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Magnetic Order in Artificial Structures
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The topic of this thesis is the investigation of the magnetic properties of artificially created magnetic structures. Applying different characterization techniques, ranging from direct imaging methods to reciprocal space techniques, the properties of lithographically patterned arrays of magnetic thin film and multilayer elements are investigated by exploring their magnetic state, extending from the atomic scale up to collective ordering phenomena of nano-magnetic elements.

Laterally patterned amorphous multilayer arrays of combined circular and ellipsoidal islands were investigated. The arrays contain a variety of length scales, ranging from their nanometer scale multilayer structure to their lateral periodicity in the micrometer range. The attributes of these arrays are explored using different techniques, applicable for addressing the magnetization at different length scales, including magneto-optical techniques, micromagnetic simulations and x-ray resonant magnetic scattering.

Arrays of dipole interacting elongated magnetic elements composed of Pd(Fe) thin films were investigated. Pd(Fe) films have a low Curie temperature which can be tuned by the thickness of the Fe layer embedded in Pd. By this, the interaction and the shape anisotropy energies can be brought down to energy scales comparable to room temperature enabling the possibility of investigating the effect of thermal excitations on such arrays. The temperature dependent magnetization of an artificial square spin ice array was investigated by magneto-optical measurements demonstrating the possibility of observing an order-disorder transition in an artificial square spin ice system. The role of dipolar interactions and the possibility of achieving thermal ground state ordering was then further investigated by magnetically sensitive photoemission electron microscopy imaging of ring arrangements of elongated Pd(Fe) elements. The results reveal a high probability of achieving a thermal ground state ordering of the magnetization of the islands.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 922
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-172386ISBN: 978-91-554-8339-5 (print)OAI: oai:DiVA.org:uu-172386DiVA: diva2:514505
Public defence
2012-05-24, Häggsalen, Ångströmlaboratoriet, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2012-05-03 Created: 2012-04-10 Last updated: 2012-08-01Bibliographically approved
List of papers
1. Magnetic structure and diffracted magneto-optics of patterned amorphous multilayers
Open this publication in new window or tab >>Magnetic structure and diffracted magneto-optics of patterned amorphous multilayers
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 14, 144434-1-144434-8 p., 144434Article in journal (Refereed) Published
Abstract [en]

We present magneto-optical Kerr effect measurements of patterned arrays of Co68Fe24Zr8 / Al2O3 amorphous multilayers. The multilayers were patterned in two dimensions into two different arrangements of circular and ellipsoidal islands. Magnetization loops were recorded in a longitudinal geometry using both the specularly reflected beam as well as diffracted beams scattered off the patterned films. The magnetization of the patterned structures is significantly different from the magnetization of a continuous multilayer owing to the lateral confinement of the pattern and the introduction of additional dipolar coupling between the layers at the edges of the islands. By investigating the magnetic response at the different diffraction orders from the two different configurations of islands we are able to observe the magnetization at different length scales and determine the magnetic response of the circular and ellipsoidal islands individually.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-133717 (URN)10.1103/PhysRevB.82.144434 (DOI)000283423000004 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2010-11-18 Created: 2010-11-15 Last updated: 2017-12-12Bibliographically approved
2. X-ray resonant magnetic scattering from patterned multilayers
Open this publication in new window or tab >>X-ray resonant magnetic scattering from patterned multilayers
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2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 6, 064426- p.Article in journal (Refereed) Published
Abstract [en]

We report on x-ray resonant magnetic scattering from laterally patterned arrays of amorphous Co68Fe24Zr8/Al2O3 multilayers. The arrays are composed of circular and ellipsoidal elements which display distinct individual magnetic responses enabling the investigation of the dependence of the observed magnetization on the scattering condition. We focus our attention to special points in reciprocal space, relating to the lateral and perpendicular structure of the samples, thereby revealing the magnetic structure of the multilayered arrays. This allows a comparison of the observed magnetization under different scattering conditions to magneto-optical measurements. The scattering data are supported by micromagnetic simulations which further enhance our understanding of the intricate charge and magnetic scattering from three dimensional patterns.

National Category
Atom and Molecular Physics and Optics
Research subject
Physics of Matter
Identifiers
urn:nbn:se:uu:diva-172373 (URN)10.1103/PhysRevB.86.064426 (DOI)000307719400003 ()
Available from: 2012-04-09 Created: 2012-04-09 Last updated: 2017-12-07Bibliographically approved
3. Melting artificial spin ice
Open this publication in new window or tab >>Melting artificial spin ice
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2012 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 14, 035009- p.Article in journal (Refereed) Published
Abstract [en]

Artificial spin ice arrays of micromagnetic islands are a means of engineering additional energy scales and frustration into magnetic materials. Here we demonstrate a magnetic phase transition in an artificial square spin ice and use the symmetry of the lattice to verify the presence of excitations far below the ordering temperature. We do this by measuring the temperature dependent magnetisation in different principal directions and comparing with simulations of idealised statistical mechanical models. Our results confirm a dynamical pre-melting of the artificial spin ice structure at a temperature well below the intrinsic ordering temperature of the island material. We thus create a spin ice array that has real thermal dynamics of the artificial spins over an extended temperature range.

Keyword
artificial spin ice, ising model, magnetization dynamics
National Category
Other Physics Topics
Research subject
Physics of Matter
Identifiers
urn:nbn:se:uu:diva-168982 (URN)10.1088/1367-2630/14/3/035009 (DOI)000302342000002 ()
Funder
Swedish Research Council
Available from: 2012-02-21 Created: 2012-02-21 Last updated: 2017-12-07Bibliographically approved
4. Thermalized ground state of artificial kagome spin ice building blocks
Open this publication in new window or tab >>Thermalized ground state of artificial kagome spin ice building blocks
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2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 11, 112404- p.Article in journal, Letter (Other academic) Published
Abstract [en]

We present a direct magnetic imaging study on the thermal macrospin ordering of artificial kagome spin ice building blocks. Using photoemission electron microscopy, employing x-ray magnetic circular dichroism, we are able to resolve the single domain magnetic nature of the macrospins and determine the states of the combined building block structures. The nano-patterning and material selection allows thermally activated magnetization reversal for the macrospins to occur. The ordering of the macrospins is dominated by the ground state, consistent with a thermal ground state ordering. This work paves the way for the realization of extended artificial spin ice structures exhibiting experimentally accessible thermal behavior

National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-172374 (URN)10.1063/1.4751844 (DOI)000309329300045 ()
Available from: 2012-04-09 Created: 2012-04-09 Last updated: 2017-12-07Bibliographically approved
5. Element specific magnetization in Fe/Pd quantum well structures
Open this publication in new window or tab >>Element specific magnetization in Fe/Pd quantum well structures
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-168443 (URN)
Available from: 2012-02-16 Created: 2012-02-10 Last updated: 2012-08-01

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