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BETA
Hjörvarsson, BjörgvinORCID iD iconorcid.org/0000-0003-1803-9467
Alternative names
Publications (10 of 265) Show all publications
Ciuciulkaite, A., Östman, E., Brucas, R., Kumar, A., Verschuuren, M. A., Svedlindh, P., . . . Kapaklis, V. (2019). Collective magnetization dynamics in nanoarrays of thin FePd disks. Physical Review B, 99(18), Article ID 184415.
Open this publication in new window or tab >>Collective magnetization dynamics in nanoarrays of thin FePd disks
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 18, article id 184415Article in journal (Refereed) Published
Abstract [en]

We report on the magnetization dynamics of a square array of mesoscopic disks, fabricated from an iron palladium alloy film. The dynamics properties were explored using ferromagnetic resonance measurements and micromagnetic simulations. The obtained spectra exhibit features resulting from the interactions between the disks, with a clear dependence on both temperature and the direction of the externally applied field. We demonstrate a qualitative agreement between the measured and calculated spectra. Furthermore, we calculated the mode profiles of the standing spin waves excited during time-dependent magnetic field excitations. The resulting maps confirm that the features appearing in the ferromagnetic resonance absorption spectra originate from the temperature- and directional-dependent interdisk interactions.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-386163 (URN)10.1103/PhysRevB.99.184415 (DOI)000468206200003 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)EU, Horizon 2020, 737093
Available from: 2019-06-20 Created: 2019-06-20 Last updated: 2019-06-20Bibliographically approved
Thorarinsdottir, K. A., Palonen, H., Pálsson, G. K., Hjörvarsson, B. & Magnus, F. (2019). Giant magnetic proximity effect in amorphous layered magnets. PHYSICAL REVIEW MATERIALS, 3(5), Article ID 054409.
Open this publication in new window or tab >>Giant magnetic proximity effect in amorphous layered magnets
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2019 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, no 5, article id 054409Article in journal (Refereed) Published
Abstract [en]

Here we study the magnetic proximity effect in amorphous layered magnets of alternating high- and low-T-c materials using magnetometry and polarized neutron reflectivity. By altering the thickness of either the high-or low-T-c layer we are able to extract the induced magnetic moment in the low-T-c layer directly and study how it scales with thickness. We observe that the ordering temperature of the low-T-c layer is enhanced and above which a second magnetically ordered state with a very large extension is observed. This induced magnetic state survives to a temperature at least three times that of the ordering temperature of the low-T-c layer and the induced magnetization is approximately constant throughout at least a 10-nm-thick layer. The induced magnetic region within the low-T-c layer does not depend on the thickness of the adjacent high-T-c layer.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-387591 (URN)10.1103/PhysRevMaterials.3.054409 (DOI)000469048500002 ()
Funder
Swedish Research Council
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-06-26Bibliographically approved
Ali, H., Warnatz, T., Xie, L., Hjörvarsson, B. & Leifer, K. (2019). Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS. Ultramicroscopy, 196, 192-196
Open this publication in new window or tab >>Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS
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2019 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 196, p. 192-196Article in journal (Refereed) Published
Abstract [en]

The weak signal strength in electron magnetic circular dichroism (EMCD) measurements remains one of the main challenges in the quantification of EMCD related EELS spectra. As a consequence, small variations in peak intensity caused by changes of background intervals, choice of method for extraction of signal intensity and equally differences in sample quality can cause strong changes in the EMCD signal. When aiming for high resolution quantitative EMCD, an additional difficulty consists in the fact that the two angular resolved EELS spectra needed to obtain the EMCD signal are taken at two different instances and it cannot be guaranteed that the acquisition conditions for these two spectra are identical.  Here, we present an experimental setup where we use a double hole aperture in the transmission electron microscope to obtain the EMCD signal in a single acquisition. This geometry allows for the parallel acquisition of the two electron energy loss spectra (EELS) under exactly the same conditions. We also compare the double aperture acquisition mode with the qE acquisition mode which has been previously used for parallel acquisition of EMCD. We show that the double aperture mode not only offers better signal to noise ratio as compared to qE mode but also allows for much higher acquisition times to significantly improve the signal quality which is crucial for quantitative analysis of the magnetic moments.

National Category
Other Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-364715 (URN)10.1016/j.ultramic.2018.10.012 (DOI)000451180800026 ()30439606 (PubMedID)
Funder
Swedish Research Council, C0367901Swedish Research Council, 2016-05259Knut and Alice Wallenberg Foundation
Available from: 2018-10-31 Created: 2018-10-31 Last updated: 2019-01-28Bibliographically approved
Huang, W., Brischetto, M. & Hjörvarsson, B. (2019). Size effect on deuterium behavior in nano-sized vanadium layers. SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY, 62(11), Article ID 117011.
Open this publication in new window or tab >>Size effect on deuterium behavior in nano-sized vanadium layers
2019 (English)In: SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY, ISSN 1674-7348, Vol. 62, no 11, article id 117011Article in journal (Refereed) Published
Abstract [en]

Size effect on thermodynamics and diffusion of deuterium in nano-sized vanadium (V) layers is studied. Critical temperature (T-c) for deuterium phase transition is found to decrease with the inverse thickness of V layers and the thermodynamic factor increases as V thickness decreases. These effects are related to the deuterium-deuterium (D-D) interaction change versus V thickness, which experimentally proves that the D-D interaction plays the main contribution to the previously observed V size effect on deuterium chemical diffusion coefficients (D-c). The self-diffusion coefficients (D-s) are obtained through correcting D-c with the thermodynamic factors. It is found that the D-s are similar in 14 and 28 monolayers of V while slightly larger D-s are observed at high concentrations in 14 atomic layers. The weak site blocking effect in the interface is argued to be the main contribution to the observed size effect on D-s.

