DOCSLIB.ORG

Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies QUANG TUAN LE Doctoral Thesis in Physics School of Information and Communication Technology KTH Royal Institute of Technology Stockholm, Sweden 2016 KTH Royal Institute of Technology School of Information and Communication Technology TRITA-ICT 2016:21 SE-164 40 Kista ISBN 978-91-7729-072-8 SWEDEN Akademisk avhandling som med tillstånd av Kungl Tekniska högskolan framlägges till offentlig granskning för avläggande av teknologie doktorsexamen i Fysik fredagen den 30 sep 2016 klockan 13.00 i Sal C, Electrum, Kungl Tekniska högskolan, Kistagången 16, Kista. © Quang Tuan Le, August 2016 Tryck: Universitetsservice US-AB Abstract Spin-torque transfer (STT) effects have brought spintronics ever closer to practical electronic applications, such as MRAM and active broadband microwave spin-torque oscillator (STO), and have emerged as an increasingly attractive field of research in spin dynamics. Utilizing materials with perpendicular magnetic anisotropy (PMA) in such applications offers several great advantages such as low-current, low-field operation combined with high thermal stability. The exchange coupling that a PMA thin film exerts on an adjacent in-plane magnetic anisotropy (IMA) layer can tilt the IMA magnetization direction out of plane, thus creating a stack with an effective tilted magnetic anisotropy. The tilt angle can be engineered via both intrinsic material parameters, such as the PMA and the saturation magnetization, and extrinsic parameters, such as the layer thicknesses. STOs can be fabricated in one of a number of forms—as a nanocontact opening on a mesa from a deposited pseudospin-valve (PSV) structure, or as a nanopillar etching from magnetic tunneling junction (MTJ)—composed of highly reproducible PMA or predetermined tilted magnetic anisotropy layers. All-perpendicular CoFeB MTJ STOs showed high-frequency microwave generation with extremely high current tunability, all achieved at low applied biases. Spin-torque ferromagnetic resonance (ST-FMR) measurements and analysis revealed the bias dependence of spin-torque components, thus promise great potential for direct gate-voltage controlled STOs. In all-perpendicular PSV STOs, magnetic droplets were observed underneath the nanocontact area at a low drive current and low applied field. Furthermore, preliminary results for microwave auto-oscillation and droplet solitons were obtained from tilted-polarizer PSV STOs. These are promising and would be worth investigating in further studies of STT driven spin dynamics. Keywords: perpendicular magnetic anisotropy, tilted-polarizer, spintronics, STT, MTJ, pseudospin-valve, STO, ST-FMR, magnonics, magnetic droplet, droplet nucleation, droplet annihilation. iii Sammanfattning Effekter av spinnvridmoment (STT) har fört spinntroniken allt närmare praktiska elektroniska tillämpningar, såsom MRAM och den spinntroniska mikrovågsoscillatorn (STO), och har blivit ett allt mer attraktivt forskningsområde inom spinndynamik. Användning av material med vinkelrät magnetisk anisotropi (PMA) i sådana tillämpningar erbjuder flera stora fördelar, såsom låg strömförbrukning och funktion vid låga fält i kombination med hög termisk stabilitet. Den utbyteskoppling (”exchange bias”) en PMA-tunnfilm utövar på ett intilliggande skikt med magnetisk anisotropi i planet (IMA) kan få IMA-magnetiseringsriktningen att vridas ut ur planet, vilket ger en materialstack med en effektivt sett lutande magnetisk anisotropi. Lutningsvinkeln kan manipuleras med både inre materialparametrar, såsom PMA och mättningsmagnetisering, och yttre parametrar, såsom skikttjocklekarna. STO:er kan tillverkas som flera olika typer - som en nanokontaktsöppning på en s.k. mesa av en deponerad pseudospinnventilstruktur (PSV) eller som en nanotråd etsad ur en magnetisk tunnlingsövergång (MTJ) – och bestå av mycket reproducerbar PMA eller av skikt med på förhand bestämt lutning av dess magnetiska anisotropi. MTJ-STO:er av CoFeB med helt vinkelrät anisotropi visar högfrekvent mikrovågsgenerering med extremt stort frekvensomfång hos strömstyrningen, detta vid låg biasering. Mätning och analys av spinnvridmoments-ferromagnetisk resonans (ST-FMR) avslöjade ett biasberoende hos spinnvridmomentskomponenter, vilket indikerar en stor potential för direkt gate-spänningsstyrda STO:er. I helt vinkelräta PSV-STO:er observerades magnetiska droppar under nanokontaktområdet vid låg drivström och lågt pålagt fält. Dessutom erhölls preliminära