| 1. |
- Arnalds, Unnar B., 1976-
(author)
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Magnetic Order in Artificial Structures
- 2012
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Doctoral thesis (other academic/artistic)abstract
- The topic of this thesis is the investigation of the magnetic properties of artificially created magnetic structures. Applying different characterization techniques, ranging from direct imaging methods to reciprocal space techniques, the properties of lithographically patterned arrays of magnetic thin film and multilayer elements are investigated by exploring their magnetic state, extending from the atomic scale up to collective ordering phenomena of nano-magnetic elements.Laterally patterned amorphous multilayer arrays of combined circular and ellipsoidal islands were investigated. The arrays contain a variety of length scales, ranging from their nanometer scale multilayer structure to their lateral periodicity in the micrometer range. The attributes of these arrays are explored using different techniques, applicable for addressing the magnetization at different length scales, including magneto-optical techniques, micromagnetic simulations and x-ray resonant magnetic scattering.Arrays of dipole interacting elongated magnetic elements composed of Pd(Fe) thin films were investigated. Pd(Fe) films have a low Curie temperature which can be tuned by the thickness of the Fe layer embedded in Pd. By this, the interaction and the shape anisotropy energies can be brought down to energy scales comparable to room temperature enabling the possibility of investigating the effect of thermal excitations on such arrays. The temperature dependent magnetization of an artificial square spin ice array was investigated by magneto-optical measurements demonstrating the possibility of observing an order-disorder transition in an artificial square spin ice system. The role of dipolar interactions and the possibility of achieving thermal ground state ordering was then further investigated by magnetically sensitive photoemission electron microscopy imaging of ring arrangements of elongated Pd(Fe) elements. The results reveal a high probability of achieving a thermal ground state ordering of the magnetization of the islands.
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| 2. |
- Arnalds, Unnar B., et al.
(author)
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Thermal transitions in nano-patterned XY-magnets
- 2014
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:4, s. 042409-
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Journal article (peer-reviewed)abstract
- We have fabricated ultra-thin disc shaped islands wherein shape anisotropy confines the moment to the island plane, creating XY-like superspins. At low temperatures, the superspins are blocked, and, as the temperature is increased, they undergo a transition into a superparamagnetic state. The onset of this dynamic superspin state scales with the diameter of the islands, and it persists up to a temperature governed by the intrinsic ordering temperature of the island material defining a range in temperature in which dynamic behavior of the magnetic islands can be obtained.
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| 3. |
- Arnalds, Unnar, et al.
(author)
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Thermalized ground state of artificial kagome spin ice building blocks
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:11, s. 112404-
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Journal article (other academic/artistic)abstract
- We present a direct magnetic imaging study on the thermal macrospin ordering of artificial kagome spin ice building blocks. Using photoemission electron microscopy, employing x-ray magnetic circular dichroism, we are able to resolve the single domain magnetic nature of the macrospins and determine the states of the combined building block structures. The nano-patterning and material selection allows thermally activated magnetization reversal for the macrospins to occur. The ordering of the macrospins is dominated by the ground state, consistent with a thermal ground state ordering. This work paves the way for the realization of extended artificial spin ice structures exhibiting experimentally accessible thermal behavior
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| 4. |
- Bran, Cristina, et al.
(author)
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Magnetic Properties of Fe/WRe (001) Multilayers
- 2014
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In: Journal of Surfaces and Interfaces of Materials. - : American Scientific Publishers. - 2164-7542. ; 2:1, s. 33-39
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Journal article (peer-reviewed)abstract
- Following recent theoretical predictions on perpendicular uniaxial magnetocrystalline anisotropy in multilayers of 5 monolayers of Fe and 2 monolayers of W x Re100–x with tetragonally strained components, we have measured the magnetization and detailed atomic structure in a series of such samples with x = 20–80 at%. Although the achieved strain in the WRe layers is smaller than in the modelled case, we do observe a positive uniaxial magnetocrystalline anisotropy of around 0.6 MJ/m3 at 40 K, after accounting for the in-plane shape anisotropy. This causes the out-of-plane saturation field to be reduced considerably compared to a pure Fe thin film, while the saturation magnetization is maintained at a value which is enhanced by at least 30% from what would be expected from the multilayer composition alone. The coercivity is low, on the order of 6 kA/m in all samples.
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| 5. |
- Delimitis, Andreas, et al.
(author)
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Microstructural Investigation of SiOx Thin Films Grown by Reactive Sputtering on (001) Si Substrates
- 2012
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In: Journal of Nano Research. - 1661-9897. ; 17, s. 147-156
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Journal article (peer-reviewed)abstract
- In the Current Study, the Structural Characteristics of Siox Thin Films Grown by Magnetron Sputtering on Si Substrates Are Reported. High Resolution Transmission Electron Microscopy Revealed the Formation of Amorphous Siox Films for the as-Deposited Samples, as Well as the Ones Annealed in Ambient Air for 30 Min at 950oC and of Si Nanocrystals, Embedded in Amorphous Siox, after Ar Annealing for 1-4 Hours at 1000oC. the Nanocrystals, with Sizes up to 6 Nm, Predominately Exhibit {111} Lattice Planes. Energy-Dispersive X-Ray Analysis Showed that the Si/O Ratio Is between 0.5-1, I.e. the Amorphous Films Comprise of a Mixture of Sio2 and Sio. Phase Images and Corresponding Strain Maps Created Using Fourier Filtering Revealed a Uniform Contrast in the Nanocrystals, which Shows that the Si Lattice Constant Does Not Vary Significantly. the Residual Strain Variations, around 4%, May Account for the Possible Existence of a Small Percentage of Highly Disordered Si or Siox Residual Clusters inside the Regular Si Matrix, in Full Agreement with Photoluminescence Measurements Performed on the same Materials.
