The upper critical field of NbN films. II

Ashkin, M.; Gavaler, J. R.; Greggi, J.; Decroux, M.

doi:10.1063/1.333185

Cited by 39 publications

(13 citation statements)

References 8 publications

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“…16 NbN also has a cubic structure, but with aϭ4.38 Å, and is a 17 K superconductor with a large upper critical field H c2 Ϸ25 T and a correspondingly short Ginsburg-Landau coherence length of 50 Å. 17 Note the considerable lattice mismatch of ϳ15% between the two materials.…”

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confidence: 99%

Critical fields ofFe4N/NbN ferromagnetic/superconducting multilayers

et al. 1997

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Structural, magnetic, and superconducting properties of ferromagnetic/superconducting multilayers of Fe 4 N/NbN are explored for a variety of thickness combinations. The superconducting properties show that 11 Å ferromagnetic layers are sufficient to decouple the superconducting layers and to yield anisotropic behavior. The upper critical field data are well described by theory for ferromagnetic/superconducting multilayers. This analysis yields an interfacial parameter which characterizes the electron scattering at the ferromagnetic/ superconducting boundary.

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confidence: 99%

Critical fields ofFe4N/NbN ferromagnetic/superconducting multilayers

et al. 1997

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“…H c2// (T) and H c2 (T) can be different 18 . The NbN thin films have been reported to show anisotropic behavior also due to the grain morphology 19 . Thus, we prefer to employ an anisotropic GL (Ginzburg Landau) model to describe the behavior of H c2// (T) in our films, which in the 3D regime ( (T) < d s ) is given by 20,15 : It is interesting to note that the values of T C -T CR for pure NbN and FSB are 0.2 and 1 K respectively.…”

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confidence: 99%

Giant coercivity enhancement and dimensional crossover of superconductivity in Co₂FeSi-NbN nanoscale bilayers

et al. 2013

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Proximity coupling and magnetic switching dynamics are shown to be correlated in bilayers (B) of fully spin polarized ferromagnet (F) Co 2 FeSi and superconductor (S) NbN. The upper critical field derived from resistivity measurements shows a dimensional crossover with a reduced effective thickness of the S layer. At temperatures (T) << superconducting T c , the measured M-H loops show two step switching; one at T-independent value 7 Oe and other at strongly T-dependent value becoming very large 1 kOe at 2 K. These results reveal induced ferromagnetism in S-layer at the S/F interface with vortex pinning influenced dynamics.PACS numbers: 74.45.+c, 74.78.-w, 74.25.Op 2The research field of superconducting (S) and ferromagnetic (F) bilayers (FSB), trilayers and multilayers has gained tremendous importance 1 due to their potential for magnetoeletronics related applications 2 ranging from spin valve to Josephson junctions based devices. The two macroscopic quantum states in S and F layers influence each other via the penetration of superconducting (proximity effect) 2 and ferromagnetic (inverse proximity effect) 3-5 order through their common interface. In presence of strong enough magnetic fields, the vortices in the S-layer can couple with the magnetic domains of the F-layer leading to interesting effects of domain wall pinning of the vortices and vice-a-versa, and domain wall superconductivity [6][7][8][9][10] . Most of such studies have been carried out with ferromagnetic component consisting of 3d transition metals like Fe, Co and Ni, and their alloys. Bilayers of strongly type II superconductors with fully spin polarized ferromagnetic (FSPF) Heusler alloys, which ideally have only one spin state and can potentially show fascinating electronic properties, have not been studied yet. Recently, our group has explored the use of the Co-based Heusler compound (Co 2 MnSi) electrodes for efficient injection of pure spin currents into superconducting NbN 11 . NbN is a type II superconductor of short coherence length ( (0) 5 nm) and long penetration depth ( (0) 200 nm) while Co 2 FeSi (CFS) is a ferromagnet of the Heusler family with high magnetic ordering temperature 1150 K and saturation magnetization 6 µ B per formula unit 12 . In the present work we investigate the nature of proximity coupling and its influence on magnetic switching dynamics in the hitherto unexplored NbN/Co 2 FeSi bilayers grown on (100) MgO.Thin film bilayers of superconducting NbN and CFS were deposited by pulsed laser ablation (PLD). The 35 nm thick NbN film first deposited on MgO at 200 0 C in nitrogen environment by ablating 99.99 % Nb target and then CFS layer of 35 nm thick was grown at the same temperature from a stoichiometric CFS target. To establish the magnetic ordering in CFS film, the FSB sample was annealed at 500 0 C for 1 hour. For comparison, a pure NbN film was also grown during the same PLD run. The other growth parameters for NbN and Co 2 FeSi layers can be found in our previous reports 13,14 . The crystalline quality and interf...

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“…However, junctions in which they were not observed also appeared by repeating the thermal cycle 4.2 to 300 K [12].) From this, we believe that the origin of the Lorentzian spectra exists in the MgO barrier or NbN/MgO interface and is not a defect in the NbN film (for example, a grain caused by a columnar void structure [13] of the NbN film in the neighborhood of the junction), which is the electrode material. We believe that the fact that these kinds of dependence differences in the power spectra of voltage noise appear when the barrier material is changed (AlN → MgO) is related to epitaxial growth, and this is profoundly important in the device fabrication process.…”

Section: Resultsmentioning

confidence: 84%

1/f noise properties of epitaxial NbN/MgO or AlN/NbN tunnel junctions

Ishida

Saito²,

Kawakami³

et al. 2005

Electron. Comm. Jpn. Pt. II

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SUMMARYThe results of comparing the 1/f noise of NbN/MgO or AlN/NbN superconducting tunnel junctions that were epitaxially grown on a MgO (100) single-crystal substrate indicated that the 1/f noise level in a NbN/MgO/NbN junction was practically independent of the critical current density J C (evaluated from the quasiparticle current rise in the gap voltage). However, the 1/f noise level in a NbN/AlN/NbN junction increased suddenly with a decrease in J C . The reason is that since the crystal structure differs for NbN and AlN in the thick film state, as the AlN barrier thickness increases, the effect of the base crystal (NbN) weakens, and NbN/AlN epitaxial growth collapses.

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The upper critical field of NbN films. II

Cited by 39 publications

References 8 publications

Critical fields ofFe4N/NbN ferromagnetic/superconducting multilayers

Critical fields ofFe4N/NbN ferromagnetic/superconducting multilayers

Giant coercivity enhancement and dimensional crossover of superconductivity in Co₂FeSi-NbN nanoscale bilayers

1/f noise properties of epitaxial NbN/MgO or AlN/NbN tunnel junctions

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The upper critical field of NbN films. II

Cited by 39 publications

References 8 publications

Critical fields ofFe4N/NbN ferromagnetic/superconducting multilayers

Critical fields ofFe4N/NbN ferromagnetic/superconducting multilayers

Giant coercivity enhancement and dimensional crossover of superconductivity in Co2FeSi-NbN nanoscale bilayers

1/f noise properties of epitaxial NbN/MgO or AlN/NbN tunnel junctions

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Giant coercivity enhancement and dimensional crossover of superconductivity in Co₂FeSi-NbN nanoscale bilayers