| 1. |
- Baldi, A., et al.
(author)
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Mg/Ti multilayers : Structural and hydrogen absorption properties
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:22, s. 224203-
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Journal article (peer-reviewed)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.
(author)
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Influence of the magnetic field on the plasmonic properties of transparent Ni anti-dot arrays
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:6, s. 063107-
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Journal article (peer-reviewed)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.
(author)
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Direct observation of magnetic proximity effects in amorphous exchange-spring magnets by neutron reflectometry
- 2020
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In: Physical Review Materials. - 2475-9953. ; 4:10
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Journal article (peer-reviewed)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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| 5. |
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| 6. |
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| 7. |
- Andreasson, Jakob, et al.
(author)
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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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In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 83:1, s. 016403-
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Journal article (peer-reviewed)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.
(author)
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A new look on the two-dimensional Ising model : thermal artificial spins
- 2016
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18
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Journal article (peer-reviewed)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-
(author)
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Magnetic Order in Artificial Structures
- 2012
-
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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| 10. |
- Arnalds, Unnar B., et al.
(author)
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Magnetic structure and diffracted magneto-optics of patterned amorphous multilayers
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:14, s. 144434-1-144434-8
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Journal article (peer-reviewed)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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| 11. |
- 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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| 12. |
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| 13. |
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| 14. |
- Bloch, J., et al.
(author)
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Hydrogen-vanadium system in thin films : Effect of film thickness
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:24, s. 245428-
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Journal article (peer-reviewed)abstract
- The absorption of hydrogen in thin V(001) films under pressures of 1-10(5) Pa H-2 and at temperatures between 350 and 530 K was studied as a function of film thickness between 50 and 5 nm using in situ electrical resistivity measurements. The critical temperatures for the order-disorder transitions taking place in the V-H system are decreased with decreasing film thickness. At 370 K, the high-concentration (epsilon-VH) phase disappears as the thickness of the film is reduced from 50 to 10 nm and the low-concentration (beta-V2H) phase follows when the film thickness is further decreased to 5 nm. The difference in solubility at 530 K of H in the alpha phase of V films down to 10 nm is small but it increases for lower temperatures. At low concentrations the heat of solution in the 10 nm film is somewhat lower than in the bulk, but around H/V = 0.07, the values of Delta H-H in the film approach those of the bulk. The values of Delta S-H(nc) of the film are rather close to those of the bulk. Significant difference is found in the pressure-resistivity isotherms above the maximum of the residual resistivity, Delta R-max. For the 10 nm film, in contrast to the 50 nm film, a minimum is located just beyond Delta R-max for the whole temperature range but the difference between the maximum and minimum starts to decrease above 420 K. This results in, by extrapolation, the vanishing of the maximum around 520 K. We suggest that this phenomenon is the result of an Oz -> T transition due to a final size effect. This transition means additional randomly distributed interstitial sites available for the H atoms in the lattice of the V film leading to a continuous increase in the residual resistivity with H concentration.
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| 15. |
- Bloch, J., et al.
(author)
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Prediction and Hydrogen Acceleration of Ordering in Iron-Vanadium Alloys
- 2012
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:21, s. 215503-
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Journal article (peer-reviewed)abstract
- Ab initio calculations of binary metallic systems often predict ordered compounds in contrast to empirical reports of solid solutions or disordered phases. These discrepancies are usually attributed to slow kinetics that retains metastable structures at low temperatures. The Fe-V system is an example of this phenomenon, in which we predict two ordered stable ground states, Fe3V and FeV3, whereas a disordered sigma phase is reported. We propose to overcome this difficulty by hydrogen absorption, which facilitates metal atom mobility through vacancy formation and separation between the two elements due to their opposite affinities towards it, thus accelerating transformation kinetics. Hydrogen also increases the relative stability of the ordered structures compared with that of the sigma phase without affecting the shape of the phase diagram. The hydrogen-induced formation of the ordered structures is expressed by a reversible decrease of the electrical resistivity with increasing hydrogen pressure. Such behavior has not been reported before in thin H absorbing films. Formation of the ordered structures is further substantiated by the kinetics of the resistivity changes upon variation of the hydrogen pressure, where two stages are distinguished: a fast initial stage and a much slower subsequent process in which the resistivity changes direction, associated with hydrogen dissolution and phase transformation, respectively.
