| 1. |
- Anyfantis, Dimitrios I., et al.
(författare)
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Growth, Magnetic Anisotropies and Exchange Bias of Thin Ni0.95Fe0.05/NiFeO Multilayers
- 2022
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Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Ni0.95Fe0.05/NiFeO multilayers were fabricated by radio frequency magnetron sputtering and natural oxidation. Doping of Ni by only 5 at. % Fe results in enhanced layering quality as X-ray reflectivity reveals. Due to magnetostatic anisotropy, the multilayers were found to be in-plane magnetized. The influence of mild thermal annealing (T = 525 K) on the magnetic properties of NiFe/NiFeO multilayers is also investigated. Annealing results in the enhancement of perpendicular magnetic anisotropy, mainly due to an increase in the uniaxial volume anisotropy term. Temperature-dependent hysteresis measurements between 4-400 K revealed considerable enhancement of coercivity and appearance of exchange bias effect.
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| 2. |
- Anyfantis, Dimitrios, I, et al.
(författare)
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Unexpected Development of Perpendicular Magnetic Anisotropy in Ni/NiO Multilayers After Mild Thermal Annealing
- 2019
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Ingår i: IEEE Magnetics Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1949-307X .- 1949-3088. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- We report on the significant enhancement of perpendicular magnetic anisotropy of Ni/NiO multilayers after mild annealing up to 90 min at 250 degrees C. Transmission electron microscopy shows that after annealing, a partial crystallization of the initially amorphous NiO layers occurs. This turns out to be the source of the anisotropy enhancement. Magnetic measurements reveal that even multilayers with Ni layers as thick as 7 nm, which in the as-deposited state showed in-plane anisotropy with square hysteresis loops, show reduced in-plane remanence after thermal treatment. Hysteresis loops recorded with the field in the normal-to-film-plane direction provide evidence for perpendicular magnetic anisotropy with up and down magnetic domains at remanence. A plot of effective uniaxial magnetic anisotropy constant times individual Ni layer thickness as a function of individual Ni layer thickness shows a large change in the slope of the data attributed to a drastic change of volume anisotropy. Surface anisotropy showed a small decrease because of some layer roughening introduced by annealing.
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| 3. |
- Barnasas, A., et al.
(författare)
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Quantum confinement effects of thin ZnO films by experiment and theory
- 2020
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : ELSEVIER. - 1386-9477 .- 1873-1759. ; 120
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Tidskriftsartikel (refereegranskat)abstract
- Thin ZnO films with thickness ranging between 2 and 300 nm have been grown on quartz, Corning glass and Si (100) substrates by radio frequency magnetron sputtering. The film thickness was determined by pre-calibrated quartz balance with the help of x-ray reflectivity measurements. X-ray diffraction experiments revealed the formation of highly-textured hexagonal ZnO. Ultraviolet-visible light absorption spectroscopy has shown a "blue shift" of the direct band gap of ZnO. The experimental results are interpreted as evidences of quantum confinement effects. This is supported by theoretical predictions of the optical gap, which was calculated in the framework of effective mass approximation by solving the two particle (electron and hole) Hartree-Fock equations. The observed fair agreement between theoretical and experimental results corroborates the quantum confinement interpretation.
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| 4. |
- Bylin, Johan, et al.
(författare)
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One-shot pair distribution functions of thin films using lab-based x-ray sources
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate the feasibility of obtaining accurate pair distribution functions of thin amorphous films down to 80 nm, using modern laboratory-based x-ray sources. The pair distribution functions are obtained using a single diffraction scan (one-shot) without the requirement of additional scans of the substrate or of the air. By using a crystalline substrate combined with an oblique scattering geometry, most of the Bragg scattering of the substrate is avoided, rendering the substrate Compton scattering the primary contribution. By utilizing a discriminating energy filter, available in the latest generation of modern detectors, we demonstrate that the Compton intensity can further be reduced to negligible levels at higher wavevector values. We minimize scattering from the sample holder and the air by the systematic selection of pixels in the detector image based on the projected detection footprint of the sample and the use of a 3D printed sample holder. Finally, x-ray optical effects in the absorption factors and the ratios between the Compton intensity of the substrate and film are taken into account by using a theoretical tool that simulates the electric field inside the film and the substrate, which aids in planning both the sample design and measurement protocol.
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| 5. |
- Carstensen, Hauke, et al.
(författare)
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Self-assembly and percolation in two dimensional binary magnetic colloids
- 2022
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 18:33, s. 6222-6228
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Tidskriftsartikel (refereegranskat)abstract
- We study the self-assembly of branching-chain networks and crystals in a binary colloidal system with tunable interactions. The particle positions are extracted from microscopy images and order parameters are extracted by image processing and statistical analysis. With these, we construct phase diagrams with respect to particle density, ratio and interaction. In order to draw a more complete picture, we complement the experiments with computer simulations. We establish a region in the phase diagram, where bead ratios and interactions are symmetric, promoting percolated structures.
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| 6. |
- 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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| 7. |
- Carstensen, Hauke, et al.
(författare)
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Statistical analysis of phase formation in 2D colloidal systems
- 2018
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Ingår i: The European Physical Journal E Soft matter. - : SPRINGER. - 1292-8941 .- 1292-895X. ; 41:1
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal systems offer unique opportunities for the study of phase formation and structure since their characteristic length scales are accessible to visible light. As a model system the two-dimensional assembly of colloidal magnetic and non-magnetic particles dispersed in a ferrofluid (FF) matrix is studied by transmission optical microscopy. We present a method to statistically evaluate images with thousands of particles and map phases by extraction of local variables. Different lattice structures and long-range connected branching chains are observed, when tuning the effective magnetic interaction and varying particle ratios.
