| 51. |
- Callini, Elsa, et al.
(författare)
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Complex and liquid hydrides for energy storage
- 2016
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 122:4
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Tidskriftsartikel (refereegranskat)abstract
- The research on complex hydrides for hydrogen storage was initiated by the discovery of Ti as a hydrogen sorption catalyst in NaAlH4 by Boris Bogdanovic in 1996. A large number of new complex hydride materials in various forms and combinations have been synthesized and characterized, and the knowledge regarding the properties of complex hydrides and the synthesis methods has grown enormously since then. A significant portion of the research groups active in the field of complex hydrides is collaborators in the International Energy Agreement Task 32. This paper reports about the important issues in the field of complex hydride research, i.e. the synthesis of borohydrides, the thermodynamics of complex hydrides, the effects of size and confinement, the hydrogen sorption mechanism and the complex hydride composites as well as the properties of liquid complex hydrides. This paper is the result of the collaboration of several groups and is an excellent summary of the recent achievements.
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| 52. |
- Carstensen, Hauke
(författare)
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Self-assembly of magnetic particles
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-assembly is the spontaneous formation of larger structures from small building blocks. This process is driven and determined by the interactions between the constituents. Examples of self assembly are found almost everywhere and, in particular, biological systems in general rely on a hierarchical formation of structures over a range of length scales. Technologically, self-assembly can be used to form mesoscopic structures and artificial crystals. In the case of particles with micrometer size suspended in a liquid phase, it is possible to use optical microscopy for the the investigation of self-assembly.In this thesis, the self-assembly of microbeads with tunable magnetic interactions is studied, based on the statistic analysis of microscope images and computer simulations. Magnetic and non-magnetic microbeads are suspended in a ferrofluid, which is a dispersion of magnetic nanoparticles in water. As a result, the magnetic properties of the microbeads in the ferrofluid are altered and can be described by effective magnetic susceptibilities and magnetic dipole moments, which can be tuned continuously. The liquid is confined between glass slides and effectively the microbeads are studied in a 2D geometry under a magnetic field, applied either in- or out-of-plane. The resulting structures are detected by image analysis algorithms, analyzed and correlated to the dipolar interaction between the beads, as well as to macroscopic quantities, like the particle density and ratio. For the in-plane field a phase transition from square to hexagonal lattice is observed. This phase transition is explained by the change in dipole interaction between the microbeads as the moments change from anti-parallel to parallel alignment. For the out-of-plane field the situation becomes diverse and more phases appear. It turns out that the phase formation in this case is strongly dependent on the bead ratio, density and interactions.We identify regions in the phase diagram, where isolated beads, percolated structures, and crystals dominate. To cover a wide parameter range the experiments are complemented by computer simulations. The tools developed in this thesis enable us to construct phase diagrams extracted from direct imaging and dependence on the extracted relevant parameters.
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| 53. |
- Carvalho de Melo Rodrigues, Debora, et al.
(författare)
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Prediction of a Larger Local Magnetic Anisotropy in Permalloy
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- By means of relativistic, first principles calculations, we investigate the microscopic origin of the vanishingly low magnetic anisotropy of Permalloy. Analyzing the local magnetic anisotropy of these alloys, we find that it can be several orders of magnitude larger than that of the bulk sample, and at least one order of magnitude larger than that of Fe or Ni. We discuss these results in terms of local symmetries of the alloy, and point out that an analysis based on perturbation theory has the spin-orbit coupling entering as a second-order term, as opposed to the naively expected fourth order contribution. The relevance for these findings in experiments, e.g. using pump-probe investigations, is discussed, as well as the implications for building effective spin-Hamiltonians of Permalloy.
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| 54. |
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| 55. |
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| 56. |
- Chacon, C., et al.
(författare)
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Growth and Hydrogen uptake of Mg-Y thin films
- 2005
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 97, s. 104903-
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Tidskriftsartikel (refereegranskat)abstract
- Wedged Mg–Y films with compositions ranging from pure Mg to Mg0.83Y0.17 were grown by dc-magnetron sputtering and hydrogenated. Mg1–xYx forms a substitutional alloy, ranging from 0 to at least 17 at. % in thin films. The c lattice parameter of the film containing 17 at. % of yttrium is determined to be approximatively 1% larger than in pure Mg. Upon exposure to 1 bar of hydrogen at 300 K, the samples switch from shiny metals to colorless semiconductor. Different characteristic hydrogen depth distributions are found for different Y concentrations. At low yttrium contents, a large concentration gradient is observed, with the highest hydrogen concentration close to the Pd/Mg1–xYx interface. For yttrium concentrations larger than 7 at. %, the obtained hydrogen distribution is almost independent of depth. The optical band gap is determined to be 3.6 eV, for all the Y concentrations. The optical transmission is found to decrease for increasing Y content, which is associated with an incomplete hydride formation in the films.