resultat av mikrovågssjälvsvängning och av s.k. ”droplet solitons” hos PSV-STO:er med lutande polarisator. Dessa är lovande och skulle vara värda att undersökas i ytterligare studier av STT-driven spinndynamik. Nyckelord: vinkelrät magnetisk anisotropi, lutande polarisator, spinntronik, STT, MTJ, pseudospinnventil, STO, ST-FMR, magnonics, magnetisk droppe, nukleering av droppe, anihilering av droppe. iv Acknowledgement I am deeply grateful to my supervisor, Prof. Johan Åkerman, who was the one to give me the opportunity, to aid me getting it up and running; and showed your precious support all along to complete my projected research objectives. Also I would like to thank you very much, Johan, Maria, Hanna, Silas and Pontus, for creating and sharing joyful moments, which my family and I will never forget. Massive! To get this thesis printed, I would like to specifically thank Dr. Sun-Jae Chung. There have been many times my focus appeared to drift away and my motivation dissipated, every time you showed your tireless eagerness and passion to science that motivated and helped me getting a grip and pushing towards. Without you and your wholehearted efforts, I could not have it done. Magnificent! It is little wonder I could reach this significant milestone, given the knowledge and experience I benefited from the graduate Majid Mohseni and Sohrab Sani, as well as my current colleagues: Anders Eklund, Fatjon Qejvanaj, Hamid Mazraati, Sheng Jiang and Amir Banuazizi in Applied Spintronics group at KTH. A brief time working at NanOsc AB with Johan Persson and Fredrik Magnusson was valuable, too, and I am really appreciated. Influential! I have also got generous helps, in many ways, from scores of friends: Reza Nikpars, Magnus Lindberg, Himanshu Kataria, Cecillia Aronsson and Helena Strömberg (Acreo, IRnova, Ascatron); Christian Ridder, Per-Erik Hellström, Gabriel Roupillard, Yong-bin Wang, Tingsu Chen, Konstantinos Garidis, Ganesh Jayakumar, Arash Salemi, Hossein Elahipanah and Ahmad Abedin (EKT, ICT-KTH); Philipp Dürrenfeld, Afshin Houshang and Martina Ahlberg (Götenborgs Universitet); and technical supports from the Electrum staff, to work out my device processing inside KTH’s Electrum Fab and Chalmers’ MC2 Fab. Handy! The working environment is really enjoyable, thanks to Madeleine Printzsköld – my dedicated department administrator to simplify the related paperwork – and others along the corridor: Mats Göthelid, Sergei Popov, Ilya Sychugov, Markus Soldemo, Tobias Övergaard, Milad Yazdi, Roodabeh Afrasiabi, Federico Pevere, Shaozheng Ji, Yashar Hormozan, Miao Zhang, Viktor Jonsson and many others. Warm! v My sincere and lasting thanks are to all my beloved: Ngoc Anh, Ha Vy, Hoai Nam, my parents and parents-in-law, my brothers and sisters. This is the work I want to dedicate after your tremendous sacrifice and marvelous patience along the road. Your love, encouragement and tolerance invaluably helped to stiffen my back, harden my mind, and keep the strands of my life and work together. This little book marked the end of one chapter so a new chapter of life begins, but I always believe that I can count on you. Permanent! Tuan Le Stockholm – August 08, 2016 vi Table of Contents Abstract ...................................................................................... iii Acknowledgement ........................................................................ v Table of Contents........................................................................ vii List of Publications/Manuscripts ................................................ ix List of Acronyms and Symbols .................................................... xi 1. General introduction and thesis outline .................................. 1 2. Methodology ............................................................................ 5 2.1 Sputtering ............................................................................................. 5 2.2 Chemical vapor deposition .................................................................. 6 2.3 Evaluation of magnetic properties ...................................................... 7 2.4 Device fabrication procedure ............................................................... 8 2.5 Device measurement ........................................................................... 12 2.5.1 dc characterization ................................................................... 12 2.5.2 Microwave measurement ......................................................... 13 2.5.3 ST-FMR measurement and analytical model ......................... 13 3. Perpendicular magnetic anisotropic thin films.......................17 4. Spin dynamics in all-perpendicular MTJ STOs ...................... 21 4.1 Development of all-perpendicular MTJs ........................................... 21 4.2 Spin dynamics in all-perpendicular MTJ STOs ................................ 26 4.2.1 Device fabrication and dc characterization ............................ 26 4.2.2 Magnetodynamic