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| 8. |
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| 9. |
- 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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| 10. |
- 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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| 11. |
- 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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| 12. |
- 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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| 13. |
- Ciuciulkaite, Agne, MSc, 1991-, et al.
(författare)
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Impact of the magnetic layer crystal growth optimization on the THzemission from spintronic Fe/Pt emitters
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigate the THz emission characteristics of ferromagnetic/non-magnetic metallic heterostructures, focusing on thin Fe/Pt bilayers. In particular, we report on the impact of optimized crystal growth of the epitaxial Fe layers on the THz emission amplitude and spectral bandwidth. We demonstrate a 5 % enhancement of the emitted intensity, related to reduced spin scattering and higher interface transmission. Our work provides a pathway for devicing optimal spintronic THz emitters based on epitaxial Fe. It also highlights how THz emission measurements can be utilized to characterize the changes in out-of-equilibrium spin current dynamics in metallic heterostructures, driven by subtle structural refinement.
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| 14. |
- Ciuciulkaite, Agne, MSc, 1991-, et al.
(författare)
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Magnetic and all-optical switching properties of amorphous TbxCo100-x alloys
- 2020
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Ingår i: Physical Review Materials. - : American Physical Society (APS). - 2475-9953. ; 4:10
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous TbxCo100-x magnetic alloys exhibit a list of intriguing properties, such as perpendicular magnetic anisotropy, high magneto-optical activity, and magnetization switching using ultrashort optical pulses. Varying the Tb:Co ratio in these alloys allows for tuning properties such as the saturation magnetic moment, coercive field, and the performance of light-induced magnetization switching. In this paper, we investigate the magnetic, optical, and magneto-optical properties of various TbxCo100-x thin-film alloy compositions. We report on the effect the choice of different seeding layers has on the structural and magnetic properties of TbxCo100-x layers. We also demonstrate that for a range of alloys, deposited on fused silica substrates, with Tb content of 24-30 at. %, helicity-dependent all-optical switching of magnetization can be achieved, albeit in a multishot framework. We explain this property to arise from the helicity-dependent laser-induced magnetization on the Co sublattice due to the inverse Faraday effect. Our paper provides an insight into material aspects for future potential hybrid magnetoplasmonic TbCo-based architectures.
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| 15. |
- Ciuciulkaite, Agne, MSc, 1991-
(författare)
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The interaction of light and magnetism in the TbxCo100-x system
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Development of the faster and denser magnetic memory storage elements has been an active area of research since early 20th century. The path of research on magnetization manipulation began with firstly changing the magnetization state of a medium in an external magnetic field, then heating of a medium and magnetizing with a permanent magnet was explored, while the latest efforts have been focused on switching the magnetization only by a polarized laser light. Nowadays due to the technological advancement of lasers and material fabrication methods, the search and development process of magnetic memory elements is much faster. The implementation of such technologies, however, relies on finding suitable magnetic materials which would allow for a fast magnetization writing and read-out processes and would remain magnetized, even with the reduced dimensions. Ferrimagnetic rare Earth - transition metal (RE-TM) alloys have been used for fabricating magneto-optical recording media already since the 1990’s. Relatively recently, in 2007, it was demonstrated that the ferrimagnetic GdFeCo alloy magnetization state can be switched using only circularly polarized laser light. Hence, ferrimagnetic RE-TMalloys could be suitable candidates for all-optical light-induced magnetization switching (AOS), without any external magnetic field. Another combination of RE-TM alloys that was shown to exhibit AOS is ferrimagnetic amorphous alloys containing terbium and cobalt (Tb:Co). They have attracted attention due to their strong out-of-plane magnetic anisotropy, high magneto-optical activity and amorphicity, which makes them attractive from a fabrication point of view since a variety of substrates and buffer layers could be used for growing such layers. In this Thesis, TbCo alloys are investigated in order to examine how the magnetic, optical and magneto-optical properties could be tuned by varying the elemental ratio and film thickness. The main question that was addressed here was whether such a system is suitable for fabrication of nanosized magnetic elements as the building blocks for the magnetic memory applications. TbCo alloys were prepared as thin films by magnetron co-sputtering method onto different substrates and buffer layers. Films were characterized using a variety of techniques such as an ion beam analysis, an x-ray reflectivity and diffraction, and magneto-optical characterization techniques. It was observed that the properties of such alloys depend not only on the Tb:Co ratio but also on the film thickness and an underlying buffer layer. Magnetization compensation point, at which the magnetization of a film is zero, as in an antiferromagnet, can be modified depending on the buffer layer. All-optical switching (AOS) of magnetization experiments were performed on the fabricated samples. It was determined that AOS with at least 50-100 laserpulses can be achieved for the films grown directly onto fused silica substrates and with the compositions above the magnetization compensation point at room temperature, in the range of 24 - 30 at.% Tb. In the Outlook, the initial efforts of patterning the films into the arrays of nanosized elements are presented. It is demonstrated that after the lithographic patterning of the films, the resulting nanosized elements remained out-of-plane magnetized. In this work it is shown that the ferrimagnetic TbCo alloy system is a potential candidate material for bothfacilitating AOS and the fabrication of arrays of nanomagnets. Combining the TbCo alloys,which show AOS, together with a suitable buffer layer and patterning the hybrid structure,could enable selective element-by-element magnetization switching for the magnetic memorystorage devices.
