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The effect of strain and interfaces on the orbital moment in Fe/V superlattices
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2007 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 313, no 1, 230-235 p.Article in journal (Refereed) Published
Abstract [en]

The dependence of the Fe orbital moment on strain and interfaces in Fe/V superlattices has been investigated by X-ray magnetic circular dichroism (XMCD). The orbital moment was determined to be lower at the interfaces than in the bulk, which we attribute to Fe–V hybridization. An enhancement of the orbital moment with increasing strain in the Fe layers was observed. This enhancement is attributed to an unquenching of the orbital moment. Consequently, the orbital moment of Fe in Fe/V is concluded to be influenced by two competing parameters. It is lowered by increasing interface density, and enhanced by increasing strain.

Place, publisher, year, edition, pages
2007. Vol. 313, no 1, 230-235 p.
Keyword [en]
Superlattice, Orbital moment, Strain, Interfaces, X-ray magnetic circular dichroism
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95879DOI: 10.1016/j.jmmm.2007.01.003ISI: 000246130000037OAI: oai:DiVA.org:uu-95879DiVA: diva2:170248
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2017-12-14
In thesis
1. The Influence of Interlayer Exchange Coupling on Magnetic Ordering in Fe-based Heterostructures
Open this publication in new window or tab >>The Influence of Interlayer Exchange Coupling on Magnetic Ordering in Fe-based Heterostructures
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Temperature dependent magnetization measurements were conducted on Fe-based heterostructures. A linear increase of the magnetic critical temperature with increasing Fe thickness was found for Fe/V superlattices with strong interlayer exchange coupling. For weakly coupled Fe/V superlattices anomalous values of the critical exponent β were attributed to differences in the effective interlayer exchange coupling in the surface region and in the interior of the superlattice stack.

Hydrogen loading of a sample containing a thin Fe film, up to a maximum pressure of 4 mbar gave an increase of the magnetic critical temperature of ≈21 K. A sample with a double layer of Fe, exchange coupled over V, showed oscillations in the critical temperature when loaded to increasing pressure of hydrogen. The oscillations in the critical temperature indicate the presence of quasi-2D phases.

Superlattices of Fe and V were investigated by x-ray magnetic circular dichroism. It was found that the orbital magnetic moment shows the same trend as the magnetic anisotropy energy with thickness of the Fe layers. A model which takes into account a varying strain and interface density successfully described the changes in the orbital magnetic moment.

The magnetization was measured as a function of temperature for a series of magnetically δ-doped Pd samples. A thin film of Fe induced a magnetic moment in surrounding Pd layers, leading to a magnetic thickness one order of magnitude larger than the thickness of the Fe film. A crossover in the magnetic spatial dimensionality was found as the thickness of the Fe film increased from ≈0.4 monolayers to ≈1 monolayer. First principle calculations of the magnetization profile together with a spin wave quantum well model were used to explain the dimensionality crossover by an increase in the available thermal energy for population of perpendicular spin wave modes.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. viii, 66 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 307
Keyword
Physics, magnetism, magnetic dimensionality, MOKE, magneto-optics, hydrogen loading, phase transitions, Fysik
Identifiers
urn:nbn:se:uu:diva-7885 (URN)978-91-554-6890-3 (ISBN)
Public defence
2007-05-31, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2013-09-26Bibliographically approved
2. 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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 308
Keyword
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
Identifiers
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)
Opponent
Supervisors
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2011-11-17Bibliographically approved

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Björck, MattsAndersson, GabriellaHjörvarsson, Björgvin

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