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Interface morphology effect on the spin mixing conductance of Pt/Fe3O4 bilayers

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      Abstract

      Non-magnetic (NM) metals with strong spin-orbit coupling have been recently explored as a probe of interface magnetism on ferromagnetic insulators (FMI) by means of the spin Hall magnetoresistance (SMR) effect. In NM/FMI heterostructures, increasing the spin mixing conductance (SMC) at the interface comes as an important step towards devices with maximized SMR. Here we report on the study of SMR in Pt/Fe3O4 bilayers at cryogenic temperature, and identify a strong dependence of the determined real part of the complex SMC on the interface roughness. We tune the roughness of the Pt/Fe3O4 interface by controlling the growth conditions of the Fe3O4 films, namely by varying the thickness, growth technique, and post-annealing processes. Field-dependent and angular-dependent magnetoresistance measurements sustain the clear observation of SMR. The determined real part of the complex SMC of the Pt/Fe3O4 bilayers ranges from 4.96 × 1014 Ω−1 m−2 to 7.16 × 1014 Ω−1 m−2 and increases with the roughness of the Fe3O4 underlayer. We demonstrate experimentally that the interface morphology, acting as an effective interlayer potential, leads to an enhancement of the spin mixing conductance.

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      Most cited references 33

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      Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection.

      Modern computing technology is based on writing, storing and retrieving information encoded as magnetic bits. Although the giant magnetoresistance effect has improved the electrical read out of memory elements, magnetic writing remains the object of major research efforts. Despite several reports of methods to reverse the polarity of nanosized magnets by means of local electric fields and currents, the simple reversal of a high-coercivity, single-layer ferromagnet remains a challenge. Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay of data storage media, owing to their ability to retain a stable magnetization state over long periods of time and their amenability to miniaturization. However, the same anisotropy properties that make a material attractive for storage also make it hard to write to. Here we demonstrate switching of a perpendicularly magnetized cobalt dot driven by in-plane current injection at room temperature. Our device is composed of a thin cobalt layer with strong perpendicular anisotropy and Rashba interaction induced by asymmetric platinum and AlOx interface layers. The effective switching field is orthogonal to the direction of the magnetization and to the Rashba field. The symmetry of the switching field is consistent with the spin accumulation induced by the Rashba interaction and the spin-dependent mobility observed in non-magnetic semiconductors, as well as with the torque induced by the spin Hall effect in the platinum layer. Our measurements indicate that the switching efficiency increases with the magnetic anisotropy of the cobalt layer and the oxidation of the aluminium layer, which is uppermost, suggesting that the Rashba interaction has a key role in the reversal mechanism. To prove the potential of in-plane current switching for spintronic applications, we construct a reprogrammable magnetic switch that can be integrated into non-volatile memory and logic architectures. This device is simple, scalable and compatible with present-day magnetic recording technology.
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        Observation of the spin Seebeck effect.

         K Ando,  E. Saitoh,  J Ieda (2008)
        The generation of electric voltage by placing a conductor in a temperature gradient is called the Seebeck effect. Its efficiency is represented by the Seebeck coefficient, S, which is defined as the ratio of the generated electric voltage to the temperature difference, and is determined by the scattering rate and the density of the conduction electrons. The effect can be exploited, for example, in thermal electric-power generators and for temperature sensing, by connecting two conductors with different Seebeck coefficients, a device called a thermocouple. Here we report the observation of the thermal generation of driving power, or voltage, for electron spin: the spin Seebeck effect. Using a recently developed spin-detection technique that involves the spin Hall effect, we measure the spin voltage generated from a temperature gradient in a metallic magnet. This thermally induced spin voltage persists even at distances far from the sample ends, and spins can be extracted from every position on the magnet simply by attaching a metal. The spin Seebeck effect observed here is directly applicable to the production of spin-voltage generators, which are crucial for driving spintronic devices. The spin Seebeck effect allows us to pass a pure spin current, a flow of electron spins without electric currents, over a long distance. These innovative capabilities will invigorate spintronics research.
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          Spin Hall effects

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            Author and article information

            Affiliations
            [1 ]ISNI 0000 0001 2171 7754, GRID grid.255649.9, Center for Quantum Nanoscience, Institute for Basic Science, , Ewha Womans University, ; Seoul, 03760 Korea
            [2 ]ISNI 0000 0001 2171 7754, GRID grid.255649.9, Department of Physics, , Ewha Womans University, ; Seoul, 03760 Korea
            [3 ]ISNI 0000 0000 9149 5707, GRID grid.410885.0, Spin Engineering Physics Team, , Division of Scientific Instrumentation, Korea Basic Science Institute, ; Daejeon, 34133 Korea
            [4 ]ISNI 0000 0001 1364 9317, GRID grid.49606.3d, Division of Materials Science & Engineering, , Hanyang University, ; Seoul, 04763 Korea
            [5 ]ISNI 0000 0001 0840 2678, GRID grid.222754.4, KU-KIST Graduate School of Converging Science and Technology, , Korea University, ; Seoul, 02841 Korea
            [6 ]ISNI 0000 0004 0533 4667, GRID grid.267370.7, Department of Physics and Energy Harvest Storage Research Center, , University of Ulsan, ; Ulsan, 44610 Korea
            [7 ]ISNI 0000 0001 2164 3230, GRID grid.462224.4, Départment de Physique et Mécanique des Matériaux, , Institut Pprime, UPR 3346, CNRS-Université de Poitiers-ENSMA, ; Poitiers, France
            Contributors
            ORCID: http://orcid.org/0000-0002-3588-0146, taehee@ewha.ac.kr
            Journal
            Sci Rep
            Sci Rep
            Scientific Reports
            Nature Publishing Group UK (London )
            2045-2322
            17 September 2018
            17 September 2018
            2018
            : 8
            30224773
            6141513
            31915
            10.1038/s41598-018-31915-3
            © The Author(s) 2018

            Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

            Funding
            Funded by: Institute for Basic Science, Republic of Korea (IBS-R027-D1)
            Funded by: the National Research Council of Science & Technology (NST) grant (No. CAP-16-01-KIST).
            Funded by: Institute for Basic Science, Republic of Korea (IBS-R027-D1).
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