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| 16. |
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| 17. |
- Denoel, Fernand
(författare)
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Electronic and magnetic properties of Tsai quasicrystals and their approximants under pressure
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quasicrystals constitute a special category of crystals exhibiting long-range order without periodicity. This strange feature allows them to exhibit rotational symmetries prohibited in regular crystals, such as 5-, 8-, 10- or 12-fold symmetry. Amongst them, icosahedral quasicrystals are the only type that is aperiodic along all 3 dimensions. The present work will focus on Tsai-Type quasicrystals and their approximants, which are the most studied type of icosahedral quasicrystals. We will introduce how they can be generated froma hyperspace perspective, their exotic structure and how it relates to their physical properties. Pressure is a key parameter which can be used to alter the condensed matter properties of a material. By reducing the size of samples and using diamond anvil cells, it is possible to obtain the highest experimentally achievable pressures and collect informations such as magnetization, electrical resistivity or Raman signal. This work will introduce the specialized diamond anvil cells we used to investigate electron transport and magnetization under pressure, explain in details how to circumvent the most common difficulties arising with high pressure setups. and describe how high pressure affects Tsai quasicrystals and approximants in terms of structure and magnetic properties.
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| 18. |
- Droulias, Sotirios A., et al.
(författare)
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Crystal perfection by strain engineering : The case of Fe/V (001)
- 2017
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 636, s. 608-614
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Tidskriftsartikel (refereegranskat)abstract
- We study the effect of bilayer thickness at fixed volume fraction on the structural quality of Fe/V (001)superlattices. We find that such artificial metallic superlattices can be manufactured with excellent crystalquality and layering up to at least 50 Å in repeat distance (K = LFe +LV). For an intended fixed ratio of theconstituents: LFe/LV= 1/7, out-of-plane coherence lengths comparable to the thicknesses of the sampleswere obtained. We evaluate the strain in- and out-of-plane of both layers as a function of the bilayer thicknessand comment on the growth using the framework of linear elasticity theory. We interpret the stabilityof the superlattice against crystal degradation due to the alternating compressive and tensile strain, yieldingclose to ideal lattice matching to the substrate.
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| 19. |
- Gemma, Ryota, et al.
(författare)
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The impact of nanoscale compositional variation on the properties of amorphous alloys
- 2020
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- The atomic distribution in amorphous FeZr alloys is found to be close to random, nevertheless, the composition can not be viewed as being homogenous at the nm-scale. The spatial variation of the local composition is identified as the root of the unusual magnetic properties in amorphous Fe1-xZrx alloys. The findings are discussed and generalised with respect to the physical properties of amorphous and crystalline materials.
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| 20. |
- Ignatova, K., et al.
(författare)
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Reversible exchange bias in epitaxial V2O3/Ni hybrid magnetic heterostructures
- 2022
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 34:49
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Tidskriftsartikel (refereegranskat)abstract
- In this work we present a temperature and angular dependent study of the structural and magnetic properties in highly crystalline V2O3/Ni/Zr magnetic heterostructure films. Our investigation focuses on the coupling between the ferromagnetic Ni layer and V2O3 layer which undergoes an antiferromagnetic/paramagnetic phase transition coupled to the structural phase transition of the material at around 150 K. Structural investigations using x-ray diffraction reveal highly crystalline films of a quality which has previously not been reported in the literature. The Ni layers display an absence of in-plane magnetic anisotropy owing to the highly textured (1 1 1) layering of the Ni films on the underlying V2O3(0 0 0 1) oriented layer. During the transition we observe a strain related enhancement of the coercivity and the onset of a weak exchange bias for cooling under an external magnetic field. Heating the films to above the transition temperature, the exchange bias in the Ni is removed and can be reversed upon subsequent cooling under an inverted external magnetic field. Using temperature dependent polarized neutron reflectometry we investigate the film structure at the interface, capturing the magnetic and nuclear profiles.
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| 21. |
- Kapaklis, Vassilios, 1978-
(författare)
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Magnetizing semiconductors with light
- 2018
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 13:6, s. 438-439
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 22. |
- Kapaklis, Vassilios, 1978-, et al.
(författare)
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Nanolithographic Templates Using Diblock Copolymer Films on Chemically Heterogeneous Substrates
- 2010
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 10:9, s. 6056-6061
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Tidskriftsartikel (refereegranskat)abstract
- The orientation of the lamellae formed by the phase separation of symmetric diblock copolymer thin films is strongly affected by the wetting properties of the polymer blocks with respect to the substrate. On bare silicon wafers the lamellae of polystyrene-b-polymethylmethacrylate thin films tend to order parallel to the wafer surface, with the polymethylmethacrylate block preferentially wetting silicon. We have developed a methodology for inducing the arrangement of lamellae perpendicular to the substrate by using chemically modified substrates. This is done by chemisorbing a self-assembled monolayer of thiol-terminated alkane chains on thin gold films deposited on silicon wafers. We also show that it is possible to spatially control the perpendicular orientation of the lamellae at sub-micron length scales by using simple chemical patterns and etch them, in order to produce nanolithographic templates. This method may be of great technological interest for the preparation of well-defined templates using block copolymer thin films.