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| 57. |
- Chioar, Ioan-Augustin, et al.
(författare)
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Modular magneto-optical diffractometer for the characterization of magnetoplasmonic crystals
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report on the development of a modular magneto-optical diffractometer designed to measure the optical and magneto-optical properties of nanostructured magnetoplasmonic crystals. The system uses monochromatic, coherent light beams with defined polarization states, for the energy- and angular-dependent measurement of reflected and transmitted beams. Polarization analysis instrumentation further enables the detailed characterisation of the polarization state of the light after the interaction with the magnetoplasmonic crystals. The magneto-optical activity is measured with the help of a quadrupole coil system, allowing for the application of magnetic fields in the plane of the samples. The instrument’s versatile design provides a toolbox of methods capable of capturing a far-field description of the optical and magneto-optical response of magnetoplasmonic crystals. We demonstrate its functionality and utility for the case of a Ni-antidot crystal.
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| 58. |
- Chioar, Ioan-Augustin, et al.
(författare)
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Steering light with magnetic textures
- 2022
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 120:3
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Tidskriftsartikel (refereegranskat)abstract
- We study the steering of visible light using a combination of magneto-optical effects and the reconfigurability of magnetic domains in yttrium-iron garnet films. The spontaneously formed stripe domains are used as a field-controlled optical grating, allowing for active spatiotemporal control of light. We discuss the basic ideas behind the approach and provide a quantitative description of the field dependence of the obtained light patterns. Finally, we calculate and experimentally verify the efficiency of our magneto-optical grating.
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| 59. |
- Ciuciulkaite, Agne, et al.
(författare)
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Collective magnetization dynamics in nanoarrays of thin FePd disks
- 2019
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 99:18
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Tidskriftsartikel (refereegranskat)abstract
- We report on the magnetization dynamics of a square array of mesoscopic disks, fabricated from an iron palladium alloy film. The dynamics properties were explored using ferromagnetic resonance measurements and micromagnetic simulations. The obtained spectra exhibit features resulting from the interactions between the disks, with a clear dependence on both temperature and the direction of the externally applied field. We demonstrate a qualitative agreement between the measured and calculated spectra. Furthermore, we calculated the mode profiles of the standing spin waves excited during time-dependent magnetic field excitations. The resulting maps confirm that the features appearing in the ferromagnetic resonance absorption spectra originate from the temperature- and directional-dependent interdisk interactions.
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| 60. |
- Čiučiulkaitė, Agnė, MSc, 1991-
(författare)
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Dynamics in magnetic metamaterials
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metamaterials are artificially created structures with properties that are not found in nature. They can be tailored to achieve desired response to external excitations such as external electric and magnetic fields, as well as to enhance materials’ optical or magnetic activity. Magnetic metamaterials comprised of arrays of sub-micrometer sized magnetic elements, can be used for a range of different applications, such as magnonic crystals and building blocks for magnetic memory elements.In this work, pathways for tuning magnetization dynamics are explored. Different magnetic metamaterials containing arrays of sub-micrometer sized elements, refered to as nanomagnets, were used as model systems for these explorations. The nano-magnets comrising these arrays are of two kinds: XY-rotors, with a magnetization direction rotating freely in-plane of a disk, and Ising-like spins, pointing along either of the two allowed magnetization directions. The Ising-like spins can be realized in either in-plane or out-of-plane magnetized materials.Collective magnetization dynamics were investigated in square arrays of coupled nanomagnets. Studies revealed that nanomagnet’s magnetization state cannot always be approximated by a ridig mesospin approximation. Instead, it was demonstrated that upon an external perturbation, such as an external magnetic or thermal field, internal magnetization experience texture excitations. The observed texture excitations have implications on the nanomagnet coupling in an array.Arrays, where collective phenomena emerge via excited plasmon resonances, were used for investigations of light-induced dynamics processes. Studies revealed importance of an array design for the observation of magneto-optical activity enhancement and more eÿcient ultrafast magnetization dynamics. It was reported that in arrays containing truncated Au nanocones with TbCo tip, enhancement of TbCo demagnetization can be achieved via resonant light illumination.Utilizing the array concept and magnetic anisotropy of a material, it is possible to create metamaterials, where a range of magnetization dynamics regimes can be investigated. Inter-element spacing defines on which lengthscale the nanomagnets will be coupled and which effects can be utilized for tuning system’s magneto-optical response and excited magnetization dynamics.
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