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Interaction modiers in articial spin ices
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.ORCID iD: 0000-0001-5752-1980
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.ORCID iD: 0000-0002-1527-8668
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Department of Physics, Science Institute, University of Iceland.
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics Nano Technology
Identifiers
URN: urn:nbn:se:uu:diva-328864OAI: oai:DiVA.org:uu-328864DiVA, id: diva2:1148135
Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2018-01-12
In thesis
1. Tailoring the magnetic order in mesoscopic spin systems
Open this publication in new window or tab >>Tailoring the magnetic order in mesoscopic spin systems
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mesoscopic spin systems can be designed and fabricated using modern nano-fabrication techniques. These systems can contain large numbers of patterned ferromagnetic elements, for which the shape will generally determine their effective mesospin dimensionality. The lateral arrangement of these mesospins can be further used to tune the interactions between them.

With an appropriate choice of material, it is possible to define a temperature range where thermal fluctuations of these mesospins are experimentally accessible. To actively define this range, we use δ-doped Palladium, a three-layer system of Palladium—Iron—Palladium, for which the Curie-temperature scales with the Iron layer thickness. The patterned mesoscopic elements used in this work have a stadium-like shape that promotes a single magnetic domain state, thus making these islands behave as one-dimensional Ising-like mesospins that can be observed using magnetic imaging techniques.

We investigate the impact on the magnetic order resulting from modifications of the square spin ice geometry. By adding, removing and merging elements in the square artificial spin ice architecture, energy-landscape variations can be realized. Firstly, an added interaction modifier is used to equilibrate the interactions between the mesospins at the vertex level, which can restore the degenerate ground state of the square spin ice model. Secondly, the removal of elements can lead to topologically frustrated spin systems, as not all building blocks can simultaneously be in their lowest energy state. Furthermore, the merging results in multiple element sizes in the mesospin system. As the magnetization reversal barrier is dependent on the element size, these mesospin systems have different energy barriers. The thermal ordering process in such a system differs from a single-size element system with its unique energy barrier. Using reciprocal space analysis tools like the magnetic spin structure factor we show that systems with multiple element sizes achieve a higher short-range order then their single-size element references. The magnetic order in mesoscopic spin systems could successfully be tailored by modifications of the lattice geometry.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 78
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1574
Keyword
artificial spin ice, magnetic nano-structures, mesoscopic spin systems, mesospins, model systems, Shakti, Saint George, interaction modifier, engineering of energy-landscape, multiple energy-scales
National Category
Condensed Matter Physics Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-328790 (URN)978-91-513-0099-3 (ISBN)
Public defence
2017-11-28, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2017-11-03 Created: 2017-10-10 Last updated: 2017-11-03
2. Collective properties of magnetic mesospins
Open this publication in new window or tab >>Collective properties of magnetic mesospins
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mesoscopic spin systems consist of an ensemble of lithographically patterned nanomagnetic elements - mesospins. The interactions between the mesospins, can be designed at will by altering their lateral arrangement, enabling the study of collective magnetic order in a wide range of systems.          

  The spin dimensionality of a mesospin is controlled by its shape and form. Thin elongated elements are Ising-like, with only two possible magnetization directions. Disc shaped elements can be single domain and behave XY-like, with a magnetization direction free to rotate in the plane of the disc. Larger disc sizes result in magnetic vortices. Tuning the material parameters of the elements enables mesospin dynamics at and below room temperature. Combining all of the above, the magnetic state of a lattice is then defined by the mesospins lateral arrangement, their spin dimensionality, and the temperature.          

  In this Thesis we investigate the magnetic order and dynamic properties in a series of different configurations, where the nano-magnetic elements are in the vortex state, Ising-like mesospins or of mixed mesospin dimensionality. Chains of Ising-mesospins were investigated and shown to be successfully described by the Ising model. A lossless transition between the magnetic vortex state and the collinear state, was found in square arrays of magnetic discs. In a more complicated interaction regime, square artificial spin ice, the dynamical range of the Ising-like mesospins in the lattice was probed, in terms of magnetization relaxation studies.          

  Utilizing the configurational freedom in mesoscopic spin systems, together with the possibility to alter the spin dimensionality of the elements, it is possible to create a lattice with no naturally occurring analogue. In such a lattice, where XY mesospins were added to square artificial spin ice, it was found that the degeneracy of the square ice model was restored. Furthermore, using a reciprocal space analysis tool, the magnetic spin structure factor, the system was shown to possess the characteristic features of a Coulomb spin liquid with strong local correlations and absence of long range order. Increasing the interaction between the elements, results in an emergent magnetic order on a large length-scale.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 89
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1619
Keyword
artificial spin ice, magnetic nano-structures, mesoscopic spin systems, mesospins, mixed spin dimensionalities, interaction modifier, engineering of energy landscape, emergence
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-338722 (URN)978-91-513-0205-8 (ISBN)
Public defence
2018-03-02, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2018-02-06 Created: 2018-01-12 Last updated: 2018-03-08

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