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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., 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
Huang, W., Pálsson, G. K., Brischetto, M., Palonen, H., Droulias, S. A., Hartmann, O., . . . Hjörvarsson, B. (2017). Finite size effects: deuterium diffusion in nm thick vanadium layers. New Journal of Physics, 19, Article ID 123004.
Open this publication in new window or tab >>Finite size effects: deuterium diffusion in nm thick vanadium layers
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2017 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 19, article id 123004Article in journal (Refereed) Published
Abstract [en]

We investigate the effect of finite size on the chemical diffusion of deuterium in extremely thin V(001) layers. A five fold increase in the diffusion coefficient is observed at concentrations around 0.2 [D/V], when the thickness of the V is decreased from 28 to 14 atomic layers (approximate to 2.1-4.2 nm). The size dependent deuterium-deuterium interaction energy is argued to be the root of the observed changes as the diffusion rates are similar at low concentrations. The results demonstrate the feasibility of using finite-size effects to enhance the chemical diffusion of light interstitials in solids. We discuss the general applicability of these effects to other systems.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017
Keywords
superlattices, optical transmission, deuterium diffusion, octahedral sites
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-347665 (URN)10.1088/1367-2630/aa94df (DOI)000424885300004 ()
Funder
Swedish Energy AgencySwedish Research Council
Available from: 2018-04-05 Created: 2018-04-05 Last updated: 2018-05-14Bibliographically approved
Mooij, L., Huang, W., Droulias, S. A., Johansson, R., Hartmann, O., Xin, X., . . . Hjörvarsson, B. (2017). The influence of site occupancy on diffusion of hydrogen in vanadium. Physical Review B, 95(6), Article ID 064310.
Open this publication in new window or tab >>The influence of site occupancy on diffusion of hydrogen in vanadium
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 6, article id 064310Article, review/survey (Refereed) Published
Abstract [en]

We investigate the effect of site occupancy on the chemical diffusion of hydrogen in strained vanadium. The diffusion rate is found to decrease substantially, when hydrogen is occupying octahedral sites as compared to tetrahedral sites. Profound isotope effects are observed when comparing the diffusion rate of H and D. The changes in the diffusion rate are found to be strongly influenced by the changes in the potential energy landscape, as deduced from first-principles molecular dynamics calculations.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-275058 (URN)10.1103/PhysRevB.95.064310 (DOI)000395988800002 ()
Note

The manuscript version of this article is part of two PhD theses: http://uu.diva-portal.org/smash/record.jsf?pid=diva2:900624

http://uu.diva-portal.org/smash/record.jsf?pid=diva2:950756

Available from: 2016-01-28 Created: 2016-01-28 Last updated: 2018-05-14Bibliographically approved
Thersleff, T., Muto, S., Werwinski, M., Spiegelberg, J., Kvashnin, Y., Hjörvarsson, B., . . . Leifer, K. (2017). Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface. Scientific Reports, 7, Article ID 44802.
Open this publication in new window or tab >>Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 44802Article in journal (Refereed) Published
Abstract [en]

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2017
National Category
Atom and Molecular Physics and Optics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-320197 (URN)10.1038/srep44802 (DOI)000397288700001 ()28338011 (PubMedID)
Funder
Swedish Research Council, C0367901The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2009-2017Knut and Alice Wallenberg Foundation, 2013.0020 2012.0031eSSENCE - An eScience Collaboration
Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2018-04-11Bibliographically approved
Arnalds, U. B., Chico, J., Stopfel, H., Kapaklis, V., Bärenbold, O., Verschuuren, M. A., . . . Hjörvarsson, B. (2016). A new look on the two-dimensional Ising model: thermal artificial spins. New Journal of Physics, 18, Article ID 023008.
Open this publication in new window or tab >>A new look on the two-dimensional Ising model: thermal artificial spins
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2016 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 18, article id 023008Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
magnetic ordering, artificial spins, Ising model
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-288634 (URN)10.1088/1367-2630/18/2/023008 (DOI)000372453700002 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2016-05-04 Created: 2016-04-28 Last updated: 2017-11-30Bibliographically approved
Callini, E., Atakli, Z. O., Hauback, B. C., Orimo, S.-i., Jensen, C., Dornheim, M., . . . Zuettel, A. (2016). Complex and liquid hydrides for energy storage. Applied Physics A: Materials Science & Processing, 122(4), Article ID 353.
Open this publication in new window or tab >>Complex and liquid hydrides for energy storage
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2016 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 122, no 4, article id 353Article in journal (Refereed) Published
Abstract [en]

