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Imprinting layer specific magnetic anisotropies in amorphous multilayers
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
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2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 2, 023918- p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate how layer specific in-plane magnetic anisotropy can be imprinted in amorphous multilayers. The anisotropy is obtained by growing the magnetic layers in the presence of an external field and the anisotropy direction can thereby be arbitrarily chosen for each of the magnetic layers. We used Co68Fe24Zr8 and Al70Zr30 layers as building blocks for demonstrating this effect. The imprinting is expected to be obtainable for a wide range of amorphous materials when grown at temperatures below the magnetic ordering temperature.

Place, publisher, year, edition, pages
AIP , 2009. Vol. 106, no 2, 023918- p.
Keyword [en]
Amourphous multilayers
National Category
Physical Sciences Engineering and Technology
Research subject
Physics of Matter
Identifiers
URN: urn:nbn:se:uu:diva-107510DOI: 10.1063/1.3169523ISI: 000268613000101OAI: oai:DiVA.org:uu-107510DiVA: diva2:231521
Available from: 2009-08-13 Created: 2009-08-13 Last updated: 2016-04-14Bibliographically 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. 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
3. Uncovering Magnetic Order in Nanostructured Disordered Materials: A Study of Amorphous Magnetic Layered Structures
Open this publication in new window or tab >>Uncovering Magnetic Order in Nanostructured Disordered Materials: A Study of Amorphous Magnetic Layered Structures
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The scope of this thesis is the study of the interplay between structure and magnetism in amorphous materials. The investigations focus on the growth of amorphous layers and the study of the influence of structural disorder and reduced physical extension on the magnetic properties of thin films and multilayers. The examined magnetic materials are FeZr alloys, as well as other amorphous transition metal alloys such as CoZr and FeCoZr.

Thin films and multilayers of the studied materials were deposited using magnetron sputtering in ultra-high vacuum conditions. Their amorphous structure and layering quality was investigated using X-ray scattering techniques and in several cases with transmission electron microscopy. The chemical composition of the alloys was determined with Rutherford Backscattering Spectrometry. The magnetic properties were investigated using the magneto-optic Kerr effect and SQUID magnetometry, as well as polarized neutron reflectometry and X-ray magnetic circular dicroism measurements.

For FeZr alloys deposited as multilayers with Al2O3 as spacer layer, it was found that Fe-rich nanocrystallites, formed at the metal/oxide interfaces, exert large influence on the magnetic properties. The use of AlZr alloys as buffer layers promotes the growth of highly amorphous FeZr layers. FeZr/AlZr multilayers with good layering quality can also be obtained. The influence of the reduced layer thickness on the magnetic moment, Curie temperature and magnetic dimensionality of the magnetic layers is addressed for FeZr/AlZr multilayers. Thin FeZr layers in these structures are found to belong to the 2D XY dimensionality class. The change of the magnetic moment and Curie temperature with reduced FeZr layer thickness is quantified.

In addition, the induced magnetic moment in the alloy element Zr was investigated in FeZr and CoZr alloy films. The possibility to imprint a preferred magnetization direction during thin film preparation was demonstrated for FeCoZr layers. Lastly, AlZr alloy films were studied with respect to their oxidation stability at room and elevated temperatures, aiming towards development of materials with passivating properties.

Place, publisher, year, edition, pages
Uppsala: Uppsala Universitet, 2011. 124 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 865
Keyword
Amorphous Materials, Magnetism, Amorphous Magnetism, Magnetic Measurements, Thin Films, Multilayers, Thin Film Deposition, Sputtering, FeZr Alloys, AlZr Alloys, X-ray Diffraction, Rutherford Backscattering Spectrometry
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-159913 (URN)978-91-554-8181-0 (ISBN)
Public defence
2011-11-24, Polhelmsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Supervisors
Available from: 2011-11-03 Created: 2011-10-11 Last updated: 2012-02-23Bibliographically approved

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Nguyen, HugoAndersson, GabriellaLidbaum, HansKorelis, PanagiotisLeifer, KlausHjörvarsson, Björgvin

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