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Hybrid Superconduct...
Hybrid Superconductor/Ferromagnet junctions with a strongly ferromagnetic barrier
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- Kapran, Olena, 1993- (författare)
- Stockholms universitet,Fysikum
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- Krasnov, Vladimir, Professor (preses)
- Stockholms universitet,Fysikum
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- Bauch, Thilo, Docent (opponent)
- MINA, Chalmers Tekniska Högskola
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(creator_code:org_t)
- Stockholm : Department of Physics, Stockholm University, 2019
- Engelska.
- Relaterad länk:
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https://urn.kb.se/re...
Abstract
Ämnesord
Stäng
- The spin-triplet superconducting state, predicted in superconductor /ferromagnet heterostructures remains one of the most exotic states of nature. It is expected that the triplet state can be switched on/off by changing the relative orientation of magnetization in multilayer Josephson spin-valve structures. This is interesting not only from a fundamental point but could also lead to the creation of novel transistor-like devices with controlled supercurrent. However, there are many experimental challenges. The key issue is in achieving detailed knowledge and control of the micromagnetic state. This requires methods for in-situ characterization of actual nano-devices.In this thesis we study Superconductor/Ferromagnet/Superconductor (SFS) Josephson junctions with Nb superconducting electrodes and Ni interlayers with thicknesses 2-20 nm. Nano-scale SFS junctions are made by a 3D nanosculpturing technique by Focused Ion Beam. Small sizes are needed for achieving mono-domain remagnetization of Ni interlayer in the junctions. Ni is a strong ferromagnet with the exchange energy Eex ~ 631 K much larger than the superconducting critical temperature of Nb, Tc ≈9 K. Therefore, it might be expected that spin-singlet Cooper pairs should be rapidly destroyed in Ni. However, we observe a significant supercurrent through Ni with thicknesses up to 20 nm. We attribute this counterintuitive result to the cleanliness of Ni films with a mean-free-path ~100 nm larger than the film thickness. For determination of the micromagnetic state of F-layers in our nano-scale junctions we develop a new in-situ characterization technique based on a combination of the Absolute Josephson Fluxometry and the First-Order-Reversal-Curves analysis. It is demonstrated that this is a very powerful technique facilitating detailed in-situ measurements of magnetization curves of F-interlayers even in very small junctions. Finally, we fabricate and study nano-scale Nb/Ni/Nb junctions with planar geometry and argue that such junctions can be employed as sensitive scanning-probe sensors. Thus, we demonstrate that Ni, despite being a strong ferromagnet, is a promising material for application in superconducting spintronics.
Ämnesord
- NATURVETENSKAP -- Fysik -- Den kondenserade materiens fysik (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Condensed Matter Physics (hsv//eng)
Nyckelord
- Superconductivity
- Josephson junctions
- planar Josephson junctions
- micro/nanoscale fabrication
- micromagnetic state
- in-situ characterization technique
- fysik
- Physics
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