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| 6. |
- Hase, Thomas P. A., et al.
(author)
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Proximity effects on dimensionality and magnetic ordering in Pd/Fe/Pd trialyers
- 2014
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:10, s. 104403-
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Journal article (peer-reviewed)abstract
- The element-specific magnetization and ordering in trilayers consisting of 0.3-1.4 monolayer (ML) thick Fe layers embedded in Pd(001) has been determined using x-ray resonant magnetic scattering. The proximity to Fe induces a large moment in the Pd which extends similar to 2 nm from the interfaces. The magnetization as a function of temperature is found to differ significantly for the Fe and Pd sublattices: The Pd signal resembles the results obtained by magneto-optical techniques with an apparent three-dimensional (3D) to two-dimensional (2D) transition in spatial dimensionality for Fe thickness below similar to 1 ML. In stark contrast, the Fe data exhibits a 2D behavior. No ferromagnetic signal is obtained from Fe below the 2D percolation limit in Fe coverage (similar to 0.7 ML), while Pd shows a ferromagnetic response for all samples. The results are attributed to the temperature dependence of the susceptibility of Pd and a profound local anisotropy of submonolayered Fe.
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| 7. |
- Hellsing, Maja S., et al.
(author)
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Crystalline order of polymer nanoparticles over large areas at solid/liquid interfaces
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:22, s. 221601-
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Journal article (peer-reviewed)abstract
- We report on the formation of large two-dimensional domains (about 20 cm2) of oriented and ordered structures of polystyrene particles dispersed in water at a solid/liquid interface. Gentle flow of the dispersed sample into the holder at a shear strain rate of about 0.1 s−1 caused particles at the air/latex meniscus to self-assemble in a regular structure on both solid silica or alumina surfaces. Scattering experiments show that the particle separation at the surface was the same as in the bulk and determined by repulsion arising from the charges on the particles. Close-packed planes formed parallel to the interface.
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| 8. |
- Hostert, C, et al.
(author)
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Ab-initio molecular dynamics model for density, elastic properties and short range order of Co-Fe-Ta-B metallic glass thin films
- 2011
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23:47, s. 475401-
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Journal article (peer-reviewed)abstract
- Density, elastic modulus and the pair distribution function of Co-Fe-Ta-B metallic glasses were obtained by ab-initio molecular dynamics simulations and measured for sputtered thin films using X-ray reflectivity, nanoindentation and X-ray diffraction using high energy photons. The computationally obtained density of 8.19 g/cm3 for Co43Fe20Ta5.5B31.5 and 8.42 g/cm3 for Co45.5Fe24Ta6B24.5, as well as the Young’s moduli of 273 and 251 GPa, respectively, are consistent with our experiments and literature data. These data, together with the good agreement between the theoretical and the experimental pair distribution functions, indicate that the here established model is useful to describe density, elasticity and short range order of Co-Fe-Ta-B metallic glass thin films. Irrespective of the investigated variation in chemical composition, (Co,Fe)-B cluster formation and Co-Fe interactions are identified by density of states analysis. Strong bonds within the structural units and between the metallic species may give rise to the comparatively large stiffness.
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| 9. |
- Hostert, Carolin, et al.
(author)
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Density, elastic and magnetic properties of Co–Fe–Ta–Si metallic glasses by theory and experiment
- 2012
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In: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456.
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Journal article (peer-reviewed)abstract
- Ab initio molecular dynamics simulations were employed to study the density, elastic and magnetic properties of Co–Fe–Ta–Si10 metallic glass thin films. A density of 8.03 g cm3, a Young’s modulus of 187 GPa and a volume magnetization of 0.089 lBA ˚ 3 werecalculated and validated by thin film experiments. The extensive stiffness of this glass may be related to the existence of strong(Fe,Co)–Si clusters as revealed by ab initio chemical short-range order data.
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| 10. |
- Jayathilaka, K. M. D. C., et al.
(author)
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Ammonium Sulfide Surface Treatment of Electrodeposited p-Type Cuprous Oxide Thin Films
- 2014
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In: Electronic Materials Letters. - : Springer Science and Business Media LLC. - 1738-8090 .- 2093-6788. ; 10:2, s. 379-382
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Journal article (peer-reviewed)abstract
- The effects of ammonium sulfide surface treatment on electrodeposited p-type polycrystalline cuprous oxide (Cu2O) thin films deposited on Ti substrates were studied. The structural and morphological properties of the films were investigated using scanning electron microscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy. The changes in the conductivities and photocurrents of the films after the ammonium sulfide treatment were determined Films that had undergone the ammonium sulfide treatment showed reduced resistivities, enhanced spectral photoresponses, and enhanced current-voltage characteristics. The results showed that ammonium sulfide treatment improved the peak output current of the p-type Cu2O films by about 400% compared with those of bare Cu2O films. This improvement is attributed to the passivation of defects in the films by sulfur, showing that sulfur passivation provides a good method for improving of Cu2O-based devices.
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