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arxiv: 1907.08406 · v1 · pith:RLVBV3AEnew · submitted 2019-07-19 · ❄️ cond-mat.supr-con

Magnetic-field-orientation-dependent triplet supercurrents in Josephson junctions with symmetric and asymmetric exchange-spring interfaces

Ekta Bhatia , J. M. Devine-Stoneman , S. Komori , A. Srivastava , N. A. Stelmashenko , Z. H. Barber , K. Senapati , J. W. A. Robinson This is my paper

Pith reviewed 2026-05-24 19:08 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con
keywords Josephson junctiontriplet supercurrentexchange-spring interfaceCo/Pyferromagnetic layermagnetic inhomogeneitysinglet-triplet conversionsupercurrent
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The pith

Magnetic field orientation tunes triplet supercurrents through thick Py in Josephson junctions with Co/Py exchange-spring interfaces.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines Josephson junctions that pair s-wave superconductors with multiple ferromagnetic layers using exchange-spring Co/Py interfaces. An external magnetic field induces a non-collinear magnetic structure in Py at the interface, which supplies the inhomogeneity needed to convert singlet Cooper pairs into triplet pairs. Supercurrents are then observed to travel through Py layers thicker than 10 nm, well beyond the singlet coherence length. A reader would care because this points to a route for magnetic control of supercurrents in hybrid devices where the current can be adjusted by field direction and strength rather than by changing layer thicknesses alone.

Core claim

In Josephson junctions with s-wave superconductors and ferromagnetic layers that incorporate exchange-spring and double exchange-spring Co/Py interfaces, supercurrents are detected through Py thicknesses exceeding 10 nm. This distance greatly exceeds the singlet pair coherence length and indicates the presence of magnetically tunable triplet supercurrents that arise from the non-collinear magnetic structure formed at the Co/Py interface, whose configuration depends on the direction and magnitude of the applied field.

What carries the argument

The exchange-spring Co/Py interface, in which strong exchange coupling relative to Py anisotropy produces a field-dependent non-collinear magnetic structure that supplies the inhomogeneity for singlet-to-triplet pair conversion.

If this is right

  • Supercurrents persist through ferromagnetic layers much thicker than the singlet coherence length when triplet pairs are generated at the interface.
  • The supercurrent amplitude and presence can be adjusted by rotating the direction of an external magnetic field.
  • The same interface mechanism operates in both symmetric and asymmetric exchange-spring configurations.
  • Triplet supercurrents become magnetically tunable without requiring changes to layer thicknesses.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Field-angle control could be used to switch the Josephson current on and off in a single device by small rotations of the applied field.
  • Exchange-spring interfaces of this type might be combined with other ferromagnetic materials to extend the range of triplet supercurrents in additional hybrid structures.
  • The observed thickness dependence offers a direct experimental test for the efficiency of the singlet-to-triplet conversion process at the interface.

Load-bearing premise

The non-collinear magnetic structure that forms in Py at the Co/Py interface, depending on external field direction and magnitude, creates the magnetic inhomogeneity required for singlet-to-triplet pair conversion.

What would settle it

A measurement showing that supercurrent through Py thicker than 10 nm decays with thickness at the short length scale expected for singlet pairs or shows no systematic dependence on the angle of the applied field.

Figures

Figures reproduced from arXiv: 1907.08406 by A. Srivastava, Ekta Bhatia, J. M. Devine-Stoneman, J. W. A. Robinson, K. Senapati, N. A. Stelmashenko, S. Komori, Z. H. Barber.

