Dynamical spin injection and spin to charge current conversion in oxide-based Rashba interfaces and topological insulators Paul Noel To cite this version: Paul Noel. Dynamical spin injection and spin to charge current conversion in oxide-based Rashba interfaces and topological insulators. Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes- hall]. Université Grenoble Alpes, 2019. English. NNT : 2019GREAY062. tel-02619764 HAL Id: tel-02619764 https://tel.archives-ouvertes.fr/tel-02619764 Submitted on 25 May 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. 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THÈSE Pour obtenir le grade de DOCTEUR DE LA COMMUNAUTE UNIVERSITE GRENOBLE ALPES Spécialité : Physique de la matière condensée Arrêté ministériel : 25 mai 2016 Présentée par Paul NOËL Thèse dirigée par Jean-Philippe ATTANÉ, UGA et codirigée par Laurent VILA, CEA préparée au sein du Laboratoire Spintronique et Technologie des Composants (SPINTEC) et de l'École Doctorale de Physique de Grenoble Dynamical spin injection and spin to charge current conversion in oxide-based Rashba interfaces and topological insulators Thèse soutenue publiquement le « 14/11/2019 », devant le jury composé de : Mme, Stefania, PIZZINI Directrice de recherche, Institut Néel, Présidente du jury Mr, Michel, VIRET Chercheur CEA Saclay, laboratoire SPEC, Rapporteur Mr, Pietro, GAMBARDELLA Professeur, ETH Zurich, Department of materials, Rapporteur Mr, Abdelmadjid, ANANE Enseignant-Chercheur, Université Paris-Sud, Examinateur Mr, Dafiné, RAVELOSONA Directeur de recherche, C2N, Examinateur Mr, Manuel, BIBES Directeur de recherche, CNRS Thales, Membre invité 2 Table of contents Introduction 6 1 Spin current to charge current interconversion by spin orbit coupling 12 1.1 Spin currents and charge currents ............................ 12 1.1.1 Characteristic lengths .............................. 12 1.1.2 Two currents model ............................... 14 1.2 Spin Hall Effect ..................................... 16 1.2.1 Intrinsic Spin Hall Effect ............................ 17 1.2.2 Extrinsic Spin Hall Effect ........................... 18 1.3 Rashba-Edelstein Effect at surfaces and interfaces ................... 20 1.3.1 Rashba two dimensional electron gases and Topological surface states .... 20 1.3.2 Direct and inverse Rashba-Edelstein Effect .................. 23 2 Spin pumping by ferromagnetic resonance 29 2.1 Ferromagnetic Resonance ................................ 29 2.1.1 Landau-Lifschitz-Gilbert equation ....................... 29 2.1.2 Ferromagnetic resonance conditions ...................... 31 2.2 FMR: a powerful magnetometry tool .......................... 36 2.2.1 Broadband FMR: frequency dependence .................... 36 2.2.2 FMR in cavity: angular dependence at X-band ................ 38 2.3 Spin transfer via spin pumping by ferromagnetic resonance .............. 45 2.3.1 Origin of the spin injection ........................... 46 2.3.2 Spin current expression ............................. 48 2.3.3 Evaluation of spin charge interconversion efficiency ............. 51 2.4 Disentangling ISHE/IEE from spurious effects ..................... 55 2.4.1 Spin pumping ISHE/IEE angular dependence ................. 55 2.4.2 Spin Rectification Effects ........................... 56 2.4.3 Thermal effects? ................................ 61 3 Spin Hall effect in heavy metals and Alloys 64 3.1 Spin Hall effect in pure metals: Pt, Ta and W ...................... 64 3.1.1 Positive or negative spin hall angle? ...................... 65 3.1.2 Stacking order dependence ........................... 66 3.2 A possible thermal contribution? ............................ 67 3.2.1 Lack of Universal method to evaluate the thermal related effects ....... 68 3.2.2 Spin Pumping experiment ........................... 69 3.2.3 Temperature increase and spin signal: a different timescale .......... 70 3 3.2.4 Differences in the timescale: further evidences ................ 71 3.3 Spin Hall Effect in Au based alloys ........................... 75 3.3.1 Sample fabrication ............................... 75 3.3.2 Methods .................................... 76 3.3.3 Spin diffusion length and spin Hall angle in AuW ............... 77 3.3.4 Spin diffusion length and spin Hall angle in AuTa ............... 79 4 Rashba Edelstein effect at oxide heterointerfaces 82 4.1 A two dimensional electron gas at the surface of STO ................. 82 4.1.1 A 2DEG with appealing properties for spintronics ............... 83 4.1.2 STO\Al: no need of LAO ............................ 