Spin resolved photoelectron spectroscopy of oxidic half metallic ferromagnets and oxide,ferromagnet interfaces [Elektronische Ressource] / vorgelegt von Yuriy Dedkov

Sujets

• Physik

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2004
• Nombre de lectures: 12
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

Spin-Resolved Photoelectron Spectroscopy of
Oxidic Half-Metallic Ferromagnets and
Oxide/Ferromagnet Interfaces








Von der Fakultät für Mathematik, Informatik und Naturwissenschaften
der Rheinisch-Westfälischen Technischen Hochschule Aachen zur Erlangung des
akademischen Grades eines Doktors der Naturwissenschaften genehmigte Dissertation

vorgelegt von
Master of Science

Yuriy Dedkov

aus Novgorod (Russland)





Berichter: Universitätsprofessor Dr. G. Güntherodt
Universitätsprofessor Dr. U. Rüdiger




Tag der mündlichen Prüfung: 06.02.2004







Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar.
Contents

1. Introduction....................................................................................................... 1
2. Theoretical and Technical Basis....... 3
2.1. Oxide/Ferromagnet Interface. 3
2.1.1. Magnetic Random Access Memory (MRAM)............................ 3
2.1.2. Tunnelling Magnetoresistance (TMR)........................................ 6
2.1.3. Growth of Thin Al O Films on Metal and Metal Alloy 2 3
Surfaces....................................................................................... 14
2.2. Half-Metallic Ferromagnets (HMF)...................... 19
2.2.1. HMFs: an Overview.................................................................... 19
2.2.2. Fe O (Magnetite)....... 23 3 4
2.2.2.1. Crystallographic Structure of Fe O ........................... 23 3 4
2.2.2.2. Electronic Band Structure of Fe O ............................ 25 3 4
2.2.2.3. Transport Properties of Fe O .................................... 27 3 4
2.2.2.4. Optical and Magneto-Optical Properties of Fe O ..... 28 3 4
2.2.2.5. Photoelectron Spectroscopy Experiments
on Fe O 30 3 4 .........................................................................................................
2.2.3.CrO (Chromium Dioxide) ......................................................... 35 2
2.2.3.1. Crystallographic Structure of CrO ............................ 35 2
2.2.3.2. Electronic Band Structure of CrO ............................. 37 2
2.2.3.3. Spectroscopic Determination of the Spin
Polarization of CrO ................................................... 42 2
2.3. General Aspects of Photoemission Spectroscopy (PES) ....................... 46
2.3.1. Phenomenology........................................... 46
2.3.2. Single-Particle Aspects of PES................................................... 49
2.3.3. Deviation from the Single-Particle Picture................................. 52
2.3.4. Principles and Techniques of Spin-Resolved PES ..................... 53
2.3.5. Experimental Setup for Spin- and Angle-Resolved
Photoemission Spectroscopy....................................................... 56
2.3.6. Experimental Setup for Angle Resolved Photoemission
Spectroscopy at BESSY II.......................... 58
i 3. Spin- and Angle-Resolved Photoemission Spectroscopy Study of HMFs:
Fe O and CrO ................................................................................................. 60 3 4 2
3.1. Fe O (111)............................. 61 3 4
3.1.1. Growth and Crystallographic Structure of Fe O (111)............... 61 3 4
3.1.2. Spin- and Angle-Resolved Photoemission of Fe O (111).......... 64 3 4
3.1.3. Angle-Resolved Photoemission of Fe O (111) at BESSY II ..... 70 3 4
3.2. CrO (100)............................................................................................... 78 2
3.2.1. Growth and Characterization of CrO (100) Films...................... 78 2
3.2.2. Spin- and Angle-Resolved Photoemission of CrO (100) ........... 82 2
4. Spin-Resolved Photoemission of a-Al O (0001)/Fe(110) and MgO/Fe(110) . 89 2 3
4.1. General Overview.................................................................................. 89
4.2. Growth and Characterization of a-Al O /Fe(110) Bilayers 90 2 3
4.3. Spin-Resolved Photoelectron Spectroscopy of a-Al O /Fe(110) 2 3
Bilayers .................................................................................................. 95
4.4. Growth and Characterization of MgO/Fe(110) Bilayers ....................... 97
4.5. Spin-Resolved Photoelectron Spectroscopy of MgO/Fe(110) Bilayers 100
5. Conclusion ........................................................................................................ 106
Appendix...................... 108
References.................................................................................................................... 110
List of Publications...... 122
Acknowledgements...................................................................................................... 125
Curriculum vitae.......... 127
Zusammenfassung....... 128