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| 23. |
- Kapaklis, Vassilios, 1978-, et al.
(författare)
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Structure and Magnetic Properties of hcp and fcc Nanocrystalline Thin Ni Films and Nanoparticles Produced by Radio Frequency Magnetron Sputtering
- 2010
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 10:9, s. 6024-6028
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Tidskriftsartikel (refereegranskat)abstract
- We report on the growth of thin Ni films by radio frequency magnetron sputtering in Ar-plasma. The growth temperature was about 350 K and the films were deposited on various substrates such as glass, silicon, sapphire and alumina. The thickness of the thinnest films was estimated by the appearance of Kiessig fringes up to about 2 theta = 8 degrees in the small-angle X-ray diffraction pattern, as expected for high-quality atomically-flat thin films. With the help of this, a quartz balance system was calibrated and used for measuring the thickness of thicker samples with an accuracy of better than 5%. Structural characterization via X-ray diffraction and high resolution transmission electron microscopy revealed an Ar-gas pressure window, where single phase hcp Ni films may be grown. The magnetic response of the Ni films was checked at room temperature via a newly established and fully automatic polar magneto-optic Kerr effect magnetometer. The hcp films show no magnetic response. Interestingly, the magnetic saturation field of fcc films deposited at low Ar pressure is comparable to the one of bulk Ni, while the one of fcc films deposited at high Ar pressures is decreased, revealing the presence of residual strain in the films. Finally, it is shown that it is possible to form films which contain magnetic Ni fcc nanoparticles in a non-magnetic hcp matrix, i.e., a system interesting for technological applications demanding a single Ni target for its production.
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| 24. |
- Kapaklis, Vassilios, 1978-, et al.
(författare)
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Violation of Hund’s third rule in structurally disordered ferromagnets
- 2011
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 84:2, s. 024411-
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Tidskriftsartikel (refereegranskat)abstract
- Violation of Hund’s third rule caused by structural disorder is observed for the induced magnetic moment of Zr, using X-ray magnetic circular dischroism. The induced spin and orbital magnetic moments are anti-parallel in the crystalline state, but parallel in an amorphous state of the investi- gated Co- and Fe-based materials. First principles calculations are used to provide physical insight into the dependency of the spin-orbit coupling on the interatomic distance and coordination number.
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| 25. |
- Kumar, Ankit, et al.
(författare)
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Impact of the crystal orientation on spin-orbit torques in Fe/Pd bilayers
- 2020
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 53:35
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Tidskriftsartikel (refereegranskat)abstract
- Spin-orbit torques in ferromagnetic/non-magnetic heterostructures offer more energy-efficient means to realize spin-logic devices; however, their strengths are determined by the heterostructure interface. This work examines the impact of crystal orientation on the spin-orbit torque efficiency in different Fe/Pd bilayer systems. Results from spin torque ferromagnetic resonance measurements evidence that the damping-like torque efficiency is higher in epitaxial than in polycrystalline bilayer structures while the field-like torque is negligible in all bilayer structures. The strength of the damping-like torque decreases with deterioration of the bilayer epitaxial quality. The present finding provides fresh insight for the enhancement of spin-orbit torques in magnetic heterostructures.
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| 26. |
- Liu, H., et al.
(författare)
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Enhanced optical mode coherence in exchange coupled soft magnetic multilayers
- 2022
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 131:21
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Tidskriftsartikel (refereegranskat)abstract
- We report on an all-optical investigation of coupled spin excitation modes in a series of magnetic trilayer structures. Using time-resolved magneto-optic Kerr effect (tr-MOKE) magnetometry, we observe multi-mode coherent spin excitations in Ni81Fe19/Ru/Co49Fe49V2 multi layers even though the tr-MOKE optical detection is sensitive only to the Co49Fe49V2 magnetization dynamics. Frequency shifts of the different modes indicate that the coupling between the Ni(81)Fe(19 a)nd Co49Fe49V2 layers varies from anti-ferromagnetic to ferromagnetic to uncoupled as the Ru spacer layer thickness is increased from 8 & Aring; to 200 & Aring;. The lifetime of the high frequency coherent oscillations in the Co49Fe49V2 layer increases by over 200%-300% even in the case of uncoupled Ni81Fe19 and Co49Fe49V2 layers with a 200 & Aring; thick Ru spacer. The results suggest an additional method to decrease the damping of high-moment alloys in layered magnetic nanostructures. Published under an exclusive license by AIP Publishing.
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| 27. |
- Maccaferri, Nicolò, Dr. 1988-, et al.
(författare)
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Nanoscale magnetophotonics
- 2020
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 127:8
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Tidskriftsartikel (refereegranskat)abstract
- This Perspective surveys the state-of-the-art and future prospects of science and technology employing nanoconfined light (nanophotonics and nanoplasmonics) in combination with magnetism. We denote this field broadly as nanoscale magnetophotonics. We include a general introduction to the field and describe the emerging magneto-optical effects in magnetoplasmonic and magnetophotonic nanostructures supporting localized and propagating plasmons. Special attention is given to magnetoplasmonic crystals with transverse magnetization and the associated nanophotonic non-reciprocal effects and to magneto-optical effects in periodic arrays of nanostructures. We also give an overview of the applications of these systems in biological and chemical sensing, as well as in light polarization and phase control. We further review the area of nonlinear magnetophotonics, the semiconductor spin-plasmonics, and the general principles and applications of opto-magnetism and nano-optical ultrafast control of magnetism and spintronics. © 2020 Author(s).
