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BETA
Hjörvarsson, BjörgvinORCID iD iconorcid.org/0000-0003-1803-9467
Alternative names
Publications (10 of 257) Show all publications
Qviller, A. J., Marstein, E. S., You, C. C., Haug, H., Webster, J. R. P., Hjörvarsson, B., . . . Hauback, B. C. (2018). Hydrogen Concentration in Photovoltaic a-Si:H Annealed at Different Temperatures Measured by Neutron Reflectometry. IEEE Journal of Photovoltaics, 8(4), 1098-1101
Open this publication in new window or tab >>Hydrogen Concentration in Photovoltaic a-Si:H Annealed at Different Temperatures Measured by Neutron Reflectometry
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2018 (English)In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 8, no 4, p. 1098-1101Article in journal (Refereed) Published
Abstract [en]

Amorphous hydrogenated silicon (a-Si:H) is an important material for surface defect passivation of photovoltaic silicon (Si) wafers in order to reduce their recombination losses. The material is, however, unstable with regard to hydrogen (H) desorption at elevated temperatures, which can be an issue during processing and device manufacturing. In this work, we determine the temperature stability of a-Si:H by structural characterization of a-Si:H/Si bilayers with neutron reflectometry and X-ray reflectometry combined with photoconductance measurements, yielding the minority carrier lifetime. The neutrons are sensitive to light elements such as H, while the X-rays, which are insensitive to the H concentration, provide an independent constraint on the layer structure. It is shown that H desorption takes place at a temperature of approximately T = 425 degrees C, and that the H content and minority carrier lifetimes have a strongly correlated linear relationship, which can be interpreted as one H atom passivating one defect.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
Keywords
Amorphous materials, silicon, solar energy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-359995 (URN)10.1109/JPHOTOV.2018.2838447 (DOI)000436007400027 ()
Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2018-09-14Bibliographically approved
Östman, E., Stopfel, H., Chioar, I.-A., Arnalds, U. B., Stein, A., Kapaklis, V. & Hjörvarsson, B. (2018). Interaction modifiers in artificial spin ices. Nature Physics, 14(4), 375-379
Open this publication in new window or tab >>Interaction modifiers in artificial spin ices
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2018 (English)In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 14, no 4, p. 375-379Article in journal (Refereed) Published
Abstract [en]

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order(1-6), collective low-energy dynamics(7,8) and emergent magnetic properties(5,9,10) in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane(11). We show that by placing these on the vertices of square artificial spin-ice arrays and varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. The work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-352710 (URN)10.1038/s41567-017-0027-2 (DOI)000429434100018 ()
Funder
Knut and Alice Wallenberg Foundation, 2015.0060Swedish Research CouncilEU, Horizon 2020, 737093
Available from: 2018-06-07 Created: 2018-06-07 Last updated: 2018-09-14Bibliographically approved
Rodrigues, D. C. M., B Klautau, A., Edström, A., Rusz, J., Nordström, L., Pereiro, M., . . . Eriksson, O. (2018). Magnetic anisotropy in permalloy: hidden quantum mechanical features. Physical Review B, 97(22), Article ID 224402.
Open this publication in new window or tab >>Magnetic anisotropy in permalloy: hidden quantum mechanical features
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 22, article id 224402Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
Permalloy, Orbital Anisotropy, Anisotropy Energy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-319925 (URN)10.1103/PhysRevB.97.224402 (DOI)000434015300004 ()
Funder
Knut and Alice Wallenberg Foundation, 2012.0031Knut and Alice Wallenberg Foundation, 2013.0020Swedish Research CouncileSSENCE - An eScience CollaborationStandUp
Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2018-09-14Bibliographically approved
Stopfel, H., Östman, E., Chioar, I.-A., Greving, D., Arnalds, U., Hase, T. P. A., . . . Kapaklis, V. (2018). Magnetic order and energy-scale hierarchy in articial spin ice structures. Physical Review B, 98, Article ID 014435.
Open this publication in new window or tab >>Magnetic order and energy-scale hierarchy in articial spin ice structures
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, article id 014435Article in journal (Refereed) Published
Abstract [en]

In order to explain and predict the properties of many physical systems, it is essential to understand the interplay of different energy scales. Here we present investigations of the magnetic order in thermalized artificial spin-ice structures, with different activation energies of the interacting Ising-like elements. We image the thermally equilibrated magnetic states of the nanostructures using synchrotron-based magnetic microscopy. By comparing results obtained from structures with one or two different activation energies, we demonstrate a clear impact on the resulting magnetic order. The differences are obtained by the analysis of the magnetic spin structure factors, in which the role of the activation energies is manifested by distinct short-range order. These results highlight the potential of artificial spin-ice structures to serve as model systems for designing various energy-scale hierarchies and investigating their impact on the collective dynamics and magnetic order.

