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Proximity and flux pinning effects in superconductor-ferromagnet hybrids

Abstract : Superconductor-ferromagnet hybrid systems often bring about new physics and may as well be useful to design new non-volatile, high-density memory devices for superconducting electronics.In this thesis, we study two different types of SF hybrids, each following a possible approach to memory devices, but focusing on fundamental aspects. One is about the proximity effect in oxide heterostructures. In these, triplet correlations appear, that are both superconducting and spin-polarized. These enable using effects from spintronics like GMR, but are also very dependent on interface properties. We investigated these in SFS oxide trilayers by conductance measurements. These showed oscillations which may, in part, be related to these triplet states. We also observed that interface effects affect the electronic properties of the ferromagnet, especially when that layer is thin. Another type of interaction occurs through stray magnetic fields from the domain structures. Recent theoretical proposals suggested that small swirling spin textures called skyrmions could similarly interact with superconductivity through this mechanism. We investigated such coupling in bilayers, in which the superconducting vortex dynamics dominate the transport properties. We found that the presence of skyrmions and domains alike enhances the critical current. It also leads to an unusual Hall effect in the superconducting state. Most of these properties can be explained qualitatively in terms of vortex pinning and guided motion.
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Submitted on : Thursday, December 19, 2019 - 9:04:07 PM
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Xavier Palermo. Proximity and flux pinning effects in superconductor-ferromagnet hybrids. Superconductivity [cond-mat.supr-con]. Université Paris Saclay (COmUE), 2019. English. ⟨NNT : 2019SACLS231⟩. ⟨tel-02420472⟩

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