Load more

Recommended publications
  • Tunnel Magnetoresistance Angular and Bias Dependence
    www.nature.com/scientificreports OPEN Tunnel magnetoresistance angular and bias dependence enabling tuneable wireless communication Received: 21 August 2018 Ewa Kowalska1,2, Akio Fukushima3, Volker Sluka1, Ciarán Fowley 1, Attila Kákay1, Accepted: 20 June 2019 Yuriy Aleksandrov1,2, Jürgen Lindner1, Jürgen Fassbender1,2, Shinji Yuasa3 & Alina M. Deac1 Published: xx xx xxxx Spin-transfer torques (STTs) can be exploited in order to manipulate the magnetic moments of nanomagnets, thus allowing for new consumer-oriented devices to be designed. Of particular interest here are tuneable radio-frequency (RF) oscillators for wireless communication. Currently, the structure that maximizes the output power is an Fe/MgO/Fe-type magnetic tunnel junction (MTJ) with a fxed layer magnetized in the plane of the layers and a free layer magnetized perpendicular to the plane. This structure allows for most of the tunnel magnetoresistance (TMR) to be converted into output power. Here, we experimentally and theoretically demonstrate that the main mechanism sustaining steady- state precession in such structures is the angular dependence of the magnetoresistance. The TMR of such devices is known to exhibit a broken-linear dependence versus the applied bias. Our results show that the TMR bias dependence efectively quenches spin-transfer-driven precession and introduces a non-monotonic frequency dependence at high applied currents. This has an impact on devices seeking to work in the ‘THz gap’ due to their non-trivial TMR bias dependences. While initial spin-torque nano-oscillators (STNOs) studies focused on devices with fully in-plane (IP) magnet- ized magnetic layers1,2, hybrid device geometries combining an IP reference layer and an out-of-plane (OOP) magnetized free layer3,4 are now the system of choice in view of potential applications5–9.
    [Show full text]
  • The Development of Magnetic Tunnel Junction Fabrication Techniques
    The development of magnetic tunnel junction fabrication techniques Clifford Alastair Elwell Darwin College, Cambridge. A dissertation submitted for the degree of Doctor of Philosophy at the University of Cambridge July 2002 The development of magnetic tunnel junction fabrication techniques The discovery of large, room temperature magnetoresistance (MR) in magnetic tunnel junctions in 1995 sparked great interest in these devices. Their potential applications include hard disk read head sensors and magnetic random access memory (MRAM). However, the fabrication of repeatable, high quality magnetic tunnel junctions is still problematic. This thesis investigates methods to improve and quantify the quality of tunnel junction fabrication. Superconductor-insulator-superconductor (SIS) and superconductor-insulator- ferromagnet (SIF) tunnel junctions were used to develop the fabrication route, due to the ease of identifying their faults. The effect on SIF device quality of interchanging the top and bottom electrodes was monitored. The relationship between the superconducting and normal state characteristics of SIS junctions was investigated. Criteria were formulated to identify devices in which tunneling is not the principal conduction mechanism in normal metal-insulator-normal metal junctions. Magnetic tunnel junctions (MTJs) were produced on the basis of the fabrication route developed with SIS and SIF devices. MTJs in which tunneling is the principal conduction mechanism do not necessarily demonstrate high MR, due to effects such as magnetic coupling between the electrodes and spin scattering. Transmission electron microscope images were used to study magnetic tunnel junction structure, revealing an amorphous barrier and crystalline electrodes. The decoration of pinholes and weak-links by copper electrodeposition was investigated. A new technique is presented to identify the number of copper deposits present in a thin insulating film.