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| 28. |
- Magnfält, Daniel, et al.
(författare)
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Synthesis of tunable plasmonic metal-ceramic nanocomposite thin films by temporally modulated sputtered fluxes
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:17
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Tidskriftsartikel (refereegranskat)abstract
- The scientific and technological interest for metal-dielectric nanocomposite thin films emanates from the excitation of localized surface plasmon resonances (LSPRs) on the metal component. The overall optical response of the nanocomposite is governed by the refractive index of the dielectric matrix and the properties of the metallic nanoparticles in terms of their bulk optical properties, size, and shape, and the inter-particle distance of separation. In order to tune the film morphology and optical properties, complex synthesis processes which include multiple steps-i. e., film deposition followed by post-deposition treatment by thermal or laser annealing-are commonly employed. In the present study, we demonstrate that the absorption resonances of Ag/AlOxNy nanocomposite films can be effectively tuned from green (similar to 2.4 eV) to violet (similar to 2.8 eV) using a single-step synthesis process that is based on modulating the arrival pattern of film forming species with sub-monolayer resolution, while keeping the amount of Ag in the films constant. Our data indicate that the optical response of the films is the result of LSPRs on isolated Ag nanoparticles that are seemingly shifted by dipolar interactions between neighboring particles. The synthesis strategy presented may be of relevance for enabling integration of plasmonic nanocomposite films on thermally sensitive substrates. Published by AIP Publishing.
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| 29. |
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| 30. |
- Mishra, K., et al.
(författare)
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Ultrafast Demagnetization Control in Magnetophotonic Surface Crystals
- 2022
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 22:23, s. 9773-80
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic memory combining plasmonics and magnetism is poised to dramatically increase the bit density and energy efficiency of light-assisted ultrafast magnetic storage, thanks to nanoplasmon-driven enhancement and confinement of light. Here we devise a new path for that, simultaneously enabling light driven bit downscaling, reduction of the required energy for magnetic memory writing, and a subtle control over the degree of demagnetization in a magnetophotonic surface crystal. It features a regular array of truncated-nanocone-shaped Au-TbCo antennas showing both localized plasmon and surface lattice resonance modes. The ultrafast magnetization dynamics of the nanoantennas show a 3-fold resonant enhancement of the demagnetization efficiency. The degree of demagnetization is further tuned by activating surface lattice modes. This reveals a platform where ultrafast demagnetization is localized at the nanoscale and its extent can be controlled at will, rendering it multistate and potentially opening up so-far-unforeseen nanomagnetic neuromorphic-like systems operating at femtosecond time scales controlled by light.
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| 31. |
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| 32. |
- Mishra, K., et al.
(författare)
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Ultrafast demagnetization in a ferrimagnet under electromagnetic field funneling
- 2021
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 13:46, s. 19367-19375
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Tidskriftsartikel (refereegranskat)abstract
- The quest to improve the density, speed and energy efficiency of magnetic memory storage has led to the exploration of new ways of optically manipulating magnetism at the ultrafast time scale, in particular in ferrimagnetic alloys. While all-optical magnetization switching is well-established on the femtosecond timescale, lateral nanoscale confinement and thus the potential significant reduction of the size of the magnetic element remains an outstanding challenge. Here we employ resonant electromagnetic energy funneling through plasmon nanoantennas to influence the demagnetization dynamics of a ferrimagnetic TbCo alloy thin film. We demonstrate how Ag nanoring-shaped antennas under resonant optical femtosecond pumping reduce the overall demagnetization in the underlying films up to three times compared to non-resonant illumination. We attribute such a substantial reduction to the nanoscale confinement of the demagnetization process. This is qualitatively supported by the electromagnetic simulations that strongly evidence the resonant optical energy-funneling to the nanoscale from the nanoantennas into the ferrimagnetic film. This observation is an important step for reaching deterministic ultrafast all-optical magnetization switching at the nanoscale in such systems, opening a route to develop nanoscale ultrafast magneto-optics.
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| 33. |
- Mottamchetty, Venkatesh, et al.
(författare)
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Terahertz emission from epitaxial α-W/Co60Fe40 spintronic emitters
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report efficient terahertz (THz) generation in epitaxial α-W/Co60Fe40 spintronic emitters. Two types of emitters have been investigated; epitaxial α-W(110)/Co60Fe40(110) and α-W(001)/Co60Fe40(001) deposited on single crystalline Al2O3(11-20) and MgO(001) substrates, respectively. The generated THz radiation is about 10% larger for α-W(110)/Co60Fe40(110) grown on single crystalline Al2O3(11-20), which is explained by the fact that the α-W(110)/Co60Fe40(110) interface for this emitter is more transparent to the spin current due to the presence of Ångström-scale interface intermixing at the W/CoFe interface. Our results also reveal that the generation of THz radiation is larger when pumping with the laser light from the substrate side, which is explained by a larger part of the laser light due to interference effects in the film stack being absorbed in the ferromagnetic Co60Fe40 layer in this measurement configuration.
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| 34. |
- Nisoli, Cristiano, et al.