Figure 1
Figure 1. Figure 1: Magnetic characterization of a Co/Py XS. (a) Major and minor M(H) loops of an unpatterned Nb(220 nm)/Co(2 nm)/Py(11 nm)/Nb(220 nm) multilayer at 10 K with H in-plane. For a range of magnetic fields the minor loops are reversible, consistent with exchange-spring behavior. (b) The field derivative curve of an unpatterned Nb/Co(2 nm)/Py(11 nm)/Nb multilayer at 10 K. (c) Schematic illustration of a nanopillar … view at source ↗
Figure 2
Figure 2. Figure 2: Characterization of a Nb/Py(7 nm)/Co(2 nm)/Py(7 nm)/Nb double XS Josephson junction. (a) Fraunhofer modulation of Ic(H) of double XS junction at 1.6 K. (b) Critical current vs direction of applied magnetic field showing manipulation of triplet supercurrents for double XS junction with dimensions of ∼(300×300) nm2 at 1.6 K with in-plane field 20 mT, at different angles (θ) of the applied field with respect … view at source ↗
Figure 3
Figure 3. Figure 3: Characterization of Nb/Co(2 nm)/Py(11 nm)/Nb XS Josephson junction (a) Fraun￾hofer modulation of Ic(H) of a XS junction at 4.2 K. Inset shows the low field regime of Ic(H), with hysteresis. (b) R vs direction of applied magnetic field showing manipulation of triplet su￾percurrents in the same sample with dimensions of ∼(300×300) nm2 at 1.6 K with in-plane fields of 400 mT, 20 mT and 0 mT at different angle… view at source ↗
Figure 4
Figure 4. Figure 4: Comparisons showing the long range nature of supercurrent in a S/XS/S magnetic Josephson junction (a) I(V) characteristics of a Nb(220 nm)/Co(2 nm)/Py(7 nm)/Nb(220 nm) junction and a Nb(220 nm)/Py(6 nm)/Nb(220 nm) junction at 4.2 K and zero magnetic field. (b) Comparison of I(V) of a Nb/Co(2 nm)/Py(11 nm)/Nb junction with a Nb(220 nm)/Co(2 nm)/Cu(4 nm)/Py(11 nm)/Nb(220 nm) junction at 4.2 K and zero field.… view at source ↗
Figure 5
Figure 5. Figure 5: Supercurrent decays in Py. IcRN vs. total thickness of Py; the grey curve presents the IcRN for Py-only junctions (taken from Ref. 32). As dPy increases above 5 nm, IcRN is practically zero but introducing Co results in an enhancement of IcRN which decays slowly. Inset shows IcRN for a double spring junction vs total thickness of Py. 20 [PITH_FULL_IMAGE:figures/full_fig_p020_5.png] view at source ↗
read the original abstract

Josephson junctions with s-wave superconductors (S) and multiple ferromagnetic (F) layers carry spin-triplet supercurrents in the presence of magnetically inhomogeneous spin-mixer interfaces. Here, we report magnetic Josephson junctions with exchange-spring and double exchange-spring ("spin-mixer") Co/Py interfaces. At the Co/Py interface, exchange coupling is strong with respect to the magnetic anisotropy of Py and so, depending on the direction and magnitude of an external magnetic field, a non-collinear magnetic structure forms in Py creating the necessary magnetic inhomogeneity for singlet-to-triplet pair conversion. We detect supercurrents through Py with a thickness exceeding 10 nm, which is much larger than the singlet pair coherence length, suggesting the propagation of magnetically tuneable triplet supercurrents.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The manuscript reports Josephson junctions with s-wave superconductors and exchange-spring Co/Py interfaces. It claims that strong exchange coupling relative to Py anisotropy produces field-orientation-dependent non-collinear magnetization in Py, enabling singlet-to-triplet pair conversion and thereby allowing supercurrents to propagate through Py layers thicker than 10 nm (exceeding the singlet coherence length).

Significance. If the central experimental claim is substantiated with direct evidence for the magnetization profile, the result would demonstrate a field-tunable mechanism for generating long-range triplet supercurrents at a relatively simple spin-mixer interface, with potential implications for superconducting spintronics devices that rely on magnetic control of supercurrent.

major comments (1)
  1. [Abstract] Abstract: The attribution of the observed supercurrent through >10 nm Py to triplet conversion rests on the formation of a non-collinear magnetic structure in Py at the Co/Py interface. However, the text provides no magnetometry, micromagnetic modeling, or field-angle-dependent resistance data on the actual multilayer stacks to confirm that the required magnetic inhomogeneity is present under the measurement conditions.
minor comments (1)
  1. [Abstract] The abstract states key observations but omits quantitative details such as exact layer thicknesses, critical current values, error bars, or temperature dependence that would allow independent assessment of the coherence length comparison.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for highlighting this important point regarding evidence for the magnetic structure. We respond to the major comment below.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The attribution of the observed supercurrent through >10 nm Py to triplet conversion rests on the formation of a non-collinear magnetic structure in Py at the Co/Py interface. However, the text provides no magnetometry, micromagnetic modeling, or field-angle-dependent resistance data on the actual multilayer stacks to confirm that the required magnetic inhomogeneity is present under the measurement conditions.