    [Show full text]
  • A Brief Review of Ferroelectric Control of Magnetoresistance in Organic Spin Valves Xiaoshan Xu University of Nebraska-Lincoln, [email protected]
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Xiaoshan Xu Papers Research Papers in Physics and Astronomy 2018 A brief review of ferroelectric control of magnetoresistance in organic spin valves Xiaoshan Xu University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/physicsxu Part of the Atomic, Molecular and Optical Physics Commons, Condensed Matter Physics Commons, and the Engineering Physics Commons Xu, Xiaoshan, "A brief review of ferroelectric control of magnetoresistance in organic spin valves" (2018). Xiaoshan Xu Papers. 11. https://digitalcommons.unl.edu/physicsxu/11 This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Xiaoshan Xu Papers by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. J Materiomics 4 (2018) 1e12 Contents lists available at ScienceDirect J Materiomics journal homepage: www.journals.elsevier.com/journal-of-materiomics/ A brief review of ferroelectric control of magnetoresistance in organic spin valves Xiaoshan Xu Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588, USA article info abstract Article history: Magnetoelectric coupling has been a trending research topic in both organic and inorganic materials and Received 16 September 2017 hybrids. The concept of controlling magnetism using an electric field is particularly appealing in energy Received in revised form efficient applications. In this spirit, ferroelectricity has been introduced to organic spin valves to 8 November 2017 manipulate the magneto transport, where the spin transport through the ferromagnet/organic spacer Accepted 11 November 2017 interfaces (spinterface) are under intensive study.
    [Show full text]
  • Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in Polycrystalline Co2feal Full-Heusler Alloy Magnetic Tunnel Junctions On
    Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates Zhenchao Wen, Hiroaki Sukegawa, Shinya Kasai, Koichiro Inomata, and Seiji Mitani National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047, Japan Abstract: We studied polycrystalline B2-type Co2FeAl (CFA) full-Heusler alloy based magnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate. Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a flat surface were achieved using a MgO buffer layer. A tunnel magnetoresistance (TMR) ratio up to 175% was obtained for an MTJ with a CFA/MgO/CoFe structure on a 7.5-nm-thick MgO buffer. Spin-transfer torque induced magnetization switching was achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a switching layer. Using a thermal activation model, the 6 2 intrinsic critical current density (Jc0) was determined to be 8.2 × 10 A/cm , which is lower than 2.9 × 107 A/cm2, the value for epitaxial CFA-MTJs [Appl. Phys. Lett. 100, 182403 (2012)]. We found that the Gilbert damping constant () evaluated using ferromagnetic resonance measurements for the polycrystalline CFA film was ~0.015 and was almost independent of the CFA thickness (2~18 nm). The low Jc0 for the polycrystalline MTJ was mainly attributed to the low of the CFA layer compared with the value in the epitaxial one (~0.04). 1 I. INTRODUCTION Half-metallic ferromagnets (HMFs) draw great interest because of the perfect spin polarization of conduction electrons at the Fermi level, which is considered to enhance the spin-dependent transport efficiency of high-performance spintronic devices.
    [Show full text]
  • Spin Polarized Current Phenomena in Magnetic Tunnel Junctions
    SPIN POLARIZED CURRENT PHENOMENA IN MAGNETIC TUNNEL JUNCTIONS A DISSERTATION SUBMITTED TO THE DEPARTMENT OF APPLIED PHYSICS AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Li Gao September 2009 © Copyright by Li Gao 2009 All Rights Reserved ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. _________________________________________________ (James S. Harris) Principal Advisor I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. _________________________________________________ (Stuart S. P. Parkin) co-Principal Advisor I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. _________________________________________________ (Walter A. Harrison) Approved for the University Committee On Graduate Studies. _________________________________________________ iii iv Abstract Spin polarized current is of significant importance both scientifically and technologically. Recent advances in film growth and device fabrication in spintronics make possible an entirely new class of spin-based devices. An indispensable element in all these devices is the magnetic tunnel junction (MTJ) which has two ferromagnetic electrodes separated by an insulator barrier of atomic scale. When electrons flow through a MTJ, they become spin-polarized by the first magnetic electrode. Thereafter, the interplay between the spin polarized current and the second magnetic layer manifests itself via two phenomena: i.) Tunneling magnetoresistance (TMR) effect.