Keywords
artificial spin ice, magnetic nano-structures, mesoscopic spin systems, mesospins, model systems, Shakti, engineering of energy-landscape, multiple energy-scales
National Category
Condensed Matter Physics Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-329016 (URN)10.1103/PhysRevB.98.014435 (DOI)000440137800003 ()
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Knut and Alice Wallenberg FoundationSwedish Research Council
Note

Title in thesis list of papers: Magnetic order and energy-scale hierarchy in articial spin ice

Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2018-10-08Bibliographically approved
Holmberg, M., Dancila, D., Rydberg, A., Hjörvarsson, B., Jansson, U., Marattukalam, J. J., . . . Andersson, J. (2018). On Surface Losses in Direct Metal Laser Sintering Printed Millimeter and Submillimeter Waveguides. Journal of Infrared, Millimeter and Terahertz Waves, 39(6), 535-545
Open this publication in new window or tab >>On Surface Losses in Direct Metal Laser Sintering Printed Millimeter and Submillimeter Waveguides
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2018 (English)In: Journal of Infrared, Millimeter and Terahertz Waves, ISSN 1866-6892, E-ISSN 1866-6906, Vol. 39, no 6, p. 535-545Article in journal (Refereed) Published
Abstract [en]

Different lengths of WR3 (220-330 GHz) and WR10 (75-110 GHz) waveguides are fabricated through direct metal laser sintering (DMLS). The losses in these waveguides are measured and modelled using the Huray surface roughness model. The losses in WR3 are around 0.3 dB/mm and in WR10 0.05 dB/mm. The Huray equation model is accounting relatively good for the attenuation in the WR10 waveguide but deviates more in the WR3 waveguide. The model is compared to finite element simulations of the losses assuming an approximate surface structure similar to the resulting one from the DMLS process.

Place, publisher, year, edition, pages
SPRINGER, 2018
Keywords
Millimeterwave, 3D-metal-printed, Waveguide loss
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-356385 (URN)10.1007/s10762-018-0470-x (DOI)000431255500005 ()
Funder
Swedish Foundation for Strategic Research
Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2018-07-25Bibliographically approved
Magnus, F., Warnatz, T., Pálsson, G. K., Devishvili, A., Ukleev, V., Palisaitis, J., . . . Hjörvarsson, B. (2018). Sequential magnetic switching in Fe/MgO(001) superlattices. Physical Review B. Condensed Matter and Materials Physics, 97, Article ID 174424.
Open this publication in new window or tab >>Sequential magnetic switching in Fe/MgO(001) superlattices
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2018 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 97, article id 174424Article in journal (Refereed) Published
Abstract [en]

Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchangecoupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90◦periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the toplayer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180◦periodic alignment isobtained at remanence and with increasing applied field the layer switching starts from the two outermost layersand proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensionalmagnetic structures with a predefined discrete switching sequence

Place, publisher, year, edition, pages
American Physical Society, 2018
Keywords
Magnetization Switching, Neutron Reflectometry, Superlattice, Magnetic Multilayer, Exchange Interaction, Coupling
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-352463 (URN)10.1103/PhysRevB.97.174424 (DOI)000433028500004 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research , RIF-0074
Available from: 2018-06-05 Created: 2018-06-05 Last updated: 2018-09-14Bibliographically approved
Huang, W., Mooij, L. P. A., Droulias, S. A., Palonen, H., Hartmann, O., Pálsson, G. K., . . . Hjörvarsson, B. (2017). Concentration dependence of hydrogen diffusion in clamped vanadium (001) films. Journal of Physics: Condensed Matter, 29(4), Article ID 045402.
Open this publication in new window or tab >>Concentration dependence of hydrogen diffusion in clamped vanadium (001) films
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2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 4, article id 045402Article in journal (Refereed) Published
Abstract [en]

The chemical diffusion coefficient of hydrogen in a 50 nm thin film of vanadium (0 0 1) is measured as a function of concentration and temperature, well above the known phase boundaries. Arrhenius analysis of the tracer diffusion constants reveal large changes in the activation energy with concentration: from 0.10 at 0.05 in II V-1 to 0.5 eV at 0.2 in II V-1. The results are consistent with a change from tetrahedral to octahedral site occupancy, in that concentration range. The change in site occupancy is argued to be caused by the uniaxial expansion of the film originating from the combined hydrogen induced expansion and the clamping of the film to the substrate.

