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Oscillatory exchange coupling in the two-dimensional limit
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
2005 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, L477-483 p.Article in journal (Refereed) Published
Abstract [en]

The dimensionality aspects of the order–disorder transition in single and double magnetic layers is addressed. A single Fe film of three monolayers, embedded in V(001) layers, was determined to be two-dimensional and XY-like. Two Fe layers, separated by 14.4 monolayers of V(001), were determined to belong to the same universality class as the single Fe film. The interlayer exchange coupling was altered in situ by introducing hydrogen in the V layers. An oscillation of the ordering temperature was observed, consistent with an oscillatory interlayer exchange coupling. The two-dimensional nature of the bilayer was confirmed by the ratio of the interlayer and intralayer couplings (). The results therefore support the existence of an oscillatory exchange coupling in the quasi-two-dimensional limit.

Place, publisher, year, edition, pages
2005. Vol. 17, L477-483 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95878DOI: 10.1088/0953-8984/17/44/L03OAI: oai:DiVA.org:uu-95878DiVA: diva2:170247
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2012-03-07Bibliographically approved
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. 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

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