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| 16. |
- Brucas, R., et al.
(author)
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Magnetic anisotropy and evolution of ground-state domain structures in bcc Fe81Ni19/Co(001) superlattices
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - : The American Physical Society. - 1098-0121 .- 1550-235X. ; 78:2, s. 024421-
-
Journal article (peer-reviewed)abstract
- The magnetic anisotropy and evolution of striped magnetic domain structures in bcc Fe81Ni19/Co(001) superlattices with the total thickness ranging from 85 to 1370 nm has been studied by magneto-optical Kerr effect and magnetic force microscopy. At a thickness of about 85 nm [25 bilayers (BL)] the domains appear as stripe domains, typical for perpendicular anisotropy films, with the weak cubic anisotropy of the in-plane magnetization component stabilizing the stripe direction. The magnetic domain period strongly depends on the thickness of the superlattice. As the thickness increases, the equilibrium magnetization orients at oblique angles with respect to the film plane and continuously varies with the thickness from in-plane to out-of-plane. We first apply a simple phenomenological model which correctly predicts the transition from in-plane to out-of-plane magnetization as well as increasing domain period and saturation field with increasing BL number. The results indicate the presence of partial flux-closure domains at the film surface with the tilt angle continuously varying with the superlattice thickness. By solving a linearized Landau–Lifshitz equation together with Maxwell’s equations in magnetostatic approximation for samples consisting of up to 1000 individual layers, we calculate the spin-wave dispersion and determine the stability conditions for the saturated ferromagnetic state. From these results the dependence of the saturation field on the number of layers is inferred and agrees well with the experiment. The uniaxial bulk anisotropy is attributed to distortions along the c axis and the results further show evidence for the presence of an easy-plane interface anisotropy in these samples.
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| 17. |
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| 18. |
- Dahlqvist, Martin, et al.
(author)
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Complex magnetism in nanolaminated Mn2GaC
- 2014
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Other publication (other academic/artistic)abstract
- We have used first-principles calculations and Heisenberg Monte Carlo simulations to search for the magnetic ground state of Mn2GaC, a recently synthesized magnetic nanolaminate. We have, independent on method, identified a range of low energy collinear as well as non-collinear magnetic configurations, indicating a highly frustrated magnetic material with several nearly degenerate magnetic states. An experimentally obtained magnetization of only 0.29 per Mn atom in Mn2GaC may be explained by canted spins in an antiferromagnetic configuration of ferromagnetically ordered sub-layers with alternating spin orientation, denoted AFM[0001]. Furthermore, low temperature X-ray diffraction show a new basal plane peak appearing upon a magnetic transition, which is consistent with the here predicted change in inter-layer spacing for the AFM[0001] configuration.
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| 19. |
- Dahlqvist, Martin, et al.
(author)
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Magnetically driven anisotropic structural changes in the atomic laminate Mn2GaC
- 2016
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In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 93:1
-
Journal article (peer-reviewed)abstract
- Inherently layered magnetic materials, such as magnetic M(n+1)AX(n) (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition M(n+1)AX(n) consists of M(n+1)AX(n) blocks separated by atomically thin A-layers where M is a transition metal, A an A-group element, X refers to carbon and/or nitrogen, and n is typically 1, 2, or 3. Here, we show that the recently discovered magnetic Mn2GaC MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of Mn2GaC MAX phases in future magnetoelectric and magnetocaloric applications.
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| 20. |
- Devishvili, A., et al.
