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Tunable permalloy-based films for magnonic devices
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-6509-5782
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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.

Place, publisher, year, edition, pages
2015. Vol. 92, no 2, 024427
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-172712DOI: 10.1103/PhysRevB.92.024427ISI: 000358600300006Scopus ID: 2-s2.0-84938936223OAI: oai:DiVA.org:kth-172712DiVA: diva2:850001
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
In thesis
1. Gilbert damping of doped permalloy from first principles calculations
Open this publication in new window or tab >>Gilbert damping of doped permalloy from first principles calculations
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
Gilbert damping, DFT, Permalloy, SPR-KKR, Spin stiffness
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-170344 (URN)978-91-7595-539-1 (ISBN)
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
2. 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. 82 p.
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, LarsDelin, Anna

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