    Authors: We agree that direct magnetometry or micromagnetic modeling on the precise multilayer stacks would provide stronger substantiation. The manuscript infers the non-collinear Py structure from the known strong exchange coupling at Co/Py relative to Py's weak anisotropy, which produces field-orientation-dependent canting (as established in prior exchange-spring literature). The observed supercurrent's dependence on field orientation is presented as indirect evidence consistent with this inhomogeneity. We will add micromagnetic simulations of the Co/Py bilayer under the experimental field angles and magnitudes to the revised manuscript (including supplementary material) to explicitly model the expected magnetization profile. We do not possess magnetometry data on the exact junction stacks, as device fabrication precludes standard measurements on completed junctions, but the simulations will address the core concern. revision: partial

Circularity Check

0 steps flagged

No circularity: experimental report with direct measurements

full rationale

The paper is an experimental measurement report on Josephson junctions. The central claim (supercurrent through >10 nm Py exceeding singlet coherence length) is presented as a direct observation, with the non-collinear magnetization offered as a physical interpretation rather than a derived result. No equations, fitted parameters renamed as predictions, self-citation load-bearing premises, or ansatzes smuggled via citation appear in the abstract or described chain. The derivation chain is absent; the work is self-contained against external benchmarks via measurement.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on experimental measurements interpreted via established superconductivity theory; no new free parameters, ad-hoc axioms, or invented entities are introduced in the abstract.

axioms (1)
  • standard math Standard assumptions of s-wave superconductivity and singlet-triplet conversion in the presence of magnetic inhomogeneity
    The interpretation of observed supercurrents as triplet pairs relies on prior theoretical framework for pair conversion at spin-mixer interfaces.

pith-pipeline@v0.9.0 · 5709 in / 1298 out tokens · 30899 ms · 2026-05-24T19:08:39.632745+00:00 · methodology

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Reference graph

Works this paper leans on

38 extracted references · 38 canonical work pages

  1. [1]

    Buzdin, A. I. Proximity effects in superconductor-ferromagnet heterostructures. Rev. Mod. Phys. 77, 935 (2005)

    work page 2005

  2. [2]

    S., V olkov, A

    Bergeret, F. S., V olkov, A. F. & Efetov, K. B. Long-range proximity effects in superconductor- ferromagnet structures. Phys. Rev. Lett. 86, 4096 (2001)

    work page 2001

  3. [3]

    & Robinson, J

    Linder, J. & Robinson, J. W. A. Superconducting spintronics. Nat. Phys. 11, 307315 (2015)

    work page 2015

  4. [4]

    Eschrig, M. Rep. Prog. Phys. 78, 104501 (2015)

    work page 2015

  5. [5]

    Blamire, M. G. & Robinson, J. W. A. Spin-polarized supercurrents for spintronics: a review of current progress. J. Phys. Condens. Matter 26, 453201 (2014)

    work page 2014

  6. [6]

    S., Goennenwein, S

    Keizer, R. S., Goennenwein, S. T. B., Klapwijk, T. M., Miao, G. X., Xiao, G. & Gupta, A. A spin triplet supercurrent through the half-metallic ferromagnet CrO 2. Nature 439, 825827 (2006)

    work page 2006

  7. [7]

    S., Khasawneh, M

    Khaire, T. S., Khasawneh, M. A., Pratt, W. P. & Birge, N. O. Observation of spin-triplet super- conductivity in Co-based Josephson junctions. Phys. Rev. Lett. 104, 137002 (2010)

    work page 2010

  8. [8]

    Robinson, J. W. A., Witt, J. D. S. & Blamire, M. G. Controlled injection of spin-triplet super- currents into a strong ferromagnet. Science 329, 5961 (2010). 10

    work page 2010

  9. [9]

    Robinson, J. W. A., Hal ´asz, G. B., Buzdin, A. I. & Blamire, M. G. Enhanced supercurrents in Josephson junctions containing nonparallel ferromagnetic domains. Phys. Rev. Lett. 104, 207001 (2010)

    work page 2010

  10. [10]

    Klose, C. et al. Optimization of Spin-Triplet Supercurrent in Ferromagnetic Josephson Junc- tions. Phys. Rev. Lett. 108, 127002 (2012)

    work page 2012

  11. [11]

    Kalcheim, Y ., Millo, O., Egilmez, M., Robinson, J. W. A. & Blamire, M. G. Evi- dence for anisotropic triplet superconductor order parameter in half-metallic ferromagnetic La0.7Ca0.3Mn3O proximity coupled to superconducting Pr 1.85Ce0.15CuO4. Phys. Rev. B 85, 104504 (2012)

    work page 2012

  12. [12]