    [Show full text]
  • Spin-Valve Effect in Nife/Mos2/Nife Junctions
    Spin-valve Effect in NiFe/MoS2/NiFe Junctions Weiyi Wang1,2, Awadhesh Narayan3,4, Lei Tang1, Kapildeb Dolui5, Yanwen Liu1,2, Xiang Yuan1,2, Yibo Jin1, Yizheng Wu1,2, Ivan Rungger3, Stefano Sanvito3, Faxian Xiu1,2, 1State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China 2Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433, China 3School of Physics, AMBER and CRANN Institute, Trinity College, Dublin 2, Ireland 4Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. 5Graphene Research Center and Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore Correspondence and requests for materials should be addressed to F.X. (E-mail: [email protected]) 1 Abstract Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have been recently proposed as appealing candidate materials for spintronic applications owing to their distinctive atomic crystal structure and exotic physical properties arising from the large bonding anisotropy. Here we introduce the first MoS2-based spin-valves that employ monolayer MoS2 as the nonmagnetic spacer. In contrast with what expected from the semiconducting band-structure of MoS2, the vertically sandwiched-MoS2 layers exhibit metallic behavior. This originates from their strong hybridization with the Ni and Fe atoms of the Permalloy (Py) electrode. The spin-valve effect is observed up to 240 K, with the highest magnetoresistance (MR) up to 0.73% at low temperatures. The experimental work is accompanied by the first principle electron transport calculations, which reveal an MR of ~ 9% for an ideal Py/MoS2/Py junction.
    [Show full text]
  • Pseudo Spin Valve Behavior in Colloidally Prepared Nanoparticle Films Benjamin H
    Letter Cite This: ACS Appl. Electron. Mater. 2019, 1, 1065−1069 pubs.acs.org/acsaelm Pseudo Spin Valve Behavior in Colloidally Prepared Nanoparticle Films Benjamin H. Zhou† and Jeffrey D. Rinehart*,†,‡ † ‡ Materials Science and Engineering Program and Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States *S Supporting Information ABSTRACT: Magnetoresistance provides a high-precision, versatile sensing mechanism that has continuously advanced in tandem with methods for top-down engineering of high-precision multilayer devices. Materials composed of solution-prepared nanocrystals can replicate some of the behavior of traditional magnetoresistive stacks but are limited by their intrinsic response mechanism: a gradual shift from low to high resistance with field. To fundamentally alter this behavior, we demonstrate the first instance of any form of spin valve behavior arising from a nanoparticle composite magnetoresistor. Single-layer films of varying CoFe2O4 to Fe3O4 nanoparticle ratios are used to show how the low-field sensitivity can be tuned to values exceeding those of either single-component material. Additionally, the sensitivity is shown to be a simple function of the magnetization of the individual component materials. KEYWORDS: colloidal nanomaterials, composite materials, spintronics, magnetoresistance, magnetism oon after the revolutionary discovery of giant magneto- Conversely, in a granular or nanocomposite magnetoresistor, S resistance (GMR) in multilayered structures,1,2 an application of an external magnetic field results in individual analogous effect was observed for magnetic grains in particle moments deviating from their original alignment with 3−7 Δ − conducting or insulating matrices. In this formulation, the the local anisotropy axes (maximum R/Rmax; Figure 1a ii,iv) matrix material acts as the spin-selecting junction between toward parallel alignment with the external field axis magnetically oriented grains, and the lack of structural (minimum ΔR/R; Figure1a−i,iii).
