 μm) to assure that the current supply is adequate to do the measurements.…”

Transport critical-current density of superconducting films with hysteretic ferromagnetic dots

“…This additional field can be due to the presence of ferromagnetic materials (FMs) that can be located close to the superconductor [6][7][8] or even inside it. [9][10][11][12][13][14][15][16] The introduction of the FMs inside the SCs can also modify the intrinsic pinning and this is known as magnetic pinning.…”

“…One effect appears in SC-FMs hybrid systems with ferromagnetic parts in the form of ordered structures such as periodic arrays of magnetic dots, 17,18 antidots 19 or even inclusions, 15 for which peaks or plateaus appear in the appliedfield dependence of the critical current and magnetization curve. These effects are commonly known as matching effects and they are produced when an integer number of vortices commensurates at the artificially induced pinning lattice at certain external magnetic fields.…”

“…The choice of this Kim dependence is based on the experimental results of Ref. 15, where the response of superconducting niobium thin films is analyzed when through-thickness nanoscale pores are drilled via an anodized aluminum oxide template and then these pores are backfilled with the magnetic material cobalt. In these experiments, the measured transport J c of the niobium plain film as function of the applied field obeys a Kim-like dependence.…”

“…(1), and assume that the only role of the FM inclusions is to modify the local magnetic field. Choosing typical parameters of the experimental works, 15 our simulated system has dimensions w = 33.77μm, w m = 67 nm, and t = 33.5 nm, and the parameters of the Kim dependence are J c0 = 7MA/cm 2 and μ 0 H 0 = 0.1T. Inside the SC we consider N = 100 FMs with a magnetization in the z direction that obeys the magnetization loop in Fig.…”