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Structural coherence and layer perfection in Fe/MgO multilayers
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
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2008 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 5, 055212- p.Article in journal (Refereed) Published
Abstract [en]

A series of Fe/MgO multilayers was grown on single-crystal MgO(001) substrates at different temperatures using magnetron sputtering. The structural quality of the samples was investigated by x-ray reflectometry, x-ray diffraction and transmission electron microscopy. The results show a strong dependence of the structural quality on the growth temperature. Although good epitaxial layers are obtained at 165 ◦C, the sample does not exhibit any superlattice diffraction peaks. This effect is shown to be related to a continuous variation of the distance between the Fe layers as well as between the MgO layers.

Place, publisher, year, edition, pages
2008. Vol. 20, no 5, 055212- p.
National Category
Physical Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-13627DOI: 10.1088/0953-8984/20/5/055212ISI: 000252923400015OAI: oai:DiVA.org:uu-13627DiVA: diva2:41397
Available from: 2008-01-24 Created: 2008-01-24 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Tailoring Properties of Materials at the Nanoscale
Open this publication in new window or tab >>Tailoring Properties of Materials at the Nanoscale
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The knowledge of growth and characterizing techniques is essential for the preparation of high quality thin films and multilayers. Here, structural properties have been investigated by X-ray reflectivity, X-ray diffraction, and transmission electron microscopy while the composition was determined by Rutherford backscattering spectrometry. For the magnetic studies, magneto-optical Kerr effect and X-ray magnetic circular dichroism have been used.

The structural properties of the metal/insulator multilayer system, Fe/MgO, have been investigated. The coherency of the layers was influenced by the difference of the atomic distance in the Fe and MgO layers, resulting in long range strain fields. As a consequence, the coherency between the layers is not maintained.

The atomic steps can not exist in amorphous materials, due to the absence of well defined atomic distances. Furthermore, the magnetic properties of amorphous materials allow a tuning of magnetic properties such as magnetic anisotropy and ordering temperature. The possibility to imprint arbitrary magnetic anisotropy in nanolaminated magnetic amorphous Co68Fe24Zr8 was demonstrated. The ratio of the orbital to spin moments for both Fe and Co was determined, for both thick and thin layers embedded in amorphous Al70Zr30 layers. When growing Co68Fe24Zr8 /Al2O3 the layers exhibit large changes in layer quality with thickness of the layers, ultimately affecting the magnetic properties of the stack.

The use of protective layers is of large importance when performing ex-situ measurements. Most of the materials used were capped by Al2O3, effectively hindering both the reaction with oxygen and water. The penetration of hydrogen through different thicknesses of alumina was investigated. The experiments confirmed high degree of passivation as well as the possibility to selectively diffuse hydrogen through these layers. The use of element specific diffusion barriers allows the tailoring of magnetic properties of magnetic thin films and multilayers.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2009. 69 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 665
Keyword
Multilayers, magnetic anysotropy, amorphous materials
National Category
Condensed Matter Physics
Research subject
Physics of Matter
Identifiers
urn:nbn:se:uu:diva-107425 (URN)978-91-554-7584-0 (ISBN)
Public defence
2009-09-24, Polhemssalen, Ångströmlaboratoriet, Ångströmlaboratoriet Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2009-09-02 Created: 2009-08-11 Last updated: 2010-12-16Bibliographically approved
2. Amorphous, Nanocrystalline, Single Crystalline: Morphology of Magnetic Thin Films and Multilayers
Open this publication in new window or tab >>Amorphous, Nanocrystalline, Single Crystalline: Morphology of Magnetic Thin Films and Multilayers
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Properties of magnetic thin film devices cannot be understood without detailed knowledge of their structure. For this purpose, a variety of thin film and multilayer systems have been studied. Both reciprocal space (low energy electron diffraction, reflection high energy electron diffraction, X-ray diffraction and reflectometry) and direct space (transmission electron microscopy) as well as Rutherford backscattering spectrometry have been applied.

To gain understanding of an oxidation procedure for the growth of magnetite layers, thermal stability of iron layers on molybdenum seed layers has been investigated.

