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Hjörvarsson, BjörgvinORCID iD iconorcid.org/0000-0003-1803-9467
Alternative names
Publications (10 of 269) Show all publications
Warnatz, T., Skovdal, B. E., Magnus, F., Stopfel, H., Primetzhofer, D., Stein, A., . . . Hjörvarsson, B. (2020). The influence of diameter on the magnetic saturation in Fe 84 Cu 16 /MgO [001] multilayered islands. Journal of Magnetism and Magnetic Materials, 496, Article ID 165864.
Open this publication in new window or tab >>The influence of diameter on the magnetic saturation in Fe 84 Cu 16 /MgO [001] multilayered islands
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2020 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 496, article id 165864Article in journal (Refereed) Published
Abstract [en]

The saturation field of circular islands, consisting of [Fe84Cu16/MgO]9Fe84Cu16 multilayers, increases with decreasing diameter of the islands. When the diameter of the islands is below 450 nm the field induced changes are dominated by a coherent rotation of the moment of the Fe84Cu16 layers. For diameters of 2 μm and larger, a signature of domain nucleation and evolution is observed. The changes in the saturation field with diameter of the islands are ascribed to the interplay between interlayer exchange coupling, stray field coupling at the edges and the crystalline anisotropy of the Fe84Cu16 layers.

Keywords
finite size, patterning, interlayer exchange, coupling, magnetic multilayer
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-394276 (URN)10.1016/j.jmmm.2019.165864 (DOI)000491941800003 ()
Funder
Swedish Research Council, 821-2012-5144Swedish Foundation for Strategic Research , RIF14-0053Knut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2019-10-07 Created: 2019-10-07 Last updated: 2019-11-15Bibliographically approved
Pacheco, V., Karlsson, D., Marattukalam, J. J., Stolpe, M., Hjörvarsson, B., Jansson, U. & Sahlberg, M. (2020). Thermal stability and crystallization of a Zr-based metallic glass produced by suction casting and selective laser melting. Journal of Alloys and Compounds, 825, Article ID 153995.
Open this publication in new window or tab >>Thermal stability and crystallization of a Zr-based metallic glass produced by suction casting and selective laser melting
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2020 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 825, article id 153995Article in journal (Refereed) Published
Abstract [en]

The thermal stability and crystallization mechanism of the Zr59.3Cu28.8Al10.4Nb1.5 (at%) metallic glass produced through selective laser melting SLM (from industrial grade material) was studied and compared with the same alloy produced by suction casting (from laboratory grade material of high purity). Oxygen- and Al-rich particles of a cubic phase (Fd (3) over barm) with a size of up to 200 nm are detected in the as-built selective laser melted samples by transmission electron microscopy. The crystallization process of the cast and SLM samples is investigated by in-situ X-ray diffraction experiments. In the cast samples, the initial crystallization occurs via the formation of a metastable tetragonal phase (Al2Zr3), together with tetragonal CuZr2 and hexagonal Al3Zr4 type structures, while the SLM samples initially crystallize through the formation of the metastable, oxygen- and Al-rich, cubic phase already present before annealing. The main phases present at the end of the crystallization for both type of samples are the same, mainly CuZr2 and Al3Zr4. The differences in the crystallization paths are attributed to differences in the oxygen levels. In general, the higher oxygen content (similar to 1 at%) of the SLM samples results in a decrease of the thermal stability of the alloy and promotes the formation of an oxygen-rich, metastable cubic phase. 

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2020
Keywords
Metallic glass, Additive manufacturing, Selective laser melting, Laser beam powder bed fusion, Crystallization, Thermal stability
National Category
Metallurgy and Metallic Materials Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-407503 (URN)10.1016/j.jallcom.2020.153995 (DOI)000514848600109 ()
Funder
Swedish Foundation for Strategic Research , GSn15-0008Swedish Foundation for Strategic Research , GMT14-0048
Available from: 2020-03-26 Created: 2020-03-26 Last updated: 2020-03-26Bibliographically approved
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
Conlon, C. S., Conti, G., Nemsak, S., Pálsson, G. K., Moubah, R., Kuo, C.-T. -., . . . Fadley, C. S. (2019). Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction. Journal of Applied Physics, 126(7), Article ID 075305.
Open this publication in new window or tab >>Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction
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2019 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 126, no 7, article id 075305Article in journal (Refereed) Published
Abstract [en]

The Fe/MgO magnetic tunnel junction is a classic spintronic system, with current importance technologically and interest for future innovation. The key magnetic properties are linked directly to the structure of hard-to-access buried interfaces, and the Fe and MgO components near the surface are unstable when exposed to air, making a deeper probing, nondestructive, in-situ measurement ideal for this system. We have thus applied hard x-ray photoemission spectroscopy (HXPS) and standing-wave (SW) HXPS in the few kilo-electron-volt energy range to probe the structure of an epitaxially grown MgO/Fe superlattice. The superlattice consists of 9 repeats of MgO grown on Fe by magnetron sputtering on an MgO(001) substrate, with a protective Al2O3 capping layer. We determine through SW-HXPS that 8 of the 9 repeats are similar and ordered, with a period of 33 +/- 4 angstrom, with the minor presence of FeO at the interfaces and a significantly distorted top bilayer with ca. 3 times the oxidation of the lower layers at the top MgO/Fe interface. There is evidence of asymmetrical oxidation on the top and bottom of the Fe layers. We find agreement with dark-field scanning transmission electron microscope (STEM) and x-ray reflectivity measurements. Through the STEM measurements, we confirm an overall epitaxial stack with dislocations and warping at the interfaces of ca. 5 angstrom. We also note a distinct difference in the top bilayer, especially MgO, with possible Fe inclusions. We thus demonstrate that SW-HXPS can be used to probe deep buried interfaces of novel magnetic devices with few-angstrom precision.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-394269 (URN)10.1063/1.5089556 (DOI)000483849000004 ()
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-10-09Bibliographically 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: 2019-12-06Bibliographically 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
Ali, H., Warnatz, T., Xie, L., Hjörvarsson, B. & Leifer, K. (2019). Towards Quantitative Nanomagnetism in Transmission Electron Microscope by the Use of Patterned Apertures. Paper presented at Microscopy and Microanalysis, Portland, August 4-8, 2019.. Microscopy and Microanalysis, 25(S2), 654-655
Open this publication in new window or tab >>Towards Quantitative Nanomagnetism in Transmission Electron Microscope by the Use of Patterned Apertures
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2019 (English)In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 25, no S2, p. 654-655Article in journal, Meeting abstract (Other academic) Published
National Category
Nano Technology
Identifiers
urn:nbn:se:uu:diva-395344 (URN)10.1017/S1431927619004008 (DOI)
Conference
Microscopy and Microanalysis, Portland, August 4-8, 2019.
Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-10-25Bibliographically 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
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1803-9467

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