7 research outputs found
Depairing critical current achieved in superconducting thin films with through-thickness arrays of artificial pinning centers
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.Comment: 9 pages, 10 figure
Transport critical-current density of superconducting films with hysteretic ferromagnetic dots
Superconductor-ferromagnet hybrids present a rich and complex phenomenology. Particularly, a hysteretic behavior on the transport critical-current density, as a function of a uniform perpendicular applied field, has been experimentally found in superconducting films with some embedded ferromagnets. Here we analyze the interaction superconductor-ferromagnets by means of an iterative model based on the critical-statemodel with field-dependent internal critical-current density and compare the results with actual transport measurements. By using arguments of field compensation, we show how the change in the magnetization of the ferromagnetic inclusions is responsible for the observed hysteresis on the transport critical current
Superconductor-ferromagnet nanocomposites created by co-deposition of niobium and dysprosium
We have created superconductor-ferromagnet composite films in order to test
the enhancement of critical current density, Jc, due to magnetic pinning. We
co-sputter the type-II superconductor niobium (Nb) and the low-temperature
ferromagnet dysprosium (Dy) onto a heated substrate; the immiscibility of the
two materials leads to a phase-separated composite of magnetic regions within a
superconducting matrix. Over a range of compositions and substrate
temperatures, we achieve phase separation on scales from 5 nm to 1 micron. The
composite films exhibit simultaneous superconductivity and ferromagnetism.
Transport measurements show that while the self-field Jc is reduced in the
composites, the in-field Jc is greatly enhanced up to the 3 T saturation field
of Dy. In one instance, the phase separation orders into stripes, leading to
in-plane anisotropy in Jc.Comment: 7 pages, 7 figures. Matches the version published in SUST: Added one
reference and some discussion in Section
Transport critical-current density of superconducting films with hysteretic ferromagnetic dots
Superconductor-ferromagnet hybrids present a rich and complex phenomenology. Particularly, a hysteretic behavior on the transport critical-current density, as a function of a uniform perpendicular applied field, has been experimentally found in superconducting films with some embedded ferromagnets. Here we analyze the interaction superconductor-ferromagnets by means of an iterative model based on the critical-statemodel with field-dependent internal critical-current density and compare the results with actual transport measurements. By using arguments of field compensation, we show how the change in the magnetization of the ferromagnetic inclusions is responsible for the observed hysteresis on the transport critical current