    & Krasnov, V

    Iovan, A., Golod, T. & Krasnov, V . M. Controllable generation of a spin-triplet supercurrent in a Josephson spin valve. Phys. Rev. B 90, 134514 (2014)

    work page 2014

  13. [13]

    D., Diesch, S., Gu, Y ., Linder, J., Divitini, G., Ducati, C., Scheer, E., Blamire, M

    Bernardo, A. D., Diesch, S., Gu, Y ., Linder, J., Divitini, G., Ducati, C., Scheer, E., Blamire, M. G. & Robinson, J. W. A. Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces. Nat. Commun. 6, 8053 (2015)

    work page 2015

  14. [14]

    J., Kurebayashi, H., Cohen, L

    Jeon, K.-R., Ciccarelli, C., Ferguson, A. J., Kurebayashi, H., Cohen, L. F., Montiel, X., Es- chrig, M., Robinson, J. W. A. & Blamire, M. G. Enhanced spin pumping into superconductors provides evidence for superconducting pure spin currents. Nat. Mater .17, 499503 (2018)

    work page 2018

  15. [15]

    F., Montiel, X., Eschrig, M., Komori, S., Robinson, J

    Jeon, K.-R., Ciccarelli, C., Kurebayashi, H., Cohen, L. F., Montiel, X., Eschrig, M., Komori, S., Robinson, J. W. A. & Blamire M. G. Exchange-field enhancement of superconducting spin pumping. Phys. Rev. B 99, 024507 (2019) 11

    work page 2019

  16. [16]

    & Buzdin, A

    Houzet, M. & Buzdin, A. I. Long range triplet Josephson effect through a ferromagnetic tri- layer. Phys. Rev. B 76, 060504(R) (2007)

    work page 2007

  17. [17]

    & Meyer, J

    Richard, C., Houzet, M. & Meyer, J. S. Superharmonic long-range triplet current in a diffusive Josephson junction. Phys. Rev. Lett. 110, 217004 (2013)

    work page 2013

  18. [18]

    & Ren, Y ., Long-range superharmonic Josephson current and spin-triplet pairing correlations in a junction with ferromagnetic bilayers.Sci

    Meng, H., Wu, J., Wu, X., Ren, M. & Ren, Y ., Long-range superharmonic Josephson current and spin-triplet pairing correlations in a junction with ferromagnetic bilayers.Sci. Rep. 6, 21308 (2016)

    work page 2016

  19. [19]

    Banerjee, N., Robinson, J. W. A. & Blamire, M. G., Reversible control of spin-polarized supercurrents in ferromagnetic Josephson junctions. Nat. Commun. 5, 4771 (2014)

    work page 2014

  20. [20]

    V ., Garifyanov, N

    Leksin, P. V ., Garifyanov, N. N., Garifullin, I. A., Fominov, Y . V ., Schumann, J., Krup- skaya, Y ., Kataev, V ., Schmidt, O. G., & B ¨uchner, B. Evidence for triplet superconductivity in a superconductor-ferromagnet spin valve. Phys. Rev. Lett. 109, 057005 (2012)

    work page 2012

  21. [21]

    L., Bernardo, A

    Wang, X. L., Bernardo, A. Di, Banerjee, N., Wells, A., Bergeret, F. S., Blamire, M. G. & Robinson, J. W. A. Giant triplet proximity effect in superconducting pseudo spin valves with engineered anisotropy. Phys. Rev. B 89, 140508 (2014)

    work page 2014

  22. [22]

    G., Cunningham, T

    Flokstra, M. G., Cunningham, T. C., Kim, J., Satchell, N., Burnell, G., Curran, P. J., Bending, S. J., Kinane, C. J., Cooper, J. F. K., Langridge, S., Isidori, A., Pugach, N., Eschrig, M. & Lee, S. L. Controlled suppression of superconductivity by the generation of polarized Cooper pairs in spin-valve structures. Phys. Rev. B 91, 060501 (2015). 12

    work page 2015

  23. [23]

    & Aarts, J

    Singh, A., V oltan, S., Lahabi, K. & Aarts, J. Colossal proximity effect in a superconducting triplet spin valve based on the half-metallic ferromagnet CrO2. Phys. Rev. X 5, 021019 (2015)

    work page 2015

  24. [24]

    & Robinson J.W.A

    Srivastava, A., Olde Olthof, L.A.B., Di Bernardo, A., Komori, S., Amado, M., Palomares- Garcia, C., Alidoust, M., Halterman, K., Blamire, M.G. & Robinson J.W.A. Magnetization Control and Transfer of Spin-Polarized Cooper Pairs into a Half-Metal Manganite. Phys. Rev. Applied 8, 044008 (2017)

    work page 2017

  25. [25]

