| 1. |
- Akansel, Serkan, et al.
(författare)
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Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films
- 2018
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 51:30
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Frisk, Andreas, et al.
(författare)
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Magnetic and structural characterization of CoFeZr thin films grown by combinatorial sputtering
- 2019
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Ingår i: Physical Review Materials. - 2475-9953. ; 3:7
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Tidskriftsartikel (refereegranskat)abstract
- We report on a detailed investigation of structural and magnetic properties of thin CoFeZr films, produced by combinatorial cosputtering, with compositions in the ranges 30-85 at.% Co, 12-63 at.% Fe, and 4-8 at.% Zr. Extended x-ray absorption fine structure and x-ray diffraction measurements reveal that alloys with a Zr content below 5 at.% are polycrystalline with a bcc structure, while an amorphous morphology is stabilized at Zr contents above 6 at.%. All samples display a growth-induced in-plane uniaxial anisotropy, which is closely related to the Zr concentration gradients across the wafers. A model for the angular dependence of the reduced remanence, including a Gaussian distribution of easy/hard anisotropy axes, is presented and successfully used to fit the data for all samples. The magnetic moments of the polycrystalline films approximately follow the Slater-Pauling curve, and the magnetic moments of the amorphous films follow a similar trend, but with about 20 % lower values. X-ray magnetic circular dichroism measurements show, for the amorphous films, that the Co moments are virtually constant at 1.7(2)μB/atom.
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| 3. |
- George, Sebastian, 1990-
(författare)
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Amorphous Magnetic Materials : A Versatile Foundation for Tomorrow’s Applications
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Amorphous magnetic materials exhibit a number of key differentiating properties with respect to crystalline magnets. In some cases, the differences may simply be in the values of macroscopic properties such as saturation magnetization, coercivity, Curie temperature, and electrical conductivity. Other cases are more fundamental, such as the possibility for many amorphous alloys to be produced with nearly arbitrary composition, something that is not always possible in crystal structures that may only be stable for certain specific compositions.Fundamentally, these properties arise due to the disordered arrangement of atoms in amorphous materials. However, this structure is challenging to probe and characterize, either experimentally or theoretically. A significant contribution of this thesis is the development of a new approach for studying the local atomic structure of amorphous materials, specifically amorphous SmCo and FeZr alloys. The strategy combines extended x-ray absorption spectroscopy (EXAFS) measurements with stochastic quenching (SQ) simulations in a way that provides more information than either method can offer alone. Additionally, this approach offers the potential for identifying any shortcomings in the theoretical models obtained via SQ.Having an accurate model of the atomic arrangement is not, however, a prerequisite for developing technical applications of amorphous magnetic materials. For that, it is sufficient to quantify those macroscopic properties that are relevant for a given application. Such is the value of the magnetic characterization of amorphous TbCo and CoFeZr alloy thin films presented here. Both investigations used methods such as vibrating sample magnetometry (VSM) and magneto-optic Kerr effect (MOKE) measurements to highlight the high tunability of the magnetic properties in these materials, which can be achieved simply by changing the chemical composition.The final portion of this thesis examines what can be achieved by combining amorphous SmCo and TbCo alloys together in bilayer structures. This is a step away from the alloy characterization studies, as it focuses on how new properties can be realized when multiple materials are brought together. MOKE measurements were used to identify the conditions under which the bilayers spontaneously become magnetized parallel to the film plane versus when the TbCo magnetization begins to tilt out of the plane. Further investigation combining x-ray circular magnetic dichroism (XMCD) measurements and micromagnetic simulations provided a depth-resolved model of the magnetization throughout the bilayers in the presence of a broad range of external field strengths and directions. These models also showed that the local magnetization just above and just below the SmCo/TbCo interface can be aligned either parallel or antiparallel to one another simply by varying the TbCo composition. This discovery offers a novel method for controlling the magnetic behavior in these materials, and may well be useful for all-optical switching or spintronics applications where amorphous TbCo alloys have already drawn attention.
