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Planar Superconductor-Ferromagnet-Superconductor Josephson Junctions as Scanning-Probe Sensors
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics. Moscow Institute of Physics and Technology, State University, Russia.ORCID iD: 0000-0002-3131-8658
Number of Authors: 32019 (English)In: Physical Review Applied, E-ISSN 2331-7019, Vol. 11, no 1, article id 014062Article in journal (Refereed) Published
Abstract [en]

We propose a magnetic scanning-probe sensor based on a single-planar Josephson junction with a magnetic barrier. The planar geometry together with the high magnetic permeability of the barrier facilitates a double flux-focusing effect, which helps to guide magnetic flux into the junction and thus enhances field sensitivity of the sensor. We fabricate and analyze experimentally sensor prototypes with a superparamagnetic Cu−Ni and a ferromagnetic Ni barrier. We demonstrate that the planar geometry allows easy miniaturization to nanometer scale and facilitates an effective utilization of the self-field phenomenon for amplification of sensitivity and a simple implementation of a control line for feedback operation over a broad dynamic range. We argue that the proposed sensor can outperform equally sized superconducting quantum-interference devices (SQUIDs) both in terms of magnetic-field sensitivity and spatial resolution, which makes it advantageous for scanning-probe microscopy.

Place, publisher, year, edition, pages
2019. Vol. 11, no 1, article id 014062
Keywords [en]
Superconductivity, Josephson effect, Scanning probe microscopy
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:su:diva-166785DOI: 10.1103/PhysRevApplied.11.014062ISI: 000457141300003Scopus ID: 2-s2.0-85060986817OAI: oai:DiVA.org:su-166785DiVA, id: diva2:1295706
Available from: 2019-03-12 Created: 2019-03-12 Last updated: 2022-11-03Bibliographically approved
In thesis
1. Hybrid Superconductor/Ferromagnet junctions with a strongly ferromagnetic barrier
Open this publication in new window or tab >>Hybrid Superconductor/Ferromagnet junctions with a strongly ferromagnetic barrier
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2019
Keywords
Superconductivity, Josephson junctions, planar Josephson junctions, micro/nanoscale fabrication, micromagnetic state, in-situ characterization technique
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-176283 (URN)
Presentation
2019-12-19, FP22, hus 1, AlbaNova universitetcentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2019-12-09 Created: 2019-11-27 Last updated: 2022-02-26Bibliographically approved

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Publisher's full textScopusarXiv:1806.05582

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Golod, TarasKapran, Olena M.Krasnov, Vladimir M.

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