    [Show full text]
  • Spin-Dependent Transport in Antiferromagnetic Tunnel Junctions P
    Spin-dependent transport in antiferromagnetic tunnel junctions P. Merodio, A. Kalitsov, H. Béa, Vincent Baltz, M. Chshiev To cite this version: P. Merodio, A. Kalitsov, H. Béa, Vincent Baltz, M. Chshiev. Spin-dependent transport in anti- ferromagnetic tunnel junctions. Applied Physics Letters, American Institute of Physics, 2014, 105, pp.122403. 10.1063/1.4896291. hal-01683647 HAL Id: hal-01683647 https://hal.archives-ouvertes.fr/hal-01683647 Submitted on 19 May 2019 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. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. APPLIED PHYSICS LETTERS 105, 122403 (2014) Spin-dependent transport in antiferromagnetic tunnel junctions P. Merodio, 1, a) A. Kalitsov, 1,2 H. B ea, 1 V. Baltz, 1 and M. Chshiev 1, a) 1Univ. Grenoble Alpes, INAC-SPINTEC, F-38000 Grenoble, France; CNRS, SPINTEC, F-38000 Grenoble, France; and CEA, INAC-SPINTEC, F-38000 Grenoble, France 2MINT Center, University of Alabama, Box 870209, Tuscaloosa, Alabama 35487, USA (Received 8 July 2014; accepted 8 September 2014; published online 22 September 2014) We investigate the behaviour of spin transfer torque (STT) and tunnelling magnetoresistance (TMR) in epitaxial antiferromagnetic-based tunnel junctions using tight binding calculations in the framework of the Keldysh formalism.
    [Show full text]
  • Tunneling Magnetoresistance and Induced Domain Structure in Al 2 O 3 -Based Junctions M Hehn, O Lenoble, D Lacour, C Féry, M Piécuch, C Tiusan, K Ounadjela
    Tunneling magnetoresistance and induced domain structure in Al 2 O 3 -based junctions M Hehn, O Lenoble, D Lacour, C Féry, M Piécuch, C Tiusan, K Ounadjela To cite this version: M Hehn, O Lenoble, D Lacour, C Féry, M Piécuch, et al.. Tunneling magnetoresistance and induced domain structure in Al 2 O 3 -based junctions. Physical Review B, American Physical Society, 2000, 61 (17), pp.11643. 10.1103/PhysRevB.61.11643. hal-02954378 HAL Id: hal-02954378 https://hal.archives-ouvertes.fr/hal-02954378 Submitted on 1 Oct 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. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. PHYSICAL REVIEW B VOLUME 61, NUMBER 17 1 MAY 2000-I Tunneling magnetoresistance and induced domain structure in Al2O3-based junctions M. Hehn, O. Lenoble, D. Lacour, C. Fe´ry, and M. Pie´cuch Laboratoire de Physique des Mate´riaux, UMR CNRS 7556, Universite´ H. Poincare´–Nancy 1, Boıˆte Postale 239, 54506 Vandoeuvre Les Nancy Cedex, France C. Tiusan and K. Ounadjela Institut de Physique et de Chimie des Mate´riaux de Strasbourg, 23 rue du Loess, F-67037 Strasbourg Cedex, France ͑Received 1 July 1999; revised manuscript received 30 November 1999͒ Magnetization reversal in sputtered Co and oxidized Co ͑CoOx͒ layers are studied using transport measure- ments and magneto-optic Kerr effect.
    [Show full text]
  • Spin-Dependent Tunneling Spectroscopy in Single-Crystal Fe/Mgo/Fe Tunnel Junctions
    Spin-dependent tunneling spectroscopy in single-crystal Fe/MgO/Fe tunnel junctions 著者 安藤 康夫 journal or Applied Physics Letters publication title volume 87 page range 142502-1-142502-3 year 2005-10 URL http://hdl.handle.net/10097/34659 APPLIED PHYSICS LETTERS 87, 142502 ͑2005͒ Spin-dependent tunneling spectroscopy in single-crystal Fe/MgO/Fe tunnel junctions ͒ Y. Ando,a T. Miyakoshi, M. Oogane, and T. Miyazaki Graduate School of Engineering, Tohoku University, 6-6-05 Aoba-yama, Sendai 980-8579, Japan ͒ H. Kubota, K. Ando, and S. Yuasab National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba 305-8568, Japan ͑Received 11 April 2005; accepted 9 August 2005; published online 27 September 2005͒ We report a detailed spin-dependent tunneling spectroscopy in single-crystal Fe͑001͒/MgO͑001͒/Fe͑001͒ magnetic tunnel junctions ͑MTJs͒ that show a giant tunnel magnetoresistance effect. Spectra for antiparallel magnetic configurations show asymmetry because of extrinsic electron scatterings caused by structural defects at the barrier/electrode interfaces. Surprisingly, spectra for parallel magnetic configurations exhibit a complex oscillatory structure that has never been observed in conventional MTJs with an aluminum-oxide tunnel barrier. The complex spectra reflect the tunneling process via interface resonant states. These results provide some information that helps to elucidate the physics of spin-dependent electron tunneling and to further enhance magnetoresistance. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2077861͔ Recent progress of a giant tunnel magnetoresistance scopic study of the single-crystal MTJs is important for clari- ͑TMR͒ effect in magnetic tunnel junctions ͑MTJs͒ with a fying the controversial physical mechanism of spin- MgO͑001͒ tunnel barrier1–4 promises the promotion of in- dependent tunneling.