(author)
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SuperADAM : Upgraded polarized neutron reflectometer at the Institut Laue-Langevin
- 2013
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 84:2, s. 025112-
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Journal article (peer-reviewed)abstract
- A new neutron reflectometer SuperADAM has recently been built and commissioned at the Institut Laue-Langevin, Grenoble, France. It replaces the previous neutron reflectometer ADAM. The new instrument uses a solid state polarizer/wavelength filter providing a highly polarized (up to 98.6%) monochromatic neutron flux of 8 x 10(4) n cm(-2) s(-1) with monochromatization Delta lambda/lambda = 0.7% and angular divergence Delta alpha = 0.2 mrad. The instrument includes both single and position sensitive detectors. The position sensitive detector allows simultaneous measurement of specular reflection and off-specular scattering. Polarization analysis for both specular reflection and off-specular scattering is achieved using either mirror analyzers or a He-3 spin filter cell. High efficiency detectors, low background, and high flux provides a dynamic range of up to seven decades in reflectivity. Detailed specifications and the instrument capabilities are illustrated with examples of recently collected data in the fields of thin film magnetism and thin polymer films.
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| 21. |
- Eastwood, D. S., et al.
(author)
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X-ray scattering from two-dimensionally patterned magnetic thin film nanoscale arrays
- 2007
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In: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 41:2-3, s. 163-167
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Journal article (peer-reviewed)abstract
- Thin metallic films patterned into nanoscale periodic arrays give rise to coherent satellites on either side of the specular reflection when illuminated at grazing incidence with x-rays. We have used grazing incidence x-ray scattering to probe the crystallography of two-dimensional patterned arrays. Excellent agreement is obtained between experimental scattering profiles and those simulated using a fast Fourier transform method. The technique is appropriate to any shape of patterned element. It is shown that the symmetry of the satellites in an azimuthal rotation map of the scattered intensity provides a sensitive means of measuring symmetry of the two-dimensional order in patterned nanostructures. Furthermore, the in-plane coherence length of the array is found to determine the lineshape of the coherent satellite peaks. We find very good agreement between experimental and simulated rotation maps for the two dimensional array.
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| 22. |
- Fraerman, A. A., et al.
(author)
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Artificial helix nanomagnets
- 2008
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In: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 103, s. 073916-
-
Journal article (peer-reviewed)
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| 23. |
- Fraerman, A. A., et al.
(author)
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Magnetic force microscopy of helical states in multilayer nanomagnets
- 2008
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:7, s. 073916-
-
Journal article (peer-reviewed)abstract
- We have used magnetic force microscopy (MFM) to investigate noncollinear helical states in multilayer nanomagnets, consisting of a stack of single domain ferromagnetic disks separated by insulating nonmagnetic spacers. The nanomagnets were fabricated from a [Co/Si]x3 multilayer thin film structure by electron beam lithography and ion beam etching. The structural parameters (Co layer and spacer thicknesses) were optimized to obtain a clear spiral signature in the MFM contrast, taking into account the magnetostatic interaction between the layers. MFM contrast corresponding to the helical states with different helicities was observed for the optimized structure with Co layer thicknesses of 16, 11, and 8 nm, and with 3 nm Si spacer thickness.
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| 24. |
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| 25. |
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| 26. |
- Haferman, H., et al.
(author)
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Competing anisotropies in bcc Fe81Ni19/Co(001) superlattices
- 2009
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:7, s. 073102-073102-3
-
Journal article (peer-reviewed)abstract
- Amagnetization reorientation transition has been observed in Fe81Ni19/Co(001) superlattices bymeans of magneto-optical Kerr effect and magnetic force microscopy measurements.The transition is driven by the variation of the interfacedensity. First-principles calculations are combined with a linear stability analysisof the Landau–Lifshitz equation to clarify the mechanism that drivesthe transition. We are able to identify it as beingdriven by competing interface in-plane and uniaxial bulk out-of-plane anisotropies.The origin of the bulk anisotropy is attributed to tetragonaldistortions experimentally observed in these superlattices.
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| 27. |
- Hase, Thomas P. A., et al.
(author)
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Proximity effects on dimensionality and magnetic ordering in Pd/Fe/Pd trialyers
- 2014
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:10, s. 104403-
-
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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| 28. |
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| 29. |
- Ingason, Arni Sigurdur, et al.
