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GenX: an extensible X-ray reflectivity refinement program utilizing differential evolution
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
2007 (English)In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 40, no 6, 1174-1178 p.Article in journal (Refereed) Published
Abstract [en]

GenX is a versatile program using the differential evolution algorithm for fitting X-ray and neutron reflectivity data. It utilizes the Parratt recursion formula for simulating specular reflectivity. The program is easily extensible, allowing users to incorporate their own models into the program. This can be useful for fitting data from other scattering experiments, or for any other minimization problem which has a large number of input parameters and/or contains many local minima, where the differential evolution algorithm is suitable. In addition, GenX manages to fit an arbitrary number of data sets simultaneously. The program is released under the GNU General Public License.

Place, publisher, year, edition, pages
2007. Vol. 40, no 6, 1174-1178 p.
Keyword [en]
X-ray reflectivity, neutron reflectivity, differential evolution algorithm, genetic algorithm
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-16430DOI: 10.1107/S0021889807045086ISI: 000250895200025OAI: oai:DiVA.org:uu-16430DiVA: diva2:44201
Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2011-11-17Bibliographically approved
In thesis
1. A Structural Viewpoint of Magnetism in Fe and Co Based Superlattices
Open this publication in new window or tab >>A Structural Viewpoint of Magnetism in Fe and Co Based Superlattices
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In order to understand the properties of thin film devices, knowledge of the material's structure is essential. The work presented here combines magnetic and structural characterization of the systems studied to gain a deeper physical understanding. The magnetic properties have been studied with a combination of x-ray magnetic circular dichroism, SQUID magnetometry and magneto-optical Kerr effect. For the structural characterization, x-ray reflectivity and diffraction have been used, complemented by neutron diffraction and transmission electron microscopy.

One structural property that affects the magnetic moment in metal-on-metal superlattices is interdiffusion between the layers. This is discussed for bcc Fe/Co(001) and bcc Fe81Ni19/Co(001) superlattices. The effect of interdiffusion was seen as a large region of enhanced magnetic moments as compared to theoretical calculations, which assume perfectly sharp interfaces. For the Fe81Ni19/Co(001) superlattices the chemical interface region, as revealed by neutron diffraction, was in good agreement with the region of magnetic enhancement.

Another structural property that has been investigated is the strain in the magnetic layers. This does not affect the spin magnetic moment to a large extent. However the magnetocrystalline anisotropy and the orbital moment are affected by the presence of strain. The effects on the orbital moment from strain and interfaces for Fe in Fe/V superlattices was studied, and it was found that the two contributions were separable.

In this context the effect of strain on the out-of-plane magnetocrystalline anisotropy in FeCo/Pt has also been studied. The latter system is interesting from a technological perspective since tetragonally distorted FeCo alloys have the potential to be suitable new materials in computer hard drives.

Finally, a computer program, based on the Differential Evolution algorithm, to refine primarily x-ray reflectivity data, is presented.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 92 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 308
Physics, Magnetism, Multilayer, Superlattice, X-ray magnetic circular dichroism, X-ray diffraction, X-ray reflectivity, Neutron diffraction, Structural refinement, Interfaces, Fysik
National Category
Natural Sciences
urn:nbn:se:uu:diva-7886 (URN)978-91-554-6891-0 (ISBN)
Public defence
2007-06-01, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2011-11-17Bibliographically approved

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Björck, MattsAndersson, Gabriella
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