(Quelques) tendances et dfis du magntisme en dimensions rduites - PowerPoint PPT Presentation

(Quelques) tendances et défis du magnétisme en dimensions réduites Fondements et applications à l’électronique de spin O.Fruchart Laboratoire Louis Néel (CNRS-UJF-INPG) Grenoble Laboratoire Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Louis Néel, Grenoble, France. http://lab http:// lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

CNRS from mountains Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.2 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. http://lab http:// lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

Lab in mountains Part of the lab (Summer) Part of the lab (Summer) Part of the lab (Winter) Part of the lab (Winter) Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.3 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. http:// http://lab lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

TABLE OF CONTENTS 1. Introduction to magnetism and spintronics 2. Interfacial and coupling phenomena Magnetic anisotropy Magnetic coupling (dipolar, RKKY, F/AF) Thermal activation Fundamental effects fed into devices 3. Recent developments Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.4 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Louis Néel, Grenoble, France. Laboratoire http://lab http:// lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Currents, magnetic fields and magnetization Oersted field Magnetic moment Magnetic material µ µ = B 0 π 3 µ 4 r I = 0 B ⎡ ⎤ 3 π 2 r × − ( µ.r ) r µ ⎢ ⎥ Magnetization: A.m -1 2 ⎣ r ⎦ Magnetic moment: A.m 2 Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.5 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Louis Néel, Grenoble, France. Laboratoire http://lab http:// lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Hysteresis loops Manipulation of magnetic materials: � Application of a magnetic field = − µ E H.M Zeeman energy: Z 0 Spontaneous magnetization M s Remanent magnetization M r M M Coercive field H c Hext Hext Losses ∫ = µ E H d M 0 ext Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.6 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. http:// http://lab lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Magnetically soft and hard magnetic materials Soft materials Hard materials M M Hext Hext Transformers Flux guides Permanent magnets, motors Magnetic shielding Magnetic recording Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.7 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. http://lab http:// lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Sources of magnetic energy Echange energy Magnetocrystalline anisotropy energy = − E J S . S 1 2 Ech 1 , 2 M = ∇ θ 2 A ( ) = θ sin 2 E K ( ) mc Hext Zeeman energy (enthalpy) Dipolar energy 2 1 1 = − µ E M . H S d = − µ d 0 E M . H 2 S Z 0 Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.8 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Louis Néel, Grenoble, France. Laboratoire http:// http://lab lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Magnetic characteristic length scales Typical length scale: Bloch wall width λ B Numerical values λ = π A / K B λ = − λ B ≥ 2 3 nm 100 nm B Hard Soft ( ) 2 = θ + θ 2 e A d / dx K sin Exchange Anisotropy J/m 3 J/m Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.9 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. http://lab http:// lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Magnetization patterns Nanomagnetism ~ mesoscopic magnetism Bulk material Mesoscopic scale Nanometric scale Numerous and complex Small number of domains, Magnetic magnetic domains simple shape single-domain Microfabricated dots Co(1000) crystal – SEMPA Kerr magnetic imaging A. Hubert, Magnetic domains A. Hubert, Magnetic domains R.P. Cowburn, Magnetic recording essentially makes use of J.Phys.D:Appl.Phys.33, single-domain particles R1 (2000) Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.10 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Louis Néel, Grenoble, France. Laboratoire http:// http://lab lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Giant magnetoresistance Principle of GMR Discovery: 1988, A. Fert (CNRS-Thalès) and P. Grünberg (Jülich) Spin filtering in an heterostructure E Fermi level d d s s D(E) � Two-current model Features Applications ∆ R ∝ cos( θ ) • Magnetic sensors: compass, read heads Geometry: multilayers • Magnetic memory direct reading Magnitude: ≤ 40-50% Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.11 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Louis Néel, Grenoble, France. Laboratoire http:// http://lab lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Tunnelling magnetoresistance Principle of TMR Discovery: 1975 (Jullière); ‘rehabilitated’ 1995, Moodera et coll. • Spin filtering in heterostructures Ferro2 • Electron tunnelling between electrodes Insulator Ferro1 w Features ∆ R ∝ cos( θ ) E Geometry: multilayers E 0 eV Magnitude: ≤ 100-150% High resistance Ultrathin oxyde layer • Mécanique classique: pas de courant • Mécanique quantique: courant tunnel Applications • Magnetic sensors Équation de Schrödinger 2 2 d h − ψ + ψ = ψ • Magnetic memory direct V ( x ) E 2 2 m dx reading Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.12 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Louis Néel, Grenoble, France. Laboratoire http:// http://lab lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/

INTRODUCTION TO MAGNETISM – Magnetic recording : hard disks (media) Media: granular and columnar 200 nm Cr-rich Co-rich 40 nm Large number of grains per bit Grain : 10 nm CoPtCrTaB Disk Olivier Fruchart – JDN14 – Murol – May 14th, 2006 – p.13 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Louis Néel, Grenoble, France. Laboratoire http://lab http:// lab- -neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ /themes themes/couches/ /couches/ext ext/ /slides slides/ / http://lab-neel.grenoble.cnrs.fr/themes/couches/ext/slides/