(författare)
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Deliberate exotic magnetism via frustration and topology
- 2017
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Ingår i: Nature Physics. - : NATURE PUBLISHING GROUP. - 1745-2473 .- 1745-2481. ; 13:3, s. 200-203
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Tidskriftsartikel (refereegranskat)abstract
- Introduced originally to mimic the unusual, frustrated behaviour of spin ice pyrochlores, artificial spin ice can be realized in odd, dedicated geometries that open the door to new manifestations of a higher level of frustration.
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| 35. |
- Nouhi, Shirin, et al.
(författare)
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Distortion of surfactant lamellar phases induced by surface roughness
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembly is a characteristic property of soft matter and understanding the factors which assist or perturb this process is of a great importance in many biological and industrial processes. Amphiphiles self-assemble and order into a variety of structures including well-ordered lamellar phases. The present work uses neutron reflectometry to explore the effects of both interface roughness and temperature on the lamellar-phase structure of a non-ionic surfactant at a solid/liquid interface. The structure of concentrated solutions of tetraethyleneglycol dodecyl ether has been compared against a smooth surface and one with a roughness of the order of the lamellar spacing. The results showed that the surfactant forms a well-order and aligned structure at smooth surface that extends to a depth of micrometers from the interface. Increasing the temperature of the sample and subsequent cooling helped the alignment and increased the number of oriented layers at the surface. The same sample formed a significantly less aligned structure at a rough surface that did not align to same extent after heating. The perturbation of the structure caused by thermal fluctuations was found to be much less than that imposed by a small surface roughness. Keywords
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| 36. |
- Nouhi, Shirin, et al.
(författare)
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Distortion of surfactant lamellar phases induced by surface roughness star
- 2020
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Ingår i: The European Physical Journal Special Topics. - : SPRINGER HEIDELBERG. - 1951-6355 .- 1951-6401. ; 229:17-18, s. 2807-2823
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembly is a characteristic property of soft matter. Understanding the factors which assist or perturb this process is of great importance in many biological and industrial processes. Amphiphiles self-assemble and order into a variety of structures including well-ordered lamellar phases. The present work uses neutron reflectometry and neutron scattering to explore the effects of both interface roughness and temperature on the lamellar-phase structure of a non-ionic surfactant at a solid/liquid interface. The structure of concentrated solutions of tetraethyleneglycol dodecyl ether has been compared against a smooth surface and one with a roughness of the order of the lamellar spacing. This has been done in order to investigate the role perturbations have on the overall lamellar order, when these have length scales of the order of the interactions between neighboring lamellae. The results showed that the surfactant forms a well-ordered and aligned structure at a smooth surface, extending to a depth of several micrometers from the interface. Increasing the temperature of the sample and subsequent cooling promotes alignment and increases the number of oriented layers at the surface. The same sample forms a significantly less aligned structure against a rough surface that does not align to the same extent, even after heating. The perturbation of the structure caused by thermal fluctuations was found to be much less than that imposed by a small surface roughness.
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| 37. |
- Nouhi, Shirin, et al.
(författare)
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Grazing-Incidence Small Angle Neutron Scattering from Structures below an Interface
- 2017
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 50:4, s. 1066-1074
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Tidskriftsartikel (refereegranskat)abstract
- Changes of scattering are observed as the grazing angle of incidence of an incoming beam increases and probes different depths in samples. A model has been developed to describe the observed intensity in grazing incidence small angle neutron scattering (GISANS) experiments. This includes the significant effects of instrument resolution, the sample transmission, which depends on both absorption and scattering, as well as the sample structure. The calculations are tested with self-organised structures of two colloidal samples with different size particles that were measured on two different instruments. The model allows calculations for various instruments with defined resolution and can be used to design future improved experiments. The possibilities and limits of GISANS for different studies are discussed using the model calculations.
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| 38. |
- Novoselova, Iuliia P., et al.
(författare)
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Large uniaxial magnetostriction with sign inversion at the first order phase transition in the nanolaminated Mn2GaC MAX phase
- 2018
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Ingår i: Scientific Reports. - London : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- In 2013, a new class of inherently nanolaminated magnetic materials, the so called magnetic MAX phases, was discovered. Following predictive material stability calculations, the hexagonal Mn2GaC compound was synthesized as hetero-epitaxial films containing Mn as the exclusive M-element. Recent theoretical and experimental studies suggested a high magnetic ordering temperature and non-collinear antiferromagnetic (AFM) spin states as a result of competitive ferromagnetic and antiferromagnetic exchange interactions. In order to assess the potential for practical applications of Mn2GaC, we have studied the temperature-dependent magnetization, and the magnetoresistive, magnetostrictive as well as magnetocaloric properties of the compound. The material exhibits two magnetic phase transitions. The Neel temperature is T-N similar to 507 K, at which the system changes from a collinear AFM state to the paramagnetic state. At T-t = 214 K the material undergoes a first order magnetic phase transition from AFM at higher temperature to a non-collinear AFM spin structure. Both states show large uniaxial c-axis magnetostriction of 450 ppm. Remarkably, the magnetostriction changes sign, being compressive (negative) above T-t and tensile (positive) below the T-t. The sign change of the magnetostriction is accompanied by a sign change in the magnetoresistance indicating a coupling among the spin, lattice and electrical transport properties.
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| 39. |
- Oppeneer, Peter M., et al.
(författare)
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Plasmonic lasers turn magnetic
- 2022
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Ingår i: Nature Photonics. - : Springer Nature. - 1749-4885 .- 1749-4893. ; 16:1, s. 11-13
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 40. |
- Papaioannou, Evangelos Th, et al.
