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Electronic Structure and Atomistic Spin Dynamics of Nanostructured Materials
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Faculdade de Física, Universidade Federal do Pará.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The theoretical studies of several magnetic materials are presented in this thesis. To each of them, it was investigated the electronic structure, by means of density functional theory calculations, and/or magnetization dynamics, in the context of atomistic spin dynamics (ASD).  For bulk properties, we evaluate the magnon spectra of the heavy rare earths (Gd, Tb, Dy, Ho, Er, and Tm), using the exchange parameters and magnetic moments from first-principles calculations in ASD simulations. Additionally, we performed Monte Carlo simulations that nicely reproduced the qualitative trend of lowering of the critical temperatures across the series. Next, we discuss about the microscopic mechanism of the vanishingly low magnetic anisotropy of Permalloy using the concept of the orbital moment anisotropy for Fe and Ni atoms in the alloy.  Turning to surface magnetism, we discuss the use of exchange parameters computed by a noncollinear formalism for 6 monolayers of Fe on the Ir(001) substrate, in order to have a more accurate description of magnons at finite temperature and to obtain good comparison with experimental data. Besides that, we also studied surface magnons on 3 and 9 Ni monolayers on Cu(001) and Cu(111) in order to track the significant surface and/or interface effects and contrast it to properties that are fcc Ni bulk-like. Likewise, we used the Monte Carlo method to estimate the critical temperatures of Ni surfaces and compared with experimental data.  Finally, in the field of low dimensional magnetism, we present the ab-initio calculations for the electronic structure of Cr nanostructures of diverse geometries adsorbed on the Pd(111) surface, with focus on the formation of non-collinear spin configurations, either due to geometric frustration or the spin-orbit coupling provided by the substrate.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , 39 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1510
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-319994ISBN: 978-91-554-9903-7 (print)OAI: oai:DiVA.org:uu-319994DiVA: diva2:1088309
Public defence
2017-06-02, Seminar room, Federal University of Pará, Av. Augusto Correa, 01., Belém, 13:15 (English)
Opponent
Supervisors
Available from: 2017-05-05 Created: 2017-04-12 Last updated: 2017-06-27Bibliographically approved
List of papers
1. The standard model of the rare-earths, analyzed from the Hubbard-Iapproximation
Open this publication in new window or tab >>The standard model of the rare-earths, analyzed from the Hubbard-Iapproximation
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(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-267579 (URN)
Available from: 2015-11-24 Created: 2015-11-24 Last updated: 2017-04-12
2. Magnetic anisotropy in Permalloy: hidden quantum mechanical features
Open this publication in new window or tab >>Magnetic anisotropy in Permalloy: hidden quantum mechanical features
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(English)Manuscript (preprint) (Other academic)
Keyword
Permalloy, Orbital Anisotropy, Anisotropy Energy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-319925 (URN)
Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2017-04-12
3. Finite-temperature interatomic exchange and magnon softening in Fe overlayers on Ir(001)
Open this publication in new window or tab >>Finite-temperature interatomic exchange and magnon softening in Fe overlayers on Ir(001)
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2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 1, 014413Article in journal (Refereed) Published
Abstract [en]

We evaluate how thermal effects soften the magnon dispersion in 6 layers of Fe(001) on top of Ir(001). We perform a systematic study considering noncollinear spin arrangement and calculate configuration-dependent exchange parameters J(ij)(nc) following the methodology described by Szilva et al. [Phys. Rev. Lett. 111, 127204 (2013)]. In addition, Monte Carlo simulations were performed in order to estimate the noncollinear spin arrangement as a function of temperature. Hence the J(ij)(nc)'s related to these configurations were calculated and used in an atomistic spin dynamics approach to evaluate the magnon spectra. Our results show good agreement with recent room-temperature measurements, and highlights how thermal effects produce magnon softening in this, and similar, systems.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-300459 (URN)10.1103/PhysRevB.94.014413 (DOI)000379497400007 ()
Funder
Swedish Research Council, 2013.0020; 2012.0031
Available from: 2016-08-09 Created: 2016-08-09 Last updated: 2017-04-12Bibliographically approved
4. Surface magnons and critical temperatures of Ni surfaces on Cu
Open this publication in new window or tab >>Surface magnons and critical temperatures of Ni surfaces on Cu
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-319991 (URN)
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-04-12
5. First-principles theory of electronic structure and magnetism of Cr nano-islands on Pd(111)
Open this publication in new window or tab >>First-principles theory of electronic structure and magnetism of Cr nano-islands on Pd(111)
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2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 2, 025807Article in journal (Refereed) Published
Abstract [en]

We report on the electronic structure, magnetic moments and exchange interactions of one-and two-dimensional Cr clusters on a Pd(1 1 1) substrate, using a real-space method based on density functional theory in the local spin density approximation. We find in general that for the investigated clusters, the magnetic moments are sizeable and almost entirely of spin-character. We demonstrate that the interactions in general are dominated by nearest-neighbor antiferromagnetic Heisenberg form, which implies that Cr on Pd(1 1 1) forms an ideal model system, in which clusters of almost any shape and size can be investigated from a Heisenberg Hamiltonian, using a nearest-neighbor exchange model. We have also found that complex magnetic structures can be realized for linear chains of Cr, due to a competition between exchange interaction and a weaker Dzyaloshinskii-Moriya interaction.

Keyword
nanomagnetism, electronic structure, metallic nanowires
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-311166 (URN)10.1088/0953-8984/29/2/025807 (DOI)000388615900007 ()
Funder
Knut and Alice Wallenberg Foundation, 2013.0020 2012.0031Swedish Research Council
Available from: 2016-12-22 Created: 2016-12-22 Last updated: 2017-04-12Bibliographically approved

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