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- Baldi, A., et al.
(författare)
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Mg/Ti multilayers : Structural and hydrogen absorption properties
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:22, s. 224203-
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Tidskriftsartikel (refereegranskat)abstract
- Mg-Ti alloys have uncommon optical and hydrogen absorbing properties, originating from a "spinodal-like" microstructure with a small degree of chemical short-range order in the atomic distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities. Notwithstanding the large lattice mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. On exposure to H-2 gas a two-step hydrogenation process occurs with the Ti layers forming the hydride before Mg. From in situ measurements of the bilayer thickness Lambda at different hydrogen pressures, we observe large out-of-plane expansions of Mg and Ti layers on hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. On unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces.
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| 2. |
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| 3. |
- Melander, Emil, et al.
(författare)
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Influence of the magnetic field on the plasmonic properties of transparent Ni anti-dot arrays
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:6, s. 063107-
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Tidskriftsartikel (refereegranskat)abstract
- Extraordinary optical transmission is observed due to the excitation of surface plasmon polaritons in 2-dimensional hexagonal anti-dot patterns of pure Ni thin films, grown on sapphire substrates. A strong enhancement of the polar Kerr rotation is recorded at the surface plasmon related transmission maximum. Angular resolved reflectivity measurements under an applied field reveal an enhancement and a shift of the normalized reflectivity difference upon reversal of the magnetic saturation (transverse magneto-optical Kerr effect-TMOKE). The change of the TMOKE signal clearly shows the magnetic field modulation of the dispersion relation of SPPs launched in a 2D patterned ferromagnetic Ni film. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742931]
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| 4. |
- Qviller, A. J., et al.
(författare)
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Direct observation of magnetic proximity effects in amorphous exchange-spring magnets by neutron reflectometry
- 2020
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Ingår i: Physical Review Materials. - 2475-9953. ; 4:10
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report a direct observation of a magnetic proximity effect in an amorphous thin-film exchange-spring magnet by the use of neutron reflectometry. The exchange-spring magnet is a trilayer consisting of two ferromagnetic layers with high T-c separated by a ferromagnetic layer, which is engineered to have a significantly lower T-c than the embedding layers. This enables us to measure magnetization depth profiles at which the low-T-c material is in a ferromagnetic or paramagnetic state, while the embedding layers are ferromagnetic. A clear proximity effect is observed 7 K above the intrinsic T-c of the embedded layer, with a range extending 50 angstrom.
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| 7. |
- Andreasson, Jakob, et al.
(författare)
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Saturated ablation in metal hydrides and acceleration of protons and deuterons to keV energies with a soft-x-ray laser
- 2011
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 83:1, s. 016403-
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Tidskriftsartikel (refereegranskat)abstract
- Studies of materials under extreme conditions have relevance to a broad area of research, including planetary physics, fusion research, materials science, and structural biology with x-ray lasers. We study such extreme conditions and experimentally probe the interaction between ultrashort soft x-ray pulses and solid targets (metals and their deuterides) at the FLASH free-electron laser where power densities exceeding 1017 W/cm2 were reached. Time-of-flight ion spectrometry and crater analysis were used to characterize the interaction. The results show the onset of saturation in the ablation process at power densities above 1016 W/cm2. This effect can be linked to a transiently induced x-ray transparency in the solid by the femtosecond x-ray pulse at high power densities. The measured kinetic energies of protons and deuterons ejected from the surface reach several keV and concur with predictions from plasma-expansion models. Simulations of the interactions were performed with a nonlocal thermodynamic equilibrium code with radiation transfer. These calculations return critical depths similar to the observed crater depths and capture the transient surface transparency at higher power densities.
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| 8. |
- Arnalds, Unnar B., et al.
(författare)
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A new look on the two-dimensional Ising model : thermal artificial spins
- 2016
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18
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Tidskriftsartikel (refereegranskat)abstract
- We present a direct experimental investigation of the thermal ordering in an artificial analogue of an asymmetric two-dimensional Ising system composed of a rectangular array of nano-fabricated magnetostatically interacting islands. During fabrication and below a critical thickness of the magnetic material the islands are thermally fluctuating and thus the system is able to explore its phase space. Above the critical thickness the islands freeze-in resulting in an arrested thermalized state for the array. Determining the magnetic state we demonstrate a genuine artificial two-dimensional Ising system which can be analyzed in the context of nearest neighbor interactions.
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| 9. |
- Arnalds, Unnar B., 1976-
(författare)
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Magnetic Order in Artificial Structures
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 10. |
- Arnalds, Unnar B., et al.
(författare)
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Magnetic structure and diffracted magneto-optics of patterned amorphous multilayers
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:14, s. 144434-1-144434-8
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Tidskriftsartikel (refereegranskat)abstract
- We present magneto-optical Kerr effect measurements of patterned arrays of Co68Fe24Zr8 / Al2O3 amorphous multilayers. The multilayers were patterned in two dimensions into two different arrangements of circular and ellipsoidal islands. Magnetization loops were recorded in a longitudinal geometry using both the specularly reflected beam as well as diffracted beams scattered off the patterned films. The magnetization of the patterned structures is significantly different from the magnetization of a continuous multilayer owing to the lateral confinement of the pattern and the introduction of additional dipolar coupling between the layers at the edges of the islands. By investigating the magnetic response at the different diffraction orders from the two different configurations of islands we are able to observe the magnetization at different length scales and determine the magnetic response of the circular and ellipsoidal islands individually.
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