The research on complex hydrides for hydrogen storage was initiated by the discovery of Ti as a hydrogen sorption catalyst in NaAlH4 by Boris Bogdanovic in 1996. A large number of new complex hydride materials in various forms and combinations have been synthesized and characterized, and the knowledge regarding the properties of complex hydrides and the synthesis methods has grown enormously since then. A significant portion of the research groups active in the field of complex hydrides is collaborators in the International Energy Agreement Task 32. This paper reports about the important issues in the field of complex hydride research, i.e. the synthesis of borohydrides, the thermodynamics of complex hydrides, the effects of size and confinement, the hydrogen sorption mechanism and the complex hydride composites as well as the properties of liquid complex hydrides. This paper is the result of the collaboration of several groups and is an excellent summary of the recent achievements.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-286626 (URN)10.1007/s00339-016-9881-5 (DOI)000372259900094 ()
Available from: 2016-04-28 Created: 2016-04-21 Last updated: 2017-11-30Bibliographically approved
Thersleff, T., Rusz, J., Hjörvarsson, B. & Leifer, K. (2016). Detection of magnetic circular dichroism with subnanometer convergent electron beams. Physical Review B, 94(13), Article ID 134430.
Open this publication in new window or tab >>Detection of magnetic circular dichroism with subnanometer convergent electron beams
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 13, article id 134430Article in journal (Refereed) Published
Abstract [en]

The electron energy-loss spectroscopy technique known as electron magnetic circular dichroism (EMCD) has enormous potential for quantitatively probing the magnetic behavior of materials on the nanoscale. However, the requirement for mostly parallel illumination conditions greatly complicates the extraction of EMCD signals from surface areas under a few square nanometers, because scanning probe methods are limited to around this spatial resolution by the need for higher convergence angles. Here we propose theoretically and demonstrate experimentally that EMCD detection is feasible with convergence angles that are sufficiently large even for atomic resolution spectroscopy. Utilizing scanning transmission electron microscopy we experimentally detect a clear EMCD signal from a 50-nm-thick sample of bcc iron using a convergence semiangle of 8 mrad at 300 keV acceleration voltage, resulting in a probe size of approximately 2 angstrom. We subsequently estimate the number of chirally scattered electrons needed for an unambiguous detection of the EMCD signal and present a method to quantify confidence in signal detection.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-308916 (URN)10.1103/PhysRevB.94.134430 (DOI)000387015900003 ()
Funder
Swedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2009-2017
Available from: 2016-12-01 Created: 2016-12-01 Last updated: 2017-11-29Bibliographically approved
Moubah, R., Magnus, F., Warnatz, T., Pálsson, G. K., Kapaklis, V., Ukleev, V., . . . Hjörvarsson, B. (2016). Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices. Physical Review Applied, 5(4), Article ID 044011.
Open this publication in new window or tab >>Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices
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2016 (English)In: Physical Review Applied, E-ISSN 2331-7019, Vol. 5, no 4, article id 044011Article in journal (Refereed) Published
Abstract [en]

We report on a discrete layer-by-layer magnetic switching in Fe/MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-297910 (URN)10.1103/PhysRevApplied.5.044011 (DOI)000374562100001 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2016-06-29 Created: 2016-06-28 Last updated: 2018-07-02Bibliographically approved
Moubah, R., Boutahar, A., Lassri, H., Dinia, A., Colis, S., Hjörvarsson, B. & Jönsson, P. (2016). Enhanced magnetocaloric properties of FeZr amorphous films by C ion implantation. Materials letters (General ed.), 175, 5-8
Open this publication in new window or tab >>Enhanced magnetocaloric properties of FeZr amorphous films by C ion implantation
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2016 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 175, p. 5-8Article in journal (Refereed) Published
Abstract [en]

For a high magnetic refrigeration efficiency, a large change of magnetic entropy (-Delta S-M) associated with a high relative cooling power (RCP) are highly desirable. Here, the ion implantation is used to enhance both parameters in FeZr amorphous films. A considerable enhancement of both (-Delta S-M) and RCP, from 0.66 to 1.01 J/kg K and 84.5 to 155.5 J/kg respectively, for the as-grown sample compared to the C -implanted sample is obtained for a magnetic field change of mu(0)Delta H = 1.5 T. The increase of (-Delta S-M) and RCP values, are attributed to the increase of the magnetization and the chemical inhomogeneity, respectively upon C implantation.

Keywords
Magnetocaloric materials, Thin films, Relative cooling power, Magnetic entropy, Ion implantation
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-298050 (URN)10.1016/j.matlet.2016.03.124 (DOI)000375851200002 ()
Funder
Swedish Research Council
Available from: 2016-07-06 Created: 2016-06-29 Last updated: 2017-11-28Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1803-9467

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