Magnetic proximity effect at the interface between a cuprate superconductor and an oxide spin valve
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ONIC PROPERTIES OF SOLID
Magnetic Proximity Effect at the Interface between a Cuprate Superconductor and an Oxide Spin Valve G. A. Ovsyannikova,b*, V. V. Demidova, Yu. N. Khaydukovc,d, L. Mustafac, K. Y. Constantiniana, A. V. Kalabukhovb,d, and D. Winklerb a Kotel’nikov
Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow, 125009 Russia b Chalmers University of Technology, Gothenburg, SE-41296 Sweden c Max Planck Institute for Solid State Research, Stuttgart, D-70569 Germany d Research Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received October 20, 2015
Abstract—A heterostructure that consists of the YBa2Cu3O7 – δ cuprate superconductor and the SrRuO3/La0.7Sr0.3MnO3 ruthenate/manganite spin valve is investigated using SQUID magnetometry, ferromagnetic resonance, and neutron reflectometry. It is shown that a magnetic moment is induced due to the magnetic proximity effect in the superconducting part of the heterostructure, while the magnetic moment in the composite ferromagnetic interlayer is suppressed. The magnetization emerging in the superconductor coincides in order of magnitude with the results of calculations taking into account the induced magnetic moment of Cu atoms because of orbital reconstruction at the interface between the superconductor and the ferromagnet, as well as with the results of the model taking into account the variations in the density of states at a distance on the order of the coherence length in the superconductor. The experimentally obtained characteristic penetration depth of the magnetic moment in the superconductor considerably exceeds the coherence length of the cuprate superconductor, which indicates the predominance of the mechanism of induced magnetic moment of Cu atoms. DOI: 10.1134/S1063776116040063
1. INTRODUCTION The penetration of ferromagnetic correlations into a superconductor (S) and of superconducting correlations into a ferromagnet (F), which is in contact with the superconductor, is currently attracting considerable attention from researchers [1, 2]. In the case of contact with normal metal, ferromagnetic correlations penetrate from the ferromagnet to normal metal to a small distance (on the order of atomic spacing) due to the local nature of the exchange interaction (see, e.g., [3]). It has been proved theoretically in [4–6] that the density of states in a superconductor at its interface with a ferromagnet changes under the action of the exchange field because the densities of states for electrons with spin up and spin down are different. Later, it was also shown theoretically that the sign and magnitude of the magnetic moment induced in the superconductor strongly depend on parameters of the S/F interface, such as its transparency, the presence of impurities, and the thickness of the layers [7–9]. The effect of parameters of the spin-active barrier at the S/F interface on the magnetic moment in the superconductor was analyzed theoretically in [10], and the emergence of an
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