Wachstum und Charakterisierung des Tunnelmagnetowiderstand-Mehrschichtsystems Co-Al 2 O 3 -CoAl und das Studium spinfrustrierter Vortices in Ringstrukturen
type: CreativeWork
description: This work discusses two major topics: The study of a Co-Al2O3-CoAl(100) TMR model system and the spin frustration in magnetic rings. CoAl(100) crystallizes in a CsCl-type structure. The scanning tunneling microscopy (STM) image displays flat and large terraces with a width of 40-100 nm separated by steps with a height of 0.28 nm. This agrees with the lattice constant of CoAl and represents a double atomic step of the CsCl structure. The ABAB stacking sequence is disturbed at the surface. The disturbance is caused by antisite atom segregation of Co atoms to the nominal Al sublattice in the topmost surface plane. Adsorption of O2 to the intermetallic alloy CoAl(100) allows the preparation of thin alumina films that can serve as a tunnel barrier in the tunneling magnetoresistance (TMR) model system. Exposure to oxygen at 300 K leads to the growth of amorphous oxide. The electron energy loss (EEL) spectra exhibit two losses at 640 und 890 cm-1. The self-limiting thickness of the amorphous alumina at saturation amounts to 0.7 nm. For this film a band gap of 3.7 eV was found. A new phenomenon shows up, namely the segregation-induced magnetism of CoAl(100). During the oxidation process Al segregates to the oxide-gas phase interface. The relative enrichment of Co in the crystal is sufficient to produce ferromagnetism of CoAl at 300 K. Oxidation at elevated temperatures leads to the growth of well-ordered alumina. At first, we study the oxidation at 800 K. The oxide is characterized by Fuchs-Kliewer modes at around 430, 630, 780 and 920 cm-1, which is indicative for the growth of a well-ordered oxide. LEED shows a two-domain (2x1) structure. We conclude that a well-ordered teta-Al2O3 grows on CoAl(100). Due to Al missing chains in the topmost layer STM exhibits streaks that are separated by 0.564 nm, which agrees with the lattice constant of the oxide. The thickness of the oxide film amounts to around 1 nm, and the band gap amounts to 4.4 eV. A thermal stability of the oxide…
abstract: This work discusses two major topics: The study of a Co-Al2O3-CoAl(100) TMR model system and the spin frustration in magnetic rings. CoAl(100) crystallizes in a CsCl-type structure. The scanning tunneling microscopy (STM) image displays flat and large terraces with a width of 40-100 nm separated by steps with a height of 0.28 nm. This agrees with the lattice constant of CoAl and represents a double atomic step of the CsCl structure. The ABAB stacking sequence is disturbed at the surface. The disturbance is caused by antisite atom segregation of Co atoms to the nominal Al sublattice in the topmost surface plane. Adsorption of O2 to the intermetallic alloy CoAl(100) allows the preparation of thin alumina films that can serve as a tunnel barrier in the tunneling magnetoresistance (TMR) model system. Exposure to oxygen at 300 K leads to the growth of amorphous oxide. The electron energy loss (EEL) spectra exhibit two losses at 640 und 890 cm-1. The self-limiting thickness of the amorphous alumina at saturation amounts to 0.7 nm. For this film a band gap of 3.7 eV was found. A new phenomenon shows up, namely the segregation-induced magnetism of CoAl(100). During the oxidation process Al segregates to the oxide-gas phase interface. The relative enrichment of Co in the crystal is sufficient to produce ferromagnetism of CoAl at 300 K. Oxidation at elevated temperatures leads to the growth of well-ordered alumina. At first, we study the oxidation at 800 K. The oxide is characterized by Fuchs-Kliewer modes at around 430, 630, 780 and 920 cm-1, which is indicative for the growth of a well-ordered oxide. LEED shows a two-domain (2x1) structure. We conclude that a well-ordered teta-Al2O3 grows on CoAl(100). Due to Al missing chains in the topmost layer STM exhibits streaks that are separated by 0.564 nm, which agrees with the lattice constant of the oxide. The thickness of the oxide film amounts to around 1 nm, and the band gap amounts to 4.4 eV. A thermal stability of the oxide…
author: Rose, Volker
language: ger
keywords: info:eu-repo/classification/ddc/530, Physik, Auger-Spektroskopie, Rastertunnelmikroskopie, Elektronen-Energieverlustspektroskopie, Magnetooptischer Kerr-Effekt, LEED, Flussschlauch, MFM, Oxidation, Al2O3, Vortex, CoAl
date published: 2005
date modified: 2026-07-30T19:42:56Z
provider: RWTH Aachen University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Publikationsserver der RWTH Aachen University