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Finite temperature properties of transition metal alloys using extended spin model
KTH, School of Engineering Sciences (SCI). KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-6509-5782
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-213369OAI: oai:DiVA.org:kth-213369DiVA, id: diva2:1136983
Funder
Swedish Research Council, 2015-04608Swedish Research Council, 2016-05980Swedish Energy Agency, P40147-1
Note

QC 20170904

Available from: 2017-08-29 Created: 2017-08-29 Last updated: 2017-09-04Bibliographically approved
In thesis
1. A theoretical study of magnetism and its extension to finite temperatures in random alloys
Open this publication in new window or tab >>A theoretical study of magnetism and its extension to finite temperatures in random alloys
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work presents new theoretical developments of atomistic spin simulations of magnetic materials at finite temperatures. Special focus is put on the description of longitudinal magnetic fluctuations and the application in random transition metal alloys. A new computational scheme is proposed for mapping total energies from electronic structure calculations to an extended atomistic spin model. The proposed model has some new appealing features from previous models. To be more specific, the proposed model successfully eliminates the reference state dependency of the mapping that previous models have suffered from. Moreover, the proposed model includes longitudinal magnetic fluctuations that gives an improved description of the magnetic properties over a larger temperature interval. The proposed model strives to find the right compromise between accuracy and computational feasibility and it is applied not only to the elemental systems Fe, Co and Ni, but also to a number of binary transition metal alloys such as Permalloy (Fe$_{20\%}$Ni$_{80\%}$) and Fe-Co systems.

Electronic structure calculations of Gilbert damping and the closely related magnetodynamic properties, the saturation magnetization and exchange stiffness, have been conducted for a number of different magnetic systems including Permalloy with additional doping of $4d$ or $5d$ transition metal impurities and the full Heusler alloy Co$_2$FeAl. Regarding the Permalloy based systems, a systematic study of the magnetodynamic properties was performed and compared with existing experimental data. In general we found good agreement and manage to explain the main trends regarding the Gilbert damping across the series with a simple model that captures the most important material properties to the damping, namely the spin orbit coupling and density of states at the Fermi level. In Co$_2$FeAl, we calculated the Gilbert damping in different existing crystal structures and compare those with new experimental data and found good agreement between them.

Magnon properties of random alloys, like Permalloy, are studied using two complementory methods, the adiabatic magnon spectra valid at zero temperature and from finite temperature atomistic spin dynamics through the dynamical structure factor. The influence of chemical disorder and temperature effects on the magnon properties are investigated that hopefully could motivate new experimental studies of these materials.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. p. 82
Series
TRITA-FYS, ISSN 0280-316X
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-213460 (URN)978-91-7729-502-0 (ISBN)
Public defence
2017-09-29, Sal B, Electrum 229, Kistagången 16, Kista, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2015-04608Swedish Research Council, 2016-05980Swedish Energy Agency, P40147-1
Note

QC 20170904

Available from: 2017-09-04 Created: 2017-08-31 Last updated: 2017-09-04Bibliographically approved

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Pan, FanBergqvist, Lars

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