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The influence of interlayer exchange coupling on the magnetic ordering 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.
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2009 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 321, no 9, 1214-1220 p.Article in journal (Refereed) Published
Abstract [en]

The relation between the interlayer exchange coupling and magnetic order is addressed, using Fe/V(0 0 1) superlattices as a model system. Large decrease in the ordering temperature (Tc) is observed with decreasing interlayer exchange coupling. The effective exponents of the magnetization were determined to be larger than 0.5 for all the samples, which is strongly deviating from the classical values of both two- and three-dimensional systems. This effect can partially be ascribed to the presence of boundaries, invoked by the finite number of magnetic layers.

Place, publisher, year, edition, pages
2009. Vol. 321, no 9, 1214-1220 p.
Keyword [en]
Magnetic superlattices, Magnetic phase transitions, Critical exponents
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96975DOI: 10.1016/j.jmmm.2008.11.010ISI: 000264170500022OAI: oai:DiVA.org:uu-96975DiVA: diva2:171729
Available from: 2008-04-02 Created: 2008-04-02 Last updated: 2013-09-26Bibliographically approved
In thesis
1. Magnetic Ordering in Layered Magnets
Open this publication in new window or tab >>Magnetic Ordering in Layered Magnets
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The preparation of layered magnets needs the knowledge of growth techniques which are focused on the growth of Fe/V(001) superlattices. Such films have been structurally investigated by X-rays reflectivity and diffraction.

The magnetic investigations have been carried out by magneto-optic Kerr effect (MOKE), Superconducting Quantum Interference Device (SQUID) magnetometry and polarized neutron reflectivity (PNR). This latter technique has been used in cooperation with the Institute Laue Langvin (Grenoble, France) and Ruhr Universität (Bochum, Germany).

The cross-over in universality class is shown in a series of layered magnets where a δ-doping layer of Fe has been embedded between two layers of Pd showing that the magnetization depends on the effective magnetic thickness of the polarized Pd. A model for the cross-over has been developed in terms of magnetic excitations.

The interlayer exchange coupling (IEC) mediated by a non-magnetic spacer has been reviewed focusing the attention on the recent theoretical and experimental works based on Fe/V(001) superlattices.

The IEC can be tailored at will by reversibly alloying of the spacer with H: this has been proved in Fe/V(001) double layers showing that in the two dimensional limit, the universality class is not affected by the coupling.

The magnetic order-disorder transitions in Fe/V(001) superlattices do not seem to belong to any universality class. A phenomenological model which accounts for the effective coupling at the boundaries has been developed.

The influence of the inherent ordering temperatures of single magnetic layers has been investigated in Fe/V(001) superlattices proving that the weakest ferromagnetic layer affects the overall magnetic ordering.

A new kind of layered magnet has been developed to increase the effect of the boundaries. PNR measurements show that the universality class depends on which length-scale is investigated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 88 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 418
Keyword
Physics, Magnetic thin films and superlattices, Magnetic phase transitions, Polarized neutron reflectometry, Fysik
Identifiers
urn:nbn:se:uu:diva-8604 (URN)978-91-554-7147-7 (ISBN)
Public defence
2008-04-24, Polhemssalen, Ångströmlaboratoriet, Lagerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2008-04-02 Created: 2008-04-02 Last updated: 2010-03-08Bibliographically approved
2. 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

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