Percolative spin-dependent transport in mesoscopic epitaxial Fe plaquettes of tailored connectivity

Abstract

Spin-dependent charge transport in a two-tier granular system consisting of mesoscopic Fe plaquettes over which silver nanospheres are dispersed is investigated. This system transits from a Coulomb blockade regime with a finite voltage threshold for charge flow to an infinitely connected network showing dynamic resistance as the area coverage by Ag is increased. The zero-bias conductance ͑G V=0 ͒ of the system at low coverage is thermally activated with an energy U ‫ء‬ ͑Ӎ33 meV͒ equivalent to the charging energy of the Ag spheres. The current-voltage curves in this regime show power-law scaling with Ϸ 2.2. A small ͑Ϸ0.8%͒ but distinct low-field ͑Ϸ0.2 T͒ magnetoresistance establishes the spin dependence of the Coulomb energy U ‫ء‬ .

Robust coupling of superconducting order parameter in a mesoscale NbN–Fe–NbN epitaxial structure

“…Our methodology of synthesis utilizes stress-tuned Volmer-Weber (VW) type [10] plaquette growth of Fe on [100] MgO, whose electrical connectivity is tuned by NbN layers of different thickness (d N bN ) deposited on top of the VW template. A KrF excimer laser (λ =248 nm) based pulsed laser ablation technique was used to deposit the nanostructured Fe and epitaxial NbN thin films as described in our earlier works [11,12]. In brief, the growth and the post-growth annealing temperature for Fe plaquettes was ∼700 • C whereas the NbN layer was deposited at 200 • C to inhibit the formation of iron nitride at NbN-Fe interfaces.…”

“…A KrF excimer laser (λ =248 nm) based pulsed laser ablation technique was used to deposit the nanostructured Fe and epitaxial NbN thin films as described in our earlier works [11,12]. In brief, the growth and the post-growth annealing temperature for Fe plaquettes was ∼700 • C whereas the NbN layer The scanning electron micrographs (SEM) of the samples as shown in Fig.…”

“…We also note that the MR for H shows two distinct cusps at ±113 Oe, whose position is higher than the coercive field (H c ∼60 Oe) as measured by SQUID at 5 K. This observation can be understood in the context of number of magnetic entities actually taking part in the magnetization reversal process. Magnetization measurement reflects the total average response of all the magnetic plaquettes, whereas in MR the transport current samples only a fraction of the magnetic plaquettes which fall on its path [11].…”

Magnetotransport in polycrystalline La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ thin films of controlled granularity

“…The distinctive feature in the present case is that the intergrain material is a spin-disordered dirty metal. However, the small mismatch ( 100 Oe) between H P and H C can also be understood by considering the fact that in MR measurement the current circulates only a fraction of the magnetic grains which fall on the percolating path where as the magnetization is a bulk measurement which reflects the average response of the whole sample 38 . The 800 0 C deposited sample showed a better H C vs H P matching may be due to better connectivity between grains therefore a larger fraction of the sample contributes to the MR measurement.…”

Flux-closure pattern in a two-dimensional NbN–Fe superconductor-ferromagnet nanocomposite: Anisotropy of the angular magnetoresistance

“…Further details of film preparation are given elsewhere. 22,23 The Fe layer was deposited first to a nominal thickness of Ϸ40 nm. This was followed by NbN overlayer of thickness 10, 20, and 30 nm.…”