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Experimental realization of amorphous two-dimensional XY magnets
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 2, 024430- p.Article in journal (Refereed) Published
Abstract [en]

The temperature dependence of the magnetization of thin amorphous Fe(89)Zr(11)/Al(78)Zr(22) layerswas investigated. Dimensionality analysis of the ferromagnetic transition of 15 A thick layers yielded critical exponents characteristic of the 2D XY (planar rotor) model. Above the ordering temperature significant polarizability with an applied field is observed, due to the existence of large-scale magnetic correlations, of which the extent and origin have been determined.

Place, publisher, year, edition, pages
2011. Vol. 84, no 2, 024430- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-156953DOI: 10.1103/PhysRevB.84.024430ISI: 000292873700002OAI: oai:DiVA.org:uu-156953DiVA: diva2:435832
Available from: 2011-08-20 Created: 2011-08-11 Last updated: 2017-12-08Bibliographically approved
In thesis
1. 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
2. Critical Phenomena and Exchange Coupling in Magnetic Heterostructures
Open this publication in new window or tab >>Critical Phenomena and Exchange Coupling in Magnetic Heterostructures
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The continuous phase transition in thin magnetic films and superlattices has been studied using the magneto-optical Kerr effect (MOKE) and polarized neutron scattering (PNR).  It has been shown that the critical behavior of amorphous thin films belonging to the 2D XY universality class can be described within the same theory as crystalline sample. This means that quenched disorder only serves as a marginal perturbation in systems with this symmetry.

The connection between interlayer exchange coupling and the observed critical behavior in Fe/V superlattices was explored. The results prove that the origin of unusually high values of the exponent β can be traced to a position dependence of the magnetization at elevated temperatures. The magnetization of the outermost layers within the superlattice shows a more pronounced decrease at lower temperatures, compared to the inner layers, which in turn have a more abrupt decrease in the vicinity of the critical temperature. This translates to a high exponent, especially when the layers are probed by a technique where more weight is given to the layers close to the surface, e.g.MOKE.  The interlayer exchange coupling as a function of spacer thickness and temperature was also studied in its own right. The data was compared to the literature, and a dependence on the thickness of the magnetic layers was concluded.

The phase transition in amorphous FeZr/CoZr multilayers, where the magnetization emanates from ferromagnetic proximity effects, was investigated. Even though the determined exponents of the zero-field magnetization, the susceptibility and the critical isotherm did not correspond to any universality class, scaling plots displayed an excellent data collapse.

Samples consisting of Fe δ-layers (0.3-1.4 monolayers) embedded in Pd were studied using element-specific resonant x-ray magnetic scattering. The magnetization of the two constituents showed distinctly different temperature dependences.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 902
Keyword
phase transitions, critical behavior, 2D XY model, MOKE, magnetic thin films and superlattices, amorphous multilayers, magnetic proximity effects
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-168310 (URN)978-91-554-8282-4 (ISBN)
Public defence
2012-03-30, Å80101, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2012-03-09 Created: 2012-02-08 Last updated: 2012-03-29Bibliographically approved

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Korelis, Panagiotis T.Ahlberg, MartinaHjörvarsson, Björgvin

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