    [Show full text]
  • Detection of Small Magnetic Fields Using Serial Magnetic Tunnel Junctions with Various Geometrical Characteristics
    sensors Letter Detection of Small Magnetic Fields Using Serial Magnetic Tunnel Junctions with Various Geometrical Characteristics Zhenhu Jin 1,*, Yupeng Wang 1, Kosuke Fujiwara 2, Mikihiko Oogane 1,3,4 and Yasuo Ando 1,3,4 1 Department of Applied Physics, Tohoku University, Sendai 980–8579, Japan; [email protected] (Y.W.); [email protected] (M.O.); [email protected] (Y.A.) 2 Spin Sensing Factory Corporation, Sendai 980–0845, Japan; [email protected] 3 Center for Science and Innovation in Spintronics (Core Research Cluster), Tohoku University, Sendai 980–8577, Japan 4 Center for Spintronics Research Network, Tohoku University, Sendai 980–8579, Japan * Correspondence: [email protected] Received: 11 September 2020; Accepted: 2 October 2020; Published: 7 October 2020 Abstract: Thanks to their high magnetoresistance and integration capability, magnetic tunnel junction-based magnetoresistive sensors are widely utilized to detect weak, low-frequency magnetic fields in a variety of applications. The low detectivity of MTJs is necessary to obtain a high signal-to-noise ratio when detecting small variations in magnetic fields. We fabricated serial MTJ-based sensors with various junction area and free-layer electrode aspect ratios. Our investigation showed that their sensitivity and noise power are affected by the MTJ geometry due to the variation in the magnetic shape anisotropy. Their MR curves demonstrated a decrease in sensitivity with an increase in the aspect ratio of the free-layer electrode, and their noise properties showed that MTJs with larger junction areas exhibit lower noise spectral density in the low-frequency region.
    [Show full text]
  • Characterization of Magnetic Tunnel Junctions for Next-Generation Energy-Efficient Memory Technologies
    CALIFORNIA STATE SCIENCE FAIR 2015 PROJECT SUMMARY Name(s) Project Number Raymond U. Gilmartin S1710 Project Title Characterization of Magnetic Tunnel Junctions for Next-Generation Energy-Efficient Memory Technologies Abstract Objectives/Goals Magnetoresistive random-access memory (MRAM) combines fast read/write time, high endurance, and nonvolatile storage. Magnetoelectric RAM (MeRAM), a new class of MRAM, uses voltage-controlled magnetic anisotropy (VCMA) and high resistance-area product (RA) to lower coercivity and limit the writing current when changing the polarity of the ferromagnetic layers in a magnetic tunnel junction (MTJ). High tunnel magnetoresistance (TMR) enables the resistance-state of an MTJ to be read accurately with greater tolerance and thus less sensitive, less expensive reading devices. The objective of this project is to characterize the relationship between TMR and RA to improve energy-efficiency and lower cost. Methods/Materials Using sputtering deposition and photolithography, MTJs were fabricated with an MgO insulator layer of graduated thickness between conductive Co(40)Fe(40)B(20) ferromagnetic layers. Ta buffer layers develop perpendicular magnetic anisotropy and a Pt cap prevents unwanted oxidation. To determine TMR and RA, the voltage across each MTJ was measured with a four-point DC probe station using a 0.01 mA current and a magnetic field sweeping between ±600 Oe. Results TMR has a maximum for MgO thickness, indicating optimal oxidation: peak TMR occurs when the MgO layer is oxidized and insulating and the CoFeB layers are un-oxidized and conducting. RA values increase exponentially with MgO thickness and are nearly identical across MTJ sizes, reflecting both the exponentially decreasing electron wave amplitude in the insulator and the resistance-resistivity relationship.
    [Show full text]