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Magnetization Dynamics in Ferromagnetic Thin Films: Evaluation of Different Contributions to Damping in Co2FeAl and FeCo Film Structures
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Static and dynamic magnetic properties of Co2FeAl and Fe65Co35 alloys have been investigated. Co2FeAl films were deposited at different temperatures and the deposition parameters were optimized with respect to structural and magnetic properties. As a result, a film with B2 crystalline phase was obtained without any post-annealing process. A lowest magnetic damping parameter of  was obtained for the film deposited at 573K. This obtained low value is comparable to the lowest values reported in research literature.  After optimizing the deposition parameters of this alloy, different seed layers and capping layers were added adjacent to the Co2FeAl layer and the effect of these layers on the magnetic relaxation was investigated. In addition to adding nonmagnetic layers to Co2FeAl, the dependence of the magnetic damping parameter with respect to the thickness of Co2FeAl was investigated by depositing films with different thicknesses. A temperature dependent study of the magnetic damping parameter was also performed and the measured damping parameters were compared with theoretically calculated intrinsic Gilbert damping parameters. Different extrinsic contributions to the magnetic damping, such as two magnon scattering, spin pumping, eddy-current damping and radiative damping, were identified and subtracted from the experimentally obtained damping parameter. Hence, it was possible to obtain the intrinsic damping parameter, that is called the Gilbert damping parameter.

In the second part of the thesis, Fe65Co35 alloys were investigated in terms of static and dynamic magnetic properties. Fe65Co35 films were deposited without and with different seed layers in order to first understand the effect of the seed layer on static magnetic properties of the films, such as the coercivity of the films. Then the films with seed layers yielding the lowest coercivity were investigated in terms of dynamic magnetic properties. Fe65Co35 films with different rhenium dopant concentrations and with ruthenium as the seed and capping layer were also investigated. The purpose of this study was to increase the damping parameter of the films and an increase of about ~230% was obtained by adding the dopant to the structure. This study was performed at different temperatures and after subtraction of the extrinsic contributions to the damping, the experimental values were compared with theoretically calculated values of the Gilbert damping parameter. During the thesis work, magnetic looper and superconducting quantum interference device magnetometers set-ups were used for static magnetic measurements and cavity, broadband in-plane and broadband out-of-plane ferromagnetic resonance set-ups were used for dynamic measurements.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 74
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1644
Keywords [en]
spintronics, Gilbert damping parameter, magnetization dynamics, ferromagnetic resonance, Heusler alloys, magnetic thin films
National Category
Condensed Matter Physics Engineering and Technology Other Engineering and Technologies
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-345856ISBN: 978-91-513-0268-3 (print)OAI: oai:DiVA.org:uu-345856DiVA, id: diva2:1189797
Public defence
2018-05-03, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2018-04-09 Created: 2018-03-12 Last updated: 2018-11-22
List of papers
1. Thickness dependent enhancement of damping in Co2FeAl/β-Ta thin films
Open this publication in new window or tab >>Thickness dependent enhancement of damping in Co2FeAl/β-Ta thin films
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 13, article id 134421Article in journal (Refereed) Published
Abstract [en]

In the present work Co2FeAl (CFA) thin films were deposited by ion beam sputtering on Si (100) substrates at the optimized deposition temperature of 300°C. A series of CFA films with different thickness (tCFA ); 8, 10, 12, 14, 16, 18 and 20 nm were prepared and all samples were capped with a 5 nm thick b-Ta layer. The thickness dependent static and dynamic properties of the films were studied by SQUID magnetometry, in-plane as well as out-of-plane broadband VNA-FMR measurements and angle dependent cavity FMR measurements. The saturation magnetization and the coercive field were found to be weakly thickness dependent and lie in the range 900 – 950 kA/m and 0.53 – 0.87 kA/m, respectively. The effective damping parameter ( αeff) extracted from in-plane and out-of-plane FMR results reveal a 1/tCFA dependence, the values for the in-plane αeff being larger due to two-magnon scattering (TMS). The origin of the αeff thickness dependence is spin pumping into the non-magnetic b-Ta layer and in case of the in-plane  αeff also a thickness dependent TMS contribution. From the out-of-plane FMR results, it was possible to disentangle the different contributions to αeff   and to the extract values for the intrinsic Gilbert damping (αG ) and the effective spin-mixing conductance (g_eff^↑↓ ) of the CFA/ b-Ta interface, yielding αG=1.1X10-3 and g_eff^↑↓=2.90x1019 m-2.

