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Gilbert damping of doped permalloy from first principles calculations
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0001-6509-5782
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The dynamic process of how fast a spintronic device can be switched from one state to another is characterized by the Gilbert damping parameter. It has been found that the Gilbert damping along with other intrinsic properties in permalloy, can be tuned by different dopants and doping concentration. Therefore, a study of intrinsic magnetic properties with emphasis on the dependence of the Gilbert damping parameter from first principles calculations is investigated. It is aimed at to give an insight of the microscopic understanding originated from electronic structure and to provide a guideline in the practical spintronic design. The topic of the present thesis is to investigate, by means of first principle calculations, how the variation of the Gilbert damping parameter depends upon the electronic structure of pure and doped permalloy. We show that the Gilbert damping has a monotonic increase with the doping concentration due to an increasing amount of scattering processes. The dopants of the 5d transition metal give rise to a much larger impact than the 4d, as the spin orbit coupling effect is more pronounced in the heavy elements. Our results are in satistying agreement with experiment.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , vi, 33 p.
Series
TRITA-ICT/MAP, 2015:02
Keyword [en]
Gilbert damping, DFT, Permalloy, SPR-KKR, Spin stiffness
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-170344ISBN: 978-91-7595-539-1 (print)OAI: oai:DiVA.org:kth-170344DiVA: diva2:827821
Presentation
2015-08-26, Sal C, KTH Electrum Isafjordsgatan22, Kista, 13:00 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note

QC 20150629

Available from: 2015-06-29 Created: 2015-06-29 Last updated: 2017-09-04Bibliographically approved
List of papers
1. Tunable permalloy-based films for magnonic devices
Open this publication in new window or tab >>Tunable permalloy-based films for magnonic devices
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2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 2, 024427Article in journal (Refereed) Published
Abstract [en]

Using both broadband ferromagnetic resonance (FMR) spectroscopy and ab initio calculations, we study the magnetodynamic properties of permalloy (Py, Ni80Fe20) and Py100-x M-x films with M as platinum (Pt), gold (Au), or silver (Ag). From the uniform FMR mode, we extract the saturation magnetization (M-S), damping (alpha), and inhomogeneous broadening (Delta H-0); from the first perpendicular standing spin-wave (PSSW) mode, we extract the exchange stiffness (A). M-S and A are found to decrease with increasing alloying, most strongly for Au and less so for Pt. On the other hand, alpha increases rapidly with both Pt and Au content, while being virtually independent of Ag content. The physical origins of the observed trends in alpha, M-S, and A are analyzed and explained using density functional theory calculations in the coherent potential approximation. The calculated trends quantitatively agree with the experimental observations. The drastically different impacts of Pt, Au, and Ag on the various fundamental magnetodynamic properties will allow for significant design freedom, where different properties can be varied independently of others through careful combinations of the Pt, Au, and Ag contents of Py100-x M-x films. By empirical approximations of each property's concentration dependence, we can dial in any desired combination of magnetodynamic properties within this parameter space. As a proof-of-principle demonstration we design a set of Py100-x-yPtxAgy films, where the saturation magnetization stays constant throughout the set and the damping can be tuned by a factor of 4.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-172712 (URN)10.1103/PhysRevB.92.024427 (DOI)000358600300006 ()2-s2.0-84938936223 (Scopus ID)
Funder
Swedish Research Council FormasKnut and Alice Wallenberg FoundationSwedish e‐Science Research Center
Note

Updated from "Manuscript" to "Article". QC 20150831

Available from: 2015-08-31 Created: 2015-08-27 Last updated: 2017-12-04Bibliographically approved

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