(författare)
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Dimensionality and confinement effects in delta-doped Pd(Fe) layers
- 2010
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 22:23, s. 236004-
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Tidskriftsartikel (refereegranskat)abstract
- We address the dimensionality aspects of the magnetic ordering in delta-doped Pd(Fe) structures. The key property we investigate, via magneto-optic Kerr measurements, is the magnetization induced by iron in palladium, over a wide temperature range 5 K < T < 300 K. The dimensional crossover we observe cannot be rationalized on the basis of structural considerations alone, since we find the dimensionality of the low temperature and of the critical region can differ. We discuss the crossover in terms of the temperature dependence of the magnon modes, giving rise to lower dimensionality at low temperatures.
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| 41. |
- Pappas, S. D., et al.
(författare)
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A Cost-Effective Growth of SiOx Thin Films by Reactive Sputtering : Photoluminescence Tuning
- 2011
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 11:4, s. 3684-3687
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Tidskriftsartikel (refereegranskat)abstract
- We present a new cost-effective method to produce substoichiometric SiO2 thin films by means of a simple sputter-coater operated at a base pressure of 1 x 10(-3) mbar. During sputtering air is introduced through a fine valve so that the sputtering gas is a mixture of air/Ar. High-resolution electron microscopy shows the formation of amorphous SiOx thin films for the as-deposited samples. The index x approaches 1 when the ratio of the partial pressure of air/Ar tends to 0.1. On the other hand, pure silica is formed when the ratio of the partial pressure of air/Ar approaches 0.5. The films in the as-deposited state show intense green yellow photoluminescence. This fades away with short annealing under air at 950 degrees C. If on the other hand, prolonged annealing is performed under Argon atmosphere at 1000 degrees C, red-infrared photoluminescence is recorded due to the formation of Si nanocrystals embedded in SiO2. This simple method could be suitable for the production of thin SiOx films with embedded nanocrystals for optoelectronic or photovoltaic applications.
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| 42. |
- Pohlit, Merlin, et al.
(författare)
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Collective magnetic dynamics in artificial spin ice probed by ac susceptibility
- 2020
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 101:13
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Tidskriftsartikel (refereegranskat)abstract
- We report on the study of the thermal dynamics of square artificial spin ice, probed by means of temperatureand frequency-dependent ac susceptibility. Pronounced influence of the interisland coupling strength was found on the frequency response of the samples. Through the subsequent analysis of the frequency- and coupling-dependent freezing temperatures, we discuss the phenomenological parameters obtained in the framework of the Vogel-Fulcher-Tammann law in terms of the samples' microscopic features. The high sensitivity and robust signal to noise ratio of ac susceptibility validate the latter as a promising and simple experimental technique for resolving the dynamics and temperature driven dynamics crossovers for the case of artificial spin ice.
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| 43. |
- Poulopoulos, Panagiotis, et al.
(författare)
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Intense Quantum Confinement Effects in Cu(2)O Thin Films
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:30, s. 14839-14843
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Tidskriftsartikel (refereegranskat)abstract
- Thin Cu(2)O films in the thickness range 0.75-230 nm have been prepared on high-quality corning glass, quartz, and Si(100) substrates by radio frequency magnetron sputtering of Cu targets and subsequent oxidation in a furnace under air. Ultraviolet-visible light absorption spectroscopy experiments reveal a blue shift of the energy between the top valence and the first excited conduction sub-bands. The shift increases smoothly as the film thickness decreases. The maximum value observed for the thinnest film is very large, reaching a value of 1.2 eV. Such a shift was not easy to be observed in the past due to the very small Bohr radius of Cu(2)O. The experimental results, which indicate the presence of intense quantum confinement effects, are well-described by theoretical calculations based on the potential morphing method in the Hartree-Fock approximation.
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| 44. |
- Ravensburg, Anna Lena, 1994-, et al.
(författare)
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Boundary-induced phase in epitaxial iron layers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report the discovery of a boundary-induced body-centered tetragonal (bct) iron phase in thin films deposited on MgAl2O4 (001) substrates. We present evidence for this phase using detailed x-ray analysis and ab-initio density functional theory calculations. A lower magnetic moment and a rotation of the easy magnetisation direction are observed, as compared to body-centered cubic (bcc) iron. Our findings expand the range of known crystal and magnetic phases of iron, providing valuable insights for the development of heterostructure devices using ultra-thin iron layers.
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| 45. |
- Ravensburg, Anna L., et al.
(författare)
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Effect of iron layer thickness on the interlayer exchange coupling in Fe/MgO (001) superlattices
- 2024
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:22
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Tidskriftsartikel (refereegranskat)abstract
- We describe the effect of the Fe layer thickness on the antiferromagnetic interlayer exchange coupling in [Fe/MgO]? superlattices. An increase in coupling strength with increasing Fe layer thickness is observed, which highlights the need for including the extension of both layers when discussing the interlayer exchange coupling in superlattices.
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| 46. |
- Ravensburg, Anna L., et al.