Place, publisher, year, edition, pages
American Physical Society, 2018
Keywords
Magnetization dynamics, magnetic thin films, Gilbert damping, ferromagnetic resonance
National Category
Condensed Matter Physics Materials Engineering
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-345848 (URN)10.1103/PhysRevB.97.134421 (DOI)000430544300002 ()
Funder
Knut and Alice Wallenberg Foundation, 2012.0031
Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2018-06-26Bibliographically approved
2. Enhanched Gilbert Damping in Re doped FeCo Films: A combined experimental and theoretical study
Open this publication in new window or tab >>Enhanched Gilbert Damping in Re doped FeCo Films: A combined experimental and theoretical study
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effects of rhenium doping in the range 0 – 10 at% on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first principles electronic structure calculations focussing on the change of the saturation magnetization (Ms ) and the Gilbert damping parameter (α ). Both experimental and theoretical results show that Ms decreases with increasing Re doping level, while at the same time α increases.  The experimental low temperature saturation magnetic induction exhibits a 29% decrease, from 2.31T to 1.64T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 2.7X103, which is close to the Gilbert damping parameter extracted from the theoretical calculations. The room temperature experimental value for the damping parameter increases to  9X103 when doping with 10 at% Re; the corresponding increase of the Gilbert damping parameter obtained from theoretical calculations is 7.3X103. Both experimental and theoretical values for the damping parameter weakly decrease with decreasing temperature.

Keywords
Magnetization dynamics, magnetic thin films, Gilbert damping, ferromagnetic resonance
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-345854 (URN)
Funder
Knut and Alice Wallenberg Foundation, 2012.0031
Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2018-03-12
3. Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films
Open this publication in new window or tab >>Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films
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2018 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 30, article id 305001Article in journal (Refereed) Published
Abstract [en]

Fe65Co35 thin films have been deposited on SiO2 substrates using sputtering technique with different choices of seed layer; Ru, Ni82.5Fe17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni82.5Fe17.5 and Rh. Adding these seed layers, the coercivity of the Fe65Co35 films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0X10-3 and 4.5X10-3 were obtained from in-plane and out-of-plane measurements, respectively, for as prepared samples, values that were reduced to 6.5X10-3 and 4.0X10-3 for annealed samples.

Keywords
Magnetization dynamics, magnetic thin films, Gilbert damping, ferromagnetic resonance
National Category
Condensed Matter Physics Engineering and Technology
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-345853 (URN)10.1088/1361-6463/aaccc0 (DOI)000437408700001 ()
Funder
Knut and Alice Wallenberg Foundation, 2012.0031
Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2018-10-12Bibliographically approved
4. Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering
Open this publication in new window or tab >>Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering
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2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 28692Article in journal (Refereed) Published
Abstract [en]

The influence of growth temperature T-s (300-773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl (CFA) thin films on industrially important Si(100) substrate. The B2 type magnetic ordering is established in these films based on the clear observation of the (200) diffraction peak. These ion beam sputtered CFA films possess very small surface roughness of the order of subatomic dimensions (<3 angstrom) as determined from the fitting of XRR spectra and also by AFM imaging. This is supported by the occurrence of distinct Kiessig fringes spanning over the whole scanning range (similar to 4 degrees) in the x-ray reflectivity (XRR) spectra. The Gilbert damping constant alpha and effective magnetization 4 pi M-eff are found to vary from 0.0053 +/- 0.0002 to 0.0015 +/- 0.0001 and 13.45 +/- 00.03 kG to 14.03 +/- 0.04 kG, respectively. These Co2FeAl films possess saturation magnetization ranging from 4.82 +/- 0.09 to 5.22 +/- 0.10 mu(B)/f.u. consistent with the bulk L2(1)-type ordering. A record low alpha-value of 0.0015 is obtained for Co2FeAl films deposited on Si substrate at T-s similar to 573 K.