(author)
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Magnetic Self-Organized Atomic Laminate from First Principles and Thin Film Synthesis
- 2013
-
In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110
-
Journal article (peer-reviewed)abstract
- he first experimental realization of a magnetic Mn+1AXn (MAX) phase, (Cr0.75Mn0.25)2GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent structural quality. This self-organized atomic laminate is based on the well-known Cr2GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.
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| 30. |
- Iwan, Bianca S, et al.
(author)
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TOF-OFF : A method for determining focal positions in tightly focused free-electron laser experiments by measurement of ejected ions
- 2011
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In: High Energy Density Physics. - : Elsevier BV. - 1574-1818. ; 7:4, s. 336-342
-
Journal article (peer-reviewed)abstract
- Pulse intensities greater than 1017 Watt/cm2 were reached at the FLASH soft X-ray laser in Hamburg, Germany, using an off-axis parabolic mirror to focus 15 fs pulses of 5–70 μJ energy at 13.5 nm wavelength to a micron-sized spot. We describe the interaction of such pulses with niobium and vanadium targets and their deuterides. The beam produced craters in the solid targets, and we measured the kinetic energy of ions ejected from these craters. Ions with several keV kinetic energy were observed from craters approaching 5 μm in depth when the sample was at best focus. We also observed the onset of saturation in both ion acceleration and ablation with pulse intensities exceeding 1016 W/cm2, when the highest detected ion energies and the crater depths tend to saturate with increasing intensity. A general difficulty in working with micron and sub-micron focusing optics is finding the exact focus of the beam inside a vacuum chamber. Here we propose a direct method to measure the focal position to a resolution better than the Rayleigh length. The method is based on the correlation between the energies of ejected ions and the physical dimensions of the craters. We find that the focus position can be quickly determined from the ion time-of-flight (TOF) data as the target is scanned through the expected focal region. The method does not require external access to the sample or venting the vacuum chamber. Profile fitting employed to analyze the TOF data can extend resolution beyond the actual scanning step size.
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| 31. |
- Johansson, Å. A., et al.
(author)
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Intrinsic, n- and p-doped a-Si:H thin films grown by DC magnetron sputtering with doped targets
- 1999
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In: Materials Research Society Symposium Proceedings. - 0272-9172 .- 1946-4274. ; 557, s. 31-36
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Journal article (peer-reviewed)abstract
- Intrinsic, n- and p-type a-Si:H films were deposited by dc magnetron sputtering and analyzed with several techniques. The films were synthesized in a reactive Ar-Ha atmosphere giving H contents in the range of 3-20 at %. The films were sputtered from pure silicon targets and doped silicon targets with 1 at % B or P. Doping by co-sputtering from composite Si/B4C targets was also explored. The doping concentrations were 3 × 1020 - 2 × 1021 cm-3 for the p-type films and 2.6-2.9 × 1019cm-3 for the n-type films. The conductivity was in the range lO'MO"4 cm-1 for p-doped films and 10-5 Cl cm-1 for the best n-doped films. Band gap estimations were obtained from dielectric function data and showed an increase with hydrogen content. A comparison to device quality PECVD-samples was also made.
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| 32. |
- Kapaklis, Vassilios, et al.
(author)
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Thermal fluctuations in artificial spin ice
- 2014
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In: Nature Nanotechnology. - 1748-3387 .- 1748-3395. ; 9:7, s. 514-519
-
Journal article (peer-reviewed)abstract
- Artificial spin ice systems have been proposed as a playground for the study of monopole-like magnetic excitations(1,2), similar to those observed in pyrochlore spin ice materials(3). Currents of magnetic monopole excitations have been observed's, demonstrating the possibility for the realization of magnetic-charge-based circuitry. Artificial spin ice systems that support thermal fluctuations can serve as an ideal setting for observing dynamical effects such as monopole propagation and as a potential medium for magnetricity investigations(1,2). Here, we report on the transition from a frozen to a dynamic state in artificial spin ice with a square lattice. Magnetic imaging is used to determine the magnetic state of the islands in thermal equilibrium. The temperature-induced onset of magnetic fluctuations and excitation populations are shown to depend on the lattice spacing and related interaction strength between islands. The excitations are described by Boltzmann distributions with their factors in the frozen state relating to the blocking temperatures of the array. Our results provide insight into the design of thermal artificial spin ice arrays where the magnetic charge density and response to external fields can be studied in thermal equilibrium.