    Feng, Z., Robinson, J. W. A. & Blamire, M. G. Out of plane superconducting Nb/Cu/Ni/Cu/Co triplet spin-valves. Appl. Phys. Lett. 111, 042602 (2017)

    work page 2017

  26. [26]

    M., Pratt, W

    Martinez, W. M., Pratt, W. P. Jr. & Birge, N. O. Amplitude control of the spin-triplet supercur- rent in S/F/S Josephson junctions. Phys. Rev. Lett. 116, 077001 (2016)

    work page 2016

  27. [27]

    & Braun, H

    Bill, A. & Braun, H. B. Magnetic properties of exchange springs. J. Magn. Magn. Mater .272, 1266 (2004)

    work page 2004

  28. [28]

    E., Richie-Halford, A

    Baker, T. E., Richie-Halford, A. & Bill, A. Long range triplet Josephson current and 0- π transitions in tunable domain walls. New J. Phys. 16, 093048 (2014)

    work page 2014

  29. [29]

    Y ., Kusnadi, J

    Gu, J. Y ., Kusnadi, J. & You, C.-Y . Proximity effect in a superconductor/exchange-spring- magnet hybrid system. Phys. Rev. B 81, 214435 (2010)

    work page 2010

  30. [30]

    S., Pearson, J

    Zhu, L.Y ., Liu, Y ., Bergeret, F. S., Pearson, J. E., Velthuis, S. G. E. te, Bader, S. D. & Jiang, J. S. Unanticipated proximity behavior in ferromagnet-superconductor heterostructures with controlled magnetic noncollinearity. Phys. Rev. Lett. 110, 177001 (2013). 13

    work page 2013

  31. [31]

    Robinson, J. W. A., Piano, S., Burnell, G., Bell, C., Blamire, M. G. Critical Current Oscilla- tions in Strong Ferromagneticπ Junctions. Phys. Rev. Lett. 97, 177003 (2006)

    work page 2006

  32. [32]

    Robinson, J. W. A., Piano, S., Burnell, G., Bell, C., Blamire, M. G. Zero to π transition in superconductor-ferromagnet-superconductor junctions. Phys. Rev. B 76, 094522 (2007)

    work page 2007

  33. [33]

    H., Kappers, M

    Bell, C., Burnell, G., Kang, D.-J., Hadfield, R. H., Kappers, M. J. & Blamire, M. G. Fabrica- tion of nanoscale heterostructure devices with a focused ion beam microscope.Nanotechnology 14, 630 (2003)

    work page 2003

  34. [34]

    F., Heyderman, L

    Rodr ´ıguez, A. F., Heyderman, L. J., Nolting, F., Hoffmann, A., Pearson, J. E., Doeswijk, L. M., van den Boogaart, M. A. F. & Brugger, J. Permalloy thin films exchange coupled to arrays of cobalt islands. Appl. Phys. Lett. 89, 142508 (2006)

    work page 2006

  35. [35]

    F., Arzuza, L

    B ´eron, F., Kaidatzis, A., Velo, M. F., Arzuza, L. C. C., Palmero, E. M., del Real, R. P., Niar- chos, D., Pirota, K. R., Garc ´ıa-Mart´ın, J. M. Nanometer scale hard/soft bilayer magnetic anti- dots. Nanoscale Res. Lett. 11, 86 (2016)

    work page 2016

  36. [36]

    63, 217 (2012)

    Kim, J.-V ., Spin-Torque Oscillators.Solid State Phys. 63, 217 (2012)

    work page 2012

  37. [37]

    & Pratt, W

    Bass, J. & Pratt, W. P. Spin-diffusion lengths in metals and alloys, and spin-flipping at metal/metal interfaces: an experimentalists critical review.J. Phys. Condens. Matter 19, 183201 (2007)

    work page 2007

  38. [38]

    Sagasta, E., Omori, Y ., Isasa, M., Otani, Y ., Hueso, L. E. & Casanova, F. Spin diffusion length of Permalloy using spin absorption in lateral spin valves. Appl. Phys. Lett. 111, 082407 (2017). 14 Acknowledgements We thank Dr. Muhammad Shahbaz Anwar for useful discussions. J.W.A. Robinson acknowledges funding from the Royal Society and the EPSRC through ...

    work page 2017