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Tailoring the magnetic order in mesoscopic spin systems
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.ORCID iD: 0000-0002-1527-8668
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
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
Keywords [en]
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: urn:nbn:se:uu:diva-328790ISBN: 978-91-513-0099-3 (print)OAI: oai:DiVA.org:uu-328790DiVA, id: diva2:1148141
Public defence
2017-11-28, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilAvailable from: 2017-11-03 Created: 2017-10-10 Last updated: 2017-11-03
List of papers
1. A new look on the two-dimensional Ising model: thermal artificial spins
Open this publication in new window or tab >>A new look on the two-dimensional Ising model: thermal artificial spins
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2016 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 18, article id 023008Article in journal (Refereed) Published
Abstract [en]

We present a direct experimental investigation of the thermal ordering in an artificial analogue of an asymmetric two-dimensional Ising system composed of a rectangular array of nano-fabricated magnetostatically interacting islands. During fabrication and below a critical thickness of the magnetic material the islands are thermally fluctuating and thus the system is able to explore its phase space. Above the critical thickness the islands freeze-in resulting in an arrested thermalized state for the array. Determining the magnetic state we demonstrate a genuine artificial two-dimensional Ising system which can be analyzed in the context of nearest neighbor interactions.

Keywords
magnetic ordering, artificial spins, Ising model
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-288634 (URN)10.1088/1367-2630/18/2/023008 (DOI)000372453700002 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2016-05-04 Created: 2016-04-28 Last updated: 2017-11-30Bibliographically approved
2. Thermally induced magnetic relaxation in square artificial spin ice
Open this publication in new window or tab >>Thermally induced magnetic relaxation in square artificial spin ice
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2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 37097Article in journal (Refereed) Published
Abstract [en]

The properties of natural and artificial assemblies of interacting elements, ranging from Quarks to Galaxies, are at the heart of Physics. The collective response and dynamics of such assemblies are dictated by the intrinsic dynamical properties of the building blocks, the nature of their interactions and topological constraints. Here we report on the relaxation dynamics of the magnetization of artificial assemblies of mesoscopic spins. In our model nano-magnetic system - square artificial spin ice - we are able to control the geometrical arrangement and interaction strength between the magnetically interacting building blocks by means of nano-lithography. Using time resolved magnetometry we show that the relaxation process can be described using the Kohlrausch law and that the extracted temperature dependent relaxation times of the assemblies follow the Vogel-Fulcher law. The results provide insight into the relaxation dynamics of mesoscopic nano-magnetic model systems, with adjustable energy and time scales, and demonstrates that these can serve as an ideal playground for the studies of collective dynamics and relaxations.

National Category
Physical Sciences Materials Engineering
Identifiers
urn:nbn:se:uu:diva-315927 (URN)10.1038/srep37097 (DOI)000392061500001 ()27883013 (PubMedID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2017-02-22 Created: 2017-02-22 Last updated: 2018-01-12Bibliographically approved
3. Interaction modiers in articial spin ices
Open this publication in new window or tab >>Interaction modiers in articial spin ices
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics Nano Technology
Identifiers
urn:nbn:se:uu:diva-328864 (URN)
Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2018-01-12
4. Magnetic order and energy-scale hierarchy in articial spin ice
Open this publication in new window or tab >>Magnetic order and energy-scale hierarchy in articial spin ice
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(English)Manuscript (preprint) (Other academic)
Keywords
artificial spin ice, magnetic nano-structures, mesoscopic spin systems, mesospins, model systems, Shakti, engineering of energy-landscape, multiple energy-scales
National Category
Condensed Matter Physics Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-329016 (URN)
Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2017-10-10

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