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| 33. |
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| 34. |
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| 35. |
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| 36. |
- Magnus, Fridrik, et al.
(author)
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Giant magnetic domains in amorphous SmCo thin films
- 2014
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:22, s. 224420-1-224420-5
-
Journal article (peer-reviewed)abstract
- The potential for tuning of magnetic properties and the exceptional uniformity are among the features that make amorphous magnetic materials attractive for technology. Here it is shown that the magnetization reversal in amorphous SmCo thin films takes place through the formation of giant magnetic domains, over a centimeter across. The domain structure is found to be dictated by the direction of the imprinted in-plane easy axis and the film boundaries. This is a consequence of the size of the anisotropy and the structural uniformity of the films, which also allows the movement of millimeter-long domain walls over distances of several millimeters. The results demonstrate the possibility of tailoring the magnetic domain structure in amorphous magnets over a wide range of length scales, up to centimeters. Moreover, they highlight an important consequence of the structural perfection of amorphous films.
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| 37. |
- Magnus, Fridrik, et al.
(author)
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Tuneable exchange-spring stiffness in amorphous magnetic trilayer structures
- 2021
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In: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 33:44
-
Journal article (peer-reviewed)abstract
- We investigate the magnetic properties of amorphous Sm10Co90/Co-60(Al70Zr30)(40)/Co-85(Al70Zr30)(15) exchange-spring magnet trilayers. The magnetically soft Co-85(Al70Zr30)(15) layer is coupled to the magnetically hard Sm10Co90 layer through the weakly magnetic low-T (c) Co-60(Al70Zr30)(40) spacer layer. The strength of the coupling can be controlled with temperature and the coupling persists above the intrinsic T (c) of the spacer layer due to a long-range magnetic proximity effect. Polarized neutron reflectivity is used to examine the magnetic profile of the trilayers during magnetization reversal. A two-step switching occurs, with the switching angle of the soft layer strongly dependent on the strength of the coupling. In the strong coupling regime a magnetic state can be achieved where the soft layer magnetization is perpendicular to the hard layer whereas in the weak coupling regime the soft layer reverses fully.
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| 38. |
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| 39. |
- Moubah, Reda, et al.
(author)
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Tailoring magnetism at the nanometer scale in SmCo5 amorphous films
- 2013
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:41, s. 416004-
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Journal article (peer-reviewed)abstract
- The thickness dependence of magnetic properties has been studied in SmCo5 amorphous films with imprinted in-plane anisotropy for thicknesses ranging down to the nanometer scale (2.5-100 nm). The field induced in-plane magnetic anisotropy decreases considerably when the film thickness is below 20 nm. Analysis of the magnetic anisotropy energy shows that the decrease of the induced in-plane anisotropy is accompanied by the development of an out-of-plane interface anisotropy. Two different regimes for the coercivity (H-c) change are found: below 3.75 nm, the H-c decreases continuously with decrease of the film thickness, whereas at above 3.75 nm, the H-c decreases with increase of the film thickness. This change in Hc can be understood by considering the decrease of the short range chemical order for the thinnest films (<3.75 nm) and the relative decrease of the interface contribution with increasing film thickness. The changes in anisotropy have a profound influence on the domain structure, in which the angle of the zigzag domain boundaries decreases with the inverse thickness of the layers.
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| 40. |
- Palonen, Heikki, et al.
(author)
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The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice
- 2019
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In: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 115:1
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Journal article (peer-reviewed)abstract
- The double magnetic proximity effect (MPE) in an Fe/Fe0.30V0.70 superlattice is studied by a direct measurement of the magnetization profile using polarized neutron reflectivity. The experimental magnetization profile is shown to qualitatively agree with a profile calculated using density functional theory. The profile is divided into a short range interfacial part and a long range tail. The interfacial part is explained by charge transfer and induced magnetization, while the tail is attributed to the inhomogeneous nature of the FeV alloy. The long range tail in the magnetization persists up to 170% above the intrinsic ordering temperature of the FeV alloy. The observed effects can be used to design systems with a direct exchange coupling between layers over long distances through a network of connected atoms. When combined with the recent advances in tuning and switching, the MPE with electric fields and currents, the results can be applied in spintronic devices. Published under license by AIP Publishing.