(författare)
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Epitaxy enhancement in oxide/tungsten heterostructures by harnessing the interface adhesion
- 2024
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Ingår i: Applied Physics A. - : Springer. - 0947-8396 .- 1432-0630. ; 130:2
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Tidskriftsartikel (refereegranskat)abstract
- The conditions whereby epitaxy is achieved are commonly believed to be mostly governed by misfit strain. We report on a systematic investigation of growth and interface structure of single crystalline tungsten thin films on two different metal oxide substrates, Al2O3 (11 (2) over bar0) and MgO (001). We demonstrate that despite a significant mismatch, enhanced crystal quality is observed for tungsten grown on the sapphire substrates. This is promoted by stronger adhesion and chemical bonding with sapphire compared to magnesium oxide, along with the restructuring of the tungsten layers close to the interface. The latter is supported by ab initio calculations using density functional theory. Finally, we demonstrate the growth of magnetic heterostructures consisting of high-quality tungsten layers in combination with ferromagnetic CoFe layers, which are relevant for spintronic applications.
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| 47. |
- Ravensburg, Anna Lena, 1994-, et al.
(författare)
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GENL: An extensible fitting program for Laue oscillations
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- GENL is a flexible program that can be used to simulate and/or fit x-ray diffraction data from epitaxial thin films exhibiting Laue oscillations. It utilizes differential evolution within a genetic algorithm for the fitting of data and is based on the kinematic theory of diffraction. Effects of polarization, absorption, the Lorentz factor, as well as instrumental resolution and vibrations are taken into account. Useful parameters that can be extracted after fitting include: atomic interplanar spacings, number of coherently scattering atomic planes, strain profiles along the film thickness, and crystal roughness. The program has been developed in MATLAB and employs a graphical user interface. The deployment strategy is twofold whereby the software can either be obtained in source code form and executed within the MATLAB environment, or as a pre-compiled binary for those who prefer not to run it within MATLAB. Finally, GENL can easily be extended to simulate multilayered film systems, superlattices, and films with atomic steps. The program is released under the GNU General Public Licence.
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| 48. |
- Ravensburg, Anna Lena
(författare)
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Growth of high quality Fe thin films : A study of the effect of mismatch strain on the physical properties of Fe
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work in this licentiate is devoted to investigating the epitaxial growth of thin Fe layers on MgAl2O4 (001) and MgO (001) substrates using dc magnetron sputtering. The aim is to qualitatively and quantitatively determine the crystal quality of the grown Fe layers depending on their thickness, substrate material, and selected deposition parameters. The effect of the crystal quality on the magnetic and electronic transport properties is discussed. The structural characterization of the epitaxial Fe thin films is carried out by x-ray reflectometry and diffraction as well as transmission electron microscopy. X-ray scattering measurements and analysis with related models allow for a quantitative determination of layering, crystal quality, and strain profiles in the growing Fe. Magnetic properties are determined using a combination of longitudinal magneto-optical Kerr effect measurements, Kerr microscopy, and scanning electron microscopy with polarization analyser. Electronic transport properties are characterized by four-point probe measurements of the thin films. The epitaxial growth of Fe is found to be highly substrate dependent: Fe layers grown on MgAl2O4 have a significantly higher crystal quality, as compared to Fe grown on MgO. The difference in crystal quality is attributed to different strain states in Fe, which is supported by theoretical calculations of the critical thickness on both substrates. Moreover, an anomalous elastic response in Fe at the thin film limit is found. The magnetic properties of Fe are weakly reflecting the differences in crystal quality of the Fe layers. However, the difference in crystal quality affects the electronic transport properties. The results of this study on epitaxial Fe layers can provide insights into strain and defect engineering in Fe thin films, which can additionally serve as model systems for finite size effects.
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| 49. |
- Ravensburg, Anna L., et al.
(författare)
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Influence of misfit strain on the physical properties of Fe thin films
- 2022
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 761
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the growth of thin Fe layers on MgAl2O4 (001) and MgO (001) substrates using dc magnetron sputtering. The crystal quality of Fe layers deposited on MgAl2O4 is found to be substantially higher as compared to Fe grown on MgO substrates. The effects of the crystal quality on the magnetic and electric transport properties are discussed.
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| 50. |
- Ravensburg, Anna L.
(författare)
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Order and interfaces in epitaxial heterostructures : Structure and magnetism
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work in this dissertation is devoted to investigating order and interfaces in epitaxial heterostructures. To achieve that the software tool box GenL was developed for simulating and fitting x-ray diffraction patterns from epitaxial thin films, which is used to access structural information on the length scales of interfaces and atomic bonds. Employing GenL, it is shown that a small lattice mismatch between substrate and epitaxial layer is not the sole origin of high crystal quality, as demonstrated for nearly strain-free epitaxial growth of tungsten on sapphire with a lattice mismatch of up to 19.4 %. Furthermore, it is discussed that electronic states at the substrate/film interface can have substantial significance for the crystal structure of an epitaxial layer. For instance, despite a nearly mismatch-free interface of body-centered cubic iron on spinel, the presence of a boundary-induced interface layer with tetragonally distorted crystal structure is discovered, which has a profound impact on the magnetic properties. Finally, when creating multilayered structures, not only the interface states but the total structure is found to influence the physical properties, which is demonstrated for the interlayer exchange coupling in [Fe/MgO]Nsuperlattices.Note: This PhD thesis is partly based on the licentiate dissertation "Growth of high quality Fe thin films" by Anna L. Ravensburg, Uppsala University, 2022. Particularly parts of: Chapter 1, Sections 2.0, 2.1, 2.2, 3.0, 3.1, 3.2, 3.3, 5.1, and Fig. 2.6 are adapted from the licentiate thesis with minor edits and updates.
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