ii AES Auger Electron Spectroscopy
AFMAtomic Force Microscopy
AMR Anisotropic Magneto-Resistance
APWAugmented Plane Wave
ARPES Angle-Resolved Photoelectron Spectroscopy
ASW Augmented Spherical Wave
CI Configuration Interaction
CVD Chemical Vapor Deposition
DRAM Dynamic Random Access Memory
DOS Density of States
E Fermi Energy F
FM Ferromagnet
GGA Generalized Gradient Approximation
HMF Half-Metallic Ferromagnet
HREELS High-Resolution Electron Energy Loss Spectroscopy
IMFP Inelastic Mean Free Path
-6L Langmuir (1L=1?10 mbar?sec)
LAPW Linearised Augmented Plane-Wave Method
LEED Low-Energy-Electron Diffraction
LEISLow-Energy Ion Scattering
LMTO-ASA Linear Muffin-Tin Orbitals Methods in the Atomic Spheres
Approximation
LSDA Local Spin-Density Approximation
MBEMolecular-Beam-Epitaxy
ML Monolayer
MO Magneto-Optical Spectroscopy
MOKE Magneto-Optical Kerr Effect
MR Magnetoresistance
MRAM Magnetic Random Access Memory
MTJ Magnetic Tunnel Junction
PCAR Point-Contact Andreev Reflection Technique
PES Photoelectron Spectroscopy
SBZ Surface Brillouin Zone
SICF Single-Ion-in-a-Crystal-Field Model
SPARPES Spin-Polarized Angle-Resolved Photoelectron Spectroscopy
SQUID Superconducting Quantum Interferometer Device
STM Scanning Tunneling Microscopy
TEMTransmission Electron Microscopy
TMO Transition-Metal Oxides
TMRTunneling Magnetoresistance
UHV Ultra-High Vacuum
XPDX-ray Photoelectron Diffraction
XPS X-ray Photoelectron Spectroscopy

iii 1. Introduction
1. Introduction

In recent years there has been a significant increase in research activities in the
area of half-metallic ferromagnets and device components on the basis of such
materials. The basic property of half-metallic ferromagnets is one metallic spin
channel whereas the other one is semiconducting or insulating. In such materials for
both scientific and technological reasons it is of importance to measure the spin
polarization and the spin-resolved electronic structure near the Fermi energy, E , in F
order to verify the half-metallic nature of the electronic band structure.
Unfortunately, from an experimental point of view the determination of the spin
polarization at the Fermi energy of such materials is still a challenging task. A typical
transition-metal ferromagnet has two dominating components to its electronic
structure: narrow d bands that may be fully or partially spin-polarized and broad s
bands with a lesser degree of spin polarization (due to the hybridization with d bands).
Spin polarization measurements require a spectroscopic technique that can
discriminate between the spin-up and spin-down electrons near the Fermi energy. One
of the well established methods is the spin-resolved photoelectron spectroscopy
technique.
The present work is a detailed experimental analysis of the crystal growth as
well as of the electronic structure of single crystalline Fe O and CrO thin films by 3 4 2
means of spin-resolved photoelectron spectroscopy, which are predicted to be half-
metallic ferromagnets.
The second chapter gives an overview about the theoretical and present
experimental background concerning the field of half-metallic ferromagnets. This part
also includes the state-of-the-art developments in magnetic random access memory
devices and describes the potential of half-metallic ferromagnets for the efficiency of
such memory devices. The theoretical and technical problems which are important for
the understanding of the physical properties of magnetoelectronic devices are also
described in the second chapter.
The third chapter consists of the experimental results concerning the
investigations of half-metallic ferromagnets: magnetite and chromium dioxide. In this
part the growth and the magnetic properties of these materials are discussed. The spin-
1 1. Introduction
resolved photoelectron spectroscopy investigations of these half-metallic materials
show a high spin polarization near the Fermi energy. The treatment of spin-resolved
photoelectron spectra was made on the basis of band structure calculations that show a
good agreement