Keywords
size effect, D-D interaction, deuterium diffusion, Fe/V superlattice, optical transmission
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-383494 (URN)10.1007/s11433-018-9381-8 (DOI)000466398100001 ()
Funder
Swedish Energy AgencySwedish Research Council
Available from: 2019-05-17 Created: 2019-05-17 Last updated: 2019-05-17Bibliographically approved
Palonen, H., Mukhamedov, B. O., Ponomareva, A. V., Pálsson, G. K., Abrikosov, I. A. & Hjörvarsson, B. (2019). The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice. Applied Physics Letters, 115(1), Article ID 012406.
Open this publication in new window or tab >>The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice
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2019 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 115, no 1, article id 012406Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-390904 (URN)10.1063/1.5102121 (DOI)000474211400020 ()
Funder
Swedish Research Council
Available from: 2019-08-19 Created: 2019-08-19 Last updated: 2019-08-19Bibliographically approved
Holmberg, M., Dancila, D., Rydberg, A., Hjörvarsson, B., Jansson, U., Marattukalam, J. J., . . . Andersson, J. (2018). Direct metal laser sintering printed millimeter and submillimeter waveguides. In: : . Paper presented at GigaHertz Symposium, Lund, May 24-25 2018.
Open this publication in new window or tab >>Direct metal laser sintering printed millimeter and submillimeter waveguides
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2018 (English)Conference paper, Poster (with or without abstract) (Other academic)
National Category
Telecommunications
Identifiers
urn:nbn:se:uu:diva-369172 (URN)
Conference
GigaHertz Symposium, Lund, May 24-25 2018
Funder
Swedish Foundation for Strategic Research , GMT14-0048
Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-11Bibliographically approved
Palonen, H., Magnus, F. & Hjörvarsson, B. (2018). Double magnetic proximity in Fe/Fe0.32V0.68 superlattices. Physical Review B, 98(14), Article ID 144419.
Open this publication in new window or tab >>Double magnetic proximity in Fe/Fe0.32V0.68 superlattices
2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 14, article id 144419Article in journal (Refereed) Published
Abstract [en]

The conventional magnetic proximity effect and double-proximity effects were studied in a set of fully coherent high-quality Fe/Fe0.32V0.68 superlattices. Applying a simple model to the saturation magnetization, it is seen that the magnetic proximity effect is gigantic in magnitude in the alloy-the magnetization is enhanced by 20-450 % and the ordering temperature is enhanced by a factor of 2. The magnitude of the effect can be explained by the large susceptibility of the alloy above its intrinsic ordering temperature. Additionally, a strong dependence of the ordering temperature of single monolayers of Fe on the interlayer distance is observed. The results give insight into new ways of using alloying and large magnetic susceptibility combined with magnetic proximity effects to enhance the functionality of materials that are of interest for spintronic devices.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-368444 (URN)10.1103/PhysRevB.98.144419 (DOI)000447183100005 ()
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2018-12-07Bibliographically approved
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
Droulias, S. A., Pálsson, G. K., Hjörvarsson, B. & Wolff, M. (2018). Limitations of the kinematic approximation in neutron reflectivity measurements for the analysis of bilayers. Journal of applied crystallography, 51, 1556-1563
Open this publication in new window or tab >>Limitations of the kinematic approximation in neutron reflectivity measurements for the analysis of bilayers
2018 (English)In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 51, p. 1556-1563Article in journal (Refereed) Published
Abstract [en]

The limitations of a phenomenological fitting approach compared to simulations of the optical model including reflection and refraction at all interfaces are demonstrated using the example of hydrogen loading in ultra-thin vanadium layers. Fe/V superlattices are loaded with deuterium and the lattice expansion and deuterium concentration are extracted from neutron reflectivity data. A noticeable difference is found between the extraction of concentrations and bilayer thicknesses directly from the superlattice peaks and fits of the density profile using the Parratt formalism. The results underline the importance of carefully considering the limitations of phenomenological approaches, in order to obtain robust results. The limitations of the kinematic approximation for the analysis are discussed in detail.

Place, publisher, year, edition, pages
INT UNION CRYSTALLOGRAPHY, 2018
Keywords
neutron reflectivity, superlattices, deuterium, volume expansion, Parratt's algorithm
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-372377 (URN)10.1107/S1600576718013092 (DOI)000451833600006 ()
Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-01-08Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1803-9467

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