Following the mosaicity and the out-of-plane coherence length over different ratios between the constituting layers allowed a deeper understanding of the limits of metallic superlattices. This, together with an approach to use hydrogen in the process gas during magnetron sputter epitaxy, opens routes for the growth of metallic superlattices of superior quality.

A non-isostructural multilayer/superlattice system, Fe/MgO, has been investigated. In turn, this gave more understanding how superlattice diffraction patterns are suppressed by strain fields.

As an alternative route to single-crystalline superlattices, amorphous multilayers present interesting opportunities. In this context, crystallization effects of iron/zirconium layers on alumiunium oxide were studied. Understanding these effects enables significant improvement in the quality of amorphous multilayers, and allows avoiding these, growing truly amorphous layers.

Both the substantial improvement in quality of metallic superlattices, approaching true single-crystallinity, as well as the improvements in the growth of amorphous multilayers give rise to opportunities in the field of magnetic coupling and superconducting spin valves.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 77 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 378
Keyword
Physics, Multilayer, Superlattice, X-ray diffraction, X-ray reflectometry, electron diffraction, Rutherford backscattering spectrometry, Interdiffusion, thin film growth, transmission electron microscopy, Epitaxial growth, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-8355 (URN)978-91-554-7055-5 (ISBN)
Public defence
2008-01-18, Polhemssalen, Ångströmlaboratoriet, Lagerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2010-03-09Bibliographically approved
3. Transmission Electron Microscopy for Characterization of Structures, Interfaces and Magnetic Moments in Magnetic Thin Films and Multilayers
Open this publication in new window or tab >>Transmission Electron Microscopy for Characterization of Structures, Interfaces and Magnetic Moments in Magnetic Thin Films and Multilayers
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Structural characterization is essential for the understanding of the magnetic properties of thin films and multilayers. In this thesis, both crystalline and amorphous thin films and multilayers were analyzed utilizing transmission electron microscopy (TEM). High resolution TEM and electron diffraction studies emphasize on the growth of amorphous Fe91Zr9 and Co68Fe24Zr8 on both Al2O3 and Al70Zr30 in multilayer structures by magnetron sputtering. The properties of the growth surfaces were found to strongly influence the formation of nano-crystallites of the magnetic material at interfaces. Field induced uniaxial magnetic anisotropy was found to be possible to imprint into both fully amorphous and partially crystallized Co68Fe24Zr8 layers, yielding similar magnetic characteristics regardless of the structure. These findings are important for the understanding of both growth and magnetic properties of these amorphous thin films.

As magnetic systems become smaller, new analysis techniques need to be developed. One such important step was the realization of electron energy-loss magnetic circular dichroism (EMCD) in the TEM, where information about the ratio of the orbital to spin magnetic moment (mL/mS) of a sample can be obtained. EMCD makes use of angular dependent inelastic scattering, which is characterized using electron energy-loss spectroscopy. The work of this thesis contributes to the development of EMCD by performing quantitative measurements of the mL/mS ratio. Especially, methods for obtaining energy filtered diffraction patterns in the TEM together with analysis tools of the data were developed. It was found that plural inelastic scattering events modify the determination of the mL/mS ratio, wherefore a procedure to compensate for it was derived. Additionally, utilizing special settings of the electron gun it was shown that EMCD measurements becomes feasible on the nanometer level through real space maps of the EMCD signal.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 86 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 669
Keyword
Transmission electron microscopy, TEM, magnetism, multilayer, superlattice, thin films, amorphous metals, electron energy-loss magnetic circular dichroism, EMCD, electron diffraction
National Category
Condensed Matter Physics Condensed Matter Physics Physical Sciences
Research subject
Engineering Science with specialization in Solid State Physics; Physics of Matter
Identifiers
urn:nbn:se:uu:diva-107941 (URN)978-91-554-7599-4 (ISBN)
Public defence
2009-10-16, Polhemsalen, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2009-09-24 Created: 2009-09-01 Last updated: 2011-05-02Bibliographically approved

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Raanaei, HosseinLidbaum, HansLiebig, AndreasLeifer, KlausHjörvarsson, Björgvin

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