84 4.1.3 STO 2DEG: a complex bandstructure ..................... 87 4.2 Spin to charge conversion in STO\Al\Py structure ................... 90 4.2.1 Mapping to the bandstructure ......................... 90 4.2.2 Role of the insulating barrier .......................... 94 4.2.3 Spin to charge interconversion at room temperature .............. 96 4.3 Ferroelectricity in STO: non volatile switching of the IEE ............... 97 4.3.1 Ferroelectric STO? ............................... 98 4.3.2 Remanent modulation of the spin to charge conversion ............ 101 4.3.3 Modulation of the 2DEG by ferroelectricity .................. 105 4.3.4 Possible memory and logic applications .................... 109 5 Edelstein effect in topological insulators 112 5.1 An efficient spin to charge conversion in strained HgTe ................ 112 5.1.1 Tensile strained HgTe on CdTe: a 3D topological insulator .......... 113 5.1.2 Sample preparation ............................... 115 5.1.3 Spin to charge conversion: role of the HgCdTe barrier ............ 115 5.1.4 Spin to charge conversion: role of the HgTe thickness ............. 119 5.2 Sb2T e3: a sputtered deposited topological insulator material ............. 123 5.2.1 Sputtering: an industry compatible process .................. 123 5.2.2 High quality thin films ............................. 124 5.2.3 Magnetotransport: Weak Antilocalization ................... 127 5.2.4 Spin to charge interconversion ......................... 131 Conclusion 134 Acknowledgment 139 Bibliography 142 A FMR cavity: Brucker MS5 loop gap 164 B Offset signal associated with the temperature increase 167 4 C Change of the magnetic properties of the ferromagnet with the applied power 170 D Gate voltage dependence of the ferromagnetic resonance lineshape in STO \CFB 176 E Sb2T e3 ultrathin films and stoichiometry 179 5 Introduction During the last fifty years the available processing power has evolved exponentially, thanks to the ag- gressive scaling down of transistors down to 10 nm or less1. This exponential downscaling has been accompanied by an exponential decrease of the power consumption and of the manufacturing costs, as well as an increase of the available processing power, following what is known as Moore’s law2. While still valid today, this exponential scaling is now approaching physical limits3. In order to li- mit the power consumption of information and communication technology, that now represents more than 4% of the worldwide power consumption4, and to promote novel computing schemes for better processing capabilities, new routes need to be explored. Beyond the scaling down of transistors and improved architectures, the field of spin-electronics or spintronics appears as a particularly appealing path in the quest of an electronic beyond Moore’s law. Thanks to the intimate interaction of the electronic and magnetic structures with spin currents, spin- tronics allow novel ways to process information and store datas. The remanence associated with magnetization and the ability to switch it in hundreds of picoseconds makes it possible to obtain fast non-volatile devices. Moreover, it allows reducing the energy needed for information storage, as the data remain stored in absence of any power input. Spintronics also open novel routes for processing units, including logic in memory architectures or majority gate circuits5;6. From Conventional spintronics Although efforts on the understanding of various spin effects such as the Anomalous Hall Effect or the Anisotropic Magnetoresistance have been made since the 1950’s7 the birth of modern spintro- nics is usually associated with the independent discovery of the giant magnetoresistance (GMR) by the groups of Albert Fert and Peter Gründberg in 19888;9. This magnetoresistive effect appears in ferromagnetic\normal metal\ferromagnetic (FM\NM\FM) layers, and allows to obtain different levels of resistance depending on the relative magnetization direction of the two ferromagnetic layers10. Therefore, the resistance of this structure is sensitive to an external magnetic field. This effect permit- ted the development of a wide variety of sensors, such as read-heads for hard-disk drives. Those all metallic GMR devices were further replaced by magnetic tunnel junctions where the non magnetic metallic layer is an insulator11. In these junctions the tunnelling magnetoresistance (TMR) can reach hundreds of percent, compared to some dozens of percent for GMR devices12. Thanks to this higher change of resistance, magnetic