National Category
Other Physics Topics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-299867 (URN)10.1038/srep28692 (DOI)000378783900001 ()27357004 (PubMedID)
Available from: 2016-07-28 Created: 2016-07-28 Last updated: 2018-03-12Bibliographically approved
5. Static and dynamic properties of Co2FeAl thin films: Effect of MgO and Ta as capping layers
Open this publication in new window or tab >>Static and dynamic properties of Co2FeAl thin films: Effect of MgO and Ta as capping layers
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2017 (English)In: 61ST DAE-SOLID STATE PHYSICS SYMPOSIUM, 2017, Vol. 1832, article id 080007-1Conference paper, Published paper (Refereed)
Abstract [en]

The influence of MgO and Ta capping layers on the static and dynamic magnetic properties of Co2FeAl (CFA) Heusler alloy thin films has been investigated. It is observed that the CFA film deposited with MgO capping layer is preeminent compared to the uncapped or Ta capped CFA film. In particular, the magnetic inhomogeneity contribution to the ferromagnetic resonance line broadening and damping constant are found to be minimal for the MgO capped CFA thin film i.e., 0.12±0.01 Oe and 0.0074±0.00014, respectively. The saturationmagnetization was found to be 960±25emu/cc.

Series
AIP Conference Proceedings, ISSN 0094-243X
Keywords
Heusler alloy, MgO, Gilbert damping
National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-332482 (URN)10.1063/1.4980467 (DOI)000412824400289 ()978-0-7354-1500-3 (ISBN)
Conference
61st DAE-Solid State Physics Symposium, DEC 26-30, 2016, KIIT Univ, Bhubaneswar, INDIA
Projects
Knut and Alice Wallenberg (KAW) Foundation, Grant No. KAW 2012.0031.
Available from: 2017-10-27 Created: 2017-10-27 Last updated: 2018-03-29Bibliographically approved
6. Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order
Open this publication in new window or tab >>Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 224425Article in journal (Refereed) Published
Abstract [en]

Half-metallicity and low magnetic damping are perpetually sought for spintronics materials, and full Heusler compounds in this respect provide outstanding properties. However, it is challenging to obtain the well-ordered half-metallic phase in as-deposited full Heusler compound thin films, and theory has struggled to establish a fundamental understanding of the temperature-dependent Gilbert damping in these systems. Here we present a study of the temperature-dependent Gilbert damping of differently ordered as-deposited Co2FeAl full Heusler compound thin films. The sum of inter- and intraband electron scattering in conjunction with the finite electron lifetime in Bloch states governs the Gilbert damping for the well-ordered phase, in contrast to the damping of partially ordered and disordered phases which is governed by interband electronic scattering alone. These results, especially the ultralow room-temperature intrinsic damping observed for the well-ordered phase, provide fundamental insights into the physical origin of the Gilbert damping in full Heusler compound thin films.

Place, publisher, year, edition, pages
American Physical Society, 2017
Keywords
Gilbert damping, full Heusler compound, Temperature Dependent Gilbert damping, Thin Films, Density of states
National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-337305 (URN)10.1103/PhysRevB.96.224425 (DOI)000418572700007 ()
Funder
Knut and Alice Wallenberg Foundation, KAW 2012.0031Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology, GGS1403ASwedish National Infrastructure for Computing (SNIC)
Available from: 2017-12-22 Created: 2017-12-22 Last updated: 2018-03-12

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