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| 41. |
- Qviller, A. J., et al.
(author)
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Thermal stability of photovoltaic a-Si:H determined by neutron reflectometry
- 2014
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:23, s. 231909-
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Journal article (peer-reviewed)abstract
- Neutron and X-ray reflectometry were used to determine the layer structure and hydrogen content of thin films of amorphous silicon (a-Si:H) deposited onto crystalline silicon (Si) wafers for surface passivation in solar cells. The combination of these two reflectometry techniques is well suited for non-destructive probing of the structure of a-Si:H due to being able to probe buried interfaces and having sub-nanometer resolution. Neutron reflectometry is also unique in its ability to allow determination of density gradients of light elements such as hydrogen (H). The neutron scattering contrast between Si and H is strong, making it possible to determine the H concentration in the deposited a-Si:H. In order to correlate the surface passivation properties supplied by the a-Si:H thin films, as quantified by obtainable effective minority carrier lifetime, photoconductance measurements were also performed. It is shown that the minority carrier lifetime falls sharply when H has been desorbed from a-Si:H by annealing. (C) 2014 AIP Publishing LLC.
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| 42. |
- Rantzer, Annika, 1971-, et al.
(author)
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Optical properties of intrinsic and doped a-Si:H films grown by d.c. magnetron sputter deposition
- 2001
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In: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 394:1-2, s. 255-262
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Journal article (peer-reviewed)abstract
- Thin films of intrinsic, B- and P-doped a-Si:H were grown by d.c. magnetron sputter deposition. The doping was accomplished by doped targets and co-sputtering Si and B4C. Spectroscopic ellipsometry was used for optical characterization and multiple sample analysis was applied to extract the dielectric functions of intrinsic films with 8–10 at.% hydrogen content, boron doped films with 2.2 at.% hydrogen and phosphorous-doped films with hydrogen contents of 10–15 at.%. One of the phosphorous-doped films was micro-crystalline. Hydrogen content was determined by nuclear reaction analysis. From the obtained optical properties the absorption and the optical gap were studied addressing p–i–n diode applications. The optical gaps for intrinsic a-Si:H material were 1.88±0.03 eV as determined by Tauc analysis and 1.45±0.06 eV by applying Cody analysis.
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| 43. |
- Rantzer, Annika, et al.
(author)
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Sputter-deposited a-Si:H for p-i-n photodiodes
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Other publication (other academic/artistic)abstract
- DC magnetron sputter deposition is explored as an alternative for fabricating vertically integrated sensor systems in the form of p-i-n diodes of hydrogenated amorphous silican deposited on CMOS integrated circuit substrates in a post-processing step. We focus here on dopant oncorporation and surface morphological evolution during synthesis of the p-i-n diode sensor structures. The Doping was accomplished using doped targets in a mixed H2/Ar environment. Incorporated P concetrations range from 2.62 to 4.8 x 1019 cm-3 with corresponding conductivities, σ, up to 1.4 x10-5 ohm-1cm-1. B contentrations are between 2.79 and 6.7 X 1020 cm-3 with σ = 4 x 10-5 to 4 x 10-2 ohm-1cm-1. The results of the dopant incorporation are in agreement with reported molecular dynamics simulations. The best intrinsic films have a light to dark conductivity ratio of 102 for white light at an intensity of 10 W/m2. The dark conductivity is a 8 x 10-9 ohm-1cm-1. We conclude that dc magnetron sputter deposition is a good candidate for future device fabrication.
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| 44. |
- Remhof, A., et al.
(author)
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Hydrogen Functionalized Materials
- 2008
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In: Hydrogen as a Future Energy Carrier. - Weinheim : Verlag GmbH & Co. KGaA. - 9783527308170
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Book chapter (other academic/artistic)
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| 45. |
- Rodrigues, Debora C. M., et al.
