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Superconducting exchange coupling between ferromagnets

Abstract

Recent discoveries from superconductor (S)/ferromagnet (FM) heterostructures include π-junctions1, triplet pairing2,3, critical temperature (Tc) control in FM/S/FM superconducting spin valves (SSVs)4,5,6,7 and critical current control in S/FM/N/FM/S spin valve Josephson junctions8,9 (N: normal metal). In all cases, the magnetic state of the device, generally set by the applied field, controls the superconducting response. We report here the observation of the converse effect, that is, direct superconducting control of the magnetic state in GdN/Nb/GdN SSVs. A model10 for an antiferromagnetic effective exchange interaction based on the coupling of the superconducting condensation energy to the magnetic state can explain the Nb thickness and temperature dependence of this effect. This superconducting exchange interaction is fundamentally different in origin from the various exchange coupling phenomena that underlie conventional spin electronics (spintronics), and provides a mechanism for the active control of the magnetic state in superconducting spintronics11.

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Figure 1: Temperature dependence of spin valve effects in a GdN(3)/Nb(8)/GdN(5) heterostructure.
Figure 2: Influence of superconductor thickness on temperature-dependent coercive fields and spin valve effect in GdN/Nb/GdN heterostructures.
Figure 3: Superconductor-mediated antiferromagnetic exchange coupling in GdN/Nb/GdN SSVs.

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Acknowledgements

We thank J. W. A. Robinson and B. J. Hickey for valuable discussions. This work was supported by ERC AdG ‘Superspin’ and EPSRC Programme Grant EP/N017242/1.

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Authors

Contributions

Z.H.B. designed and coordinated the project, Y.Z. and A.P. designed and grew the samples and performed the measurements, M.G.B. developed the model. All authors contributed to writing the paper.

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Correspondence to Mark G. Blamire.

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The authors declare no competing financial interests.

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Zhu, Y., Pal, A., Blamire, M. et al. Superconducting exchange coupling between ferromagnets. Nature Mater 16, 195–199 (2017). https://doi.org/10.1038/nmat4753

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