Keywords
diffusion, hydrogen, single crystal
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-312024 (URN)10.1088/1361-648X/29/4/045402 (DOI)000389233200001 ()
Funder
Swedish Energy AgencySwedish Research Council
Available from: 2017-01-05 Created: 2017-01-04 Last updated: 2018-09-14Bibliographically approved
Droulias, S. A., Pálsson, G. K., Palonen, H., Ali, H., Leifer, K., Kapaklis, V., . . . Wolff, M. (2017). Crystal perfection by strain engineering: The case of Fe/V (001). Thin Solid Films, 636, 608-614
Open this publication in new window or tab >>Crystal perfection by strain engineering: The case of Fe/V (001)
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2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 636, p. 608-614Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
Superlattice; Iron/Vanadium; Sputtering; Epitaxy; Reciprocal space mapping; X-ray diffraction; X-ray reflectivity; Linear elasticity
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-332050 (URN)10.1016/j.tsf.2017.07.005 (DOI)000408037800086 ()
Available from: 2017-10-23 Created: 2017-10-23 Last updated: 2018-05-14Bibliographically approved
Huang, W., Palonen, H., Droulias, S. A., Hartmann, O., Wolff, M. & Hjörvarsson, B. (2017). Diffusion of hydrogen in ultra-thin V(001) layers. Journal of Alloys and Compounds, 723, 484-487
Open this publication in new window or tab >>Diffusion of hydrogen in ultra-thin V(001) layers
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2017 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 723, p. 484-487Article in journal (Refereed) Published
Abstract [en]

We report on investigations of the influence of one dimensional confinement on the diffusion of hydrogen, in the low concentration limit (alpha-phase). The confinement is obtained by utilising single crystal Fe/V(001) superlattices, in which hydrogen preferably resides in the V layers. The diffusion along the [110] direction in the V(001) layers can thereby be determined. Activation energy and attempt jump rates are extracted from an Arrhenius analysis. No effects are observed from the confinement on the hydrogen diffusion in the thickness range 7-28 monolayers (approximate to 1.1-4.2 nm) of V(001).

Keywords
Confinement, Optical transmission, Diffusion, Interstitials
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-333734 (URN)10.1016/j.jallcom.2017.06.194 (DOI)000407009400062 ()
Available from: 2017-11-20 Created: 2017-11-20 Last updated: 2018-09-14Bibliographically approved
Huang, W., Pálsson, G. K., Brischetto, M., Droulias, S. A., Hartmann, O., Wolff, M. & Hjörvarsson, B. (2017). Experimental observation of hysteresis in a coherent metal-hydride phase transition. Journal of Physics: Condensed Matter, 29(49), Article ID 495701.
Open this publication in new window or tab >>Experimental observation of hysteresis in a coherent metal-hydride phase transition
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2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 49, article id 495701Article in journal (Refereed) Published
Abstract [en]

We investigate the hysteresis obtained in the hydrogen absorption and desorption cycle for a single crystal Pd/V-28 [Fe-4/V-28](11) superlattice. Below the critical temperature, a small but clear hysteresis is observed in the pressure-composition isotherms, while it is absent above. The experimental results thereby prove the relevance of macroscopic energy barriers for obtaining hysteresis in coherent structural transformations. The textured Pd layer exhibits substantially larger hysteresis effects, which can be related to an irreversible energy loss caused by defect generation in Pd.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keywords
hysteresis, coherent, incoherent, phase transition
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-342651 (URN)10.1088/1361-648X/aa9696 (DOI)000415854900001 ()
Funder
Swedish Energy AgencySwedish Research Council
Available from: 2018-02-28 Created: 2018-02-28 Last updated: 2018-05-14Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1803-9467

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