(author)
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Magnetic anisotropy in permalloy : hidden quantum mechanical features
- 2018
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In: Physical Review B. - 2469-9950 .- 2469-9969. ; 97:22
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Journal article (peer-reviewed)abstract
- By means of relativistic, first principles calculations, we investigate the microscopic origin of the vanishingly low magnetic anisotropy of Permalloy, here proposed to be intrinsically related to the local symmetries of the alloy. It is shown that the local magnetic anisotropy of individual atoms in Permalloy can be several orders of magnitude larger than that of the bulk sample and 5–10 times larger than that of elemental Fe or Ni. We furthermore show that locally there are several easy axis directions that are favored, depending on local composition. The results are discussed in the context of perturbation theory, applying the relation between magnetic anisotropy and orbital moment. Permalloy keeps its pronounced soft ferromagnetic nature due to the exchange energy to be larger than the magnetocrystalline anisotropy. Our results shine light on the magnetic anisotropy of permalloy and of magnetic materials in general, and in addition enhance the understanding of pump-probe measurements and ultrafast magnetization dynamics.
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| 46. |
- Stopfel, Henry, et al.
(author)
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Multiple energy scales in mesospin systems : The vertex-frustrated Saint George lattice
- 2021
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In: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 5:11
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Journal article (peer-reviewed)abstract
- The interplay between topology and energy hierarchy plays a vital role in the collective magnetic order in artificial ferroic systems. Here we investigate, experimentally, the effect of having one or two activation energies of interacting Ising-like magnetic islands—mesospins—in thermalized, vertex-frustrated lattices. The thermally arrested magnetic states of the elements were determined using synchrotron-based magnetic microscopy after cooling the samples from temperatures above the Curie temperature of the material. Statistical analysis of the correlations between mesospins across several length scales reveals changes in the magnetic order, reflecting the amount of ground state plaquettes realized for a vertex-frustrated lattice. We show that the latter depends on the presence, or not, of different activation energies.
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| 47. |
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| 48. |
- Thorarinsdottir, K. A., et al.
(author)
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Finding order in disorder : Magnetic coupling distributions and competing anisotropies in an amorphous metal alloy
- 2022
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In: APL Materials. - : American Institute of Physics (AIP). - 2166-532X. ; 10:4
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Journal article (peer-reviewed)abstract
- Amorphous metals have unusual magnetic properties that arise due to the disordered atomic arrangement. We show that Co-x(Al70Zr30)(100-x) (65 < x < 92 at.%) amorphous alloys have a distribution in the local magnetic coupling and ordering temperature, which can be explained by nanoscale composition variations. We use competing anisotropies induced by the substrate and an applied field during growth to probe the Co concentration distribution. Only regions with high enough Co concentration develop a magnetic anisotropy along the magnetic field during growth, whereas regions of low Co concentration have an anisotropy dictated by the substrate. A Gaussian distribution in the Co concentration of width 5.1 at.% is obtained from the variation in anisotropy. The results demonstrate the importance of composition variations for emergent magnetic properties and have far reaching implications for the properties of disordered materials in general.
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| 49. |
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| 50. |
- Van Kampen, M., et al.
(author)
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On the realization of artificial XY spin chains
- 2005
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In: Journal of Physics. - 0953-8984 .- 1361-648X. ; 17:2, s. L27-L33
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Journal article (peer-reviewed)abstract
- Spin chains are the most elementary entities in the study of magnetic ordering behavior. The authors describe a route toward the realization of artificial XY spin chains. Using thin-film deposition and e-beam lithog., 300 and 550 nm diam. pillars consisting of alternating disks of permalloy and Al2O3 were made. Shape anisotropy forces the magnetization in plane, creating a chain of two-dimensional magnetic moments →i. The disks couple to each other by their dipolar stray fields, resulting in an interaction Jij→i·→j, with Jij the coupling between disks i and j. This form closely resembles a chain of xy spins, coupled by effective interactions Jij. The authors present a magnetic characterization of the pillars, and compare the results with model calcns. Also, spin dynamics and ordering phenomena are addressed.
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