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| 4. |
- George, Sebastian, 1990-
(författare)
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Energy and Angle Resolved Reflectivity of Plasmonic Nanostructures
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- It has been apparent for some time that desirable plasmonic properties can be produced by combining certain component materials into a variety of nanometer-scale structures. A logical next step would be to develop the ability to actively tune the plasmonic properties of a particular nanostructured material. Exploration of such active tuning methods is at the forefront of plasmonics research. One such technique may be to make use of the magnetization within the material, controlled via external field, in order to alter the conditions necessary for plasmon excitation. Presented here are preliminary measurements of reflectivity for one such nanostructured material-a Co film patterned with a hexagonal lattice of holes. Such reflectivity measurements are useful in determining the optimal conditions for plasmon excitation in a sample, but are often limited to only a few wavelengths of incident light. Use of a white light source and spectrometer allows for resolution in both incidence angle and incident energy. Different polarizations of light as well as different incidence directions relative to the hole lattice are considered.
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| 5. |
- George, Sebastian, 1990-, et al.
(författare)
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Local structure in amorphous SmxCo1-x : a combined experimental and theoretical study
- 2020
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 55, s. 12488-12498
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Tidskriftsartikel (refereegranskat)abstract
- Using a combination of extended X-ray absorption fine structure measurements, stochastic quenching (SQ) calculations and Voronoi tessellation analysis, the local atomic environments in thin films of amorphous SmxCo1−x (x= 0.10, 0.22 and 0.35) are investigated and also compared with crystalline stoichiometric Sm–Co alloys of similar compositions. It is found that the variations in local environment around Co atoms in the amorphous films increase with increasing x and that none of the films exhibit any pronounced short-range order around the Sm atoms. There are, however, signs of clustering of Sm atoms in the SQ-generated simulated amorphous materials. Furthermore, good agreement is observed between experimentally obtained parameters, e.g., interatomic distances and coordination numbers, and those extracted from the simulated alloys. This is a strong indication that SQ provides a powerful route to reliable local structure information for amorphous rare earth–transition metal alloys and that it could be used for designing materials with properties that meet the demands of specific applications.
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| 6. |
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| 7. |
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| 8. |
- Muscas, Giuseppe, et al.
(författare)
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Unveiling the local structure of the amorphous metal Fe(1−x)Zrx combining first-principles-based simulations and modelling of EXAFS spectra
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous alloys exhibit useful properties such as the excellent soft magnetic behaviour of Fe-based metallic glasses. The detailed structure of amorphous Fe(1−x)Zrx with x = 0.07, 0.10, and 0.20 is in this work explored through a synergetic combination of atomistic simulations and experimental characterisation. Thin-film samples were investigated using X-ray diffraction and extended X-ray absorption fine structure (EXAFS), while the corresponding atomic structures were simulated using an efficient first-principles-based method called stochastic quenching (SQ). The simulated local atomic arrangements are investigated by constructing the radial- and angular-distribution functions, as well as by Voronoi tesselation. The radial distribution functions are then used to construct a model to fit simultaneously the experimental EXAFS data of multiple samples with different compositions, creating a simple yet accurate description of the atomic structures valid for any composition in the range x = 0.07 to 0.20, using a minimal number of free parameters. This approach significantly improves the accuracy of the fitted parameters and allows us to relate the compositional dependence of the amorphous structures with the magnetic properties. The proposed EXAFS fitting process can be generalised to other amorphous systems, contributing to the understanding of structure-property relationships and the development of amorphous alloys with tailored functional properties.
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| 9. |
- Saini, Apurve, et al.
(författare)
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Layering of magnetic nanoparticles at amorphous magnetic templates with perpendicular anisotropy
- 2020
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 16:33, s. 7676-7684
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Tidskriftsartikel (refereegranskat)abstract
- We reveal the assembly of magnetite nanoparticles of sizes 5 nm, 15 nm and 25 nm from dilute water-based ferrofluids onto an amorphous magnetic template with out-of-plane anisotropy. From neutron reflectometry experiments we extract density profiles and show that the particles self-assemble into layers at the magnetic surface. The layers are extremely stable against cleaning and rinsing of the substrate. The density of the layers is determined by and increases with the remanent magnetic moment of the particles.
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