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Pálsson, Gunnar K.
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Publications (10 of 51) Show all publications
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
Komander, K., Moro, M. V., Droulias, S. A., Müggenburg, J., Pálsson, G. K., Nyberg, T., . . . Wolff, M. (2019). Hydrogen site location in ultrathin vanadium layers by N-15 nuclear reaction analysis. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 455, 57-60
Open this publication in new window or tab >>Hydrogen site location in ultrathin vanadium layers by N-15 nuclear reaction analysis
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2019 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 455, p. 57-60Article in journal (Refereed) Published
Abstract [en]

We present a method using resonant nuclear reaction analysis combined with optical transmission and heavy-ion Rutherford backscattering spectrometry to study the absorption of hydrogen in single crystalline thin vanadium films. Probing with the resonant H-1(N-15,alpha gamma)C-12 reaction allows for highly resolved hydrogen depth profiling, while measurements along the crystal axes render possible the direct identification of the interstitial site occupancy. First experiments were performed on thin vanadium hydrides in Fe(Cr)/V superlattices revealing differences in site occupancy.

Place, publisher, year, edition, pages
ELSEVIER, 2019
Keywords
NRA, Metal hydride, Site occupancy, Channeling, N-15, Vanadium
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-392120 (URN)10.1016/j.nimb.2019.05.033 (DOI)000477786500010 ()
Funder
Swedish Research Council, 821-2012-5144Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2019-09-06 Created: 2019-09-06 Last updated: 2020-01-08Bibliographically approved
Valldeperas, M., Dabkowska, A. P., Pálsson, G. K., Rogers, S., Mahmoudi, N., Carnerup, A., . . . Nylander, T. (2019). Interfacial properties of lipid sponge-like nanoparticles and the role of stabilizer on particle structure and surface interactions. Soft Matter, 15(10), 2178-2189
Open this publication in new window or tab >>Interfacial properties of lipid sponge-like nanoparticles and the role of stabilizer on particle structure and surface interactions
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2019 (English)In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 15, no 10, p. 2178-2189Article in journal (Refereed) Published
Abstract [en]

The advantage of using nonlamellar lipid liquid crystalline phases has been demonstrated in many applications, such as drug delivery, protein encapsulation and crystallisation. We have recently reported that a mixture of mono-and diglycerides is able to form sponge-like nanoparticles (L-3-NPs) with large enough aqueous pores to encapsulate macromolecules such as proteins. Here we use small angle neutron scattering (SANS) to reveal morphology, structural and chemical composition of these polysorbate 80 (P80) stabilized sponge phase nanoparticles, not previously known. Our results suggest that L-3-NPs have a core-shell sphere structure, with a shell rich in P80. It was also found that even if P80 is mostly located on the surface, it also contributes to the formation of the inner sponge phase structure. An important aspect for the application and colloidal stability of these particles is their interfacial properties. Therefore, the interfacial behaviour of the nanoparticles on hydrophilic silica was revealed by Quartz crystal microbalance with dissipation (QCM-D) and neutron reflectivity (NR). Adsorption experiments reveal the formation of a thin lipid layer, with the dimension corresponding to a lipid bilayer after L-3-NPs are in contact with hydrophilic silica. This suggests that the diglycerol monoleate/ Capmul GMO-50/P80 particles reorganize themselves on this surface, probably due to interactions between P80 head group and SiO2.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-379883 (URN)10.1039/c8sm02634c (DOI)000460596900004 ()30742188 (PubMedID)
Funder
EU, FP7, Seventh Framework Programme
Available from: 2019-03-25 Created: 2019-03-25 Last updated: 2019-03-25Bibliographically approved
Wolff, M., Devishvili, A., Dura, J. A., Adlmann, F., Kitchen, B., Pálsson, G. K., . . . Toperverg, B. P. (2019). Nuclear Spin Incoherent Neutron Scattering from Quantum Well Resonators. Physical Review Letters, 123(1), Article ID 016101.
Open this publication in new window or tab >>Nuclear Spin Incoherent Neutron Scattering from Quantum Well Resonators
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2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 1, article id 016101Article in journal (Refereed) Published
Abstract [en]

We report the detection and quantification of nuclear spin incoherent scattering from hydrogen occupying interstitial sites in a thin film of vanadium. The neutron wave field is enhanced in a quantum resonator with magnetically switchable boundaries. Our results provide a pathway for the study of dynamics at surfaces and in ultrathin films using inelastic and/or quasielastic neutron scattering methods.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-390920 (URN)10.1103/PhysRevLett.123.016101 (DOI)000473311400011 ()
Funder
Swedish Research Council, 2012-05115
Available from: 2019-08-15 Created: 2019-08-15 Last updated: 2019-08-15Bibliographically 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
Adlmann, F., Herbel, J., Korolkovas, A., Bliersbach, A., Toperverg, B., Van Herck, W., . . . Wolff, M. (2018). Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions [Letter to the editor]. Journal of Physics: Condensed Matter, 30, Article ID 165901.
Open this publication in new window or tab >>Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions
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2018 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, article id 165901Article in journal, Letter (Refereed) Published
Abstract [en]

Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Keywords
GISANS, neutrons, interfaces, depth profiling, resolution
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-348219 (URN)10.1088/1361-648X/aab573 (DOI)000428466400001 ()29521272 (PubMedID)
Funder
Swedish Research Council, 2016-04645The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG-2011-2067
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-06-20Bibliographically approved
Keqi, A., Gehlmann, M., Conti, G., Nemsak, S., Rattanachata, A., Minar, J., . . . Fadley, C. S. (2018). Electronic structure of the dilute magnetic semiconductor Ga1-xMnxP from hard x-ray photoelectron spectroscopy and angle-resolved photoemission. Physical Review B, 97(15), Article ID 155149.
Open this publication in new window or tab >>Electronic structure of the dilute magnetic semiconductor Ga1-xMnxP from hard x-ray photoelectron spectroscopy and angle-resolved photoemission
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 15, article id 155149Article in journal (Refereed) Published
Abstract [en]

We have investigated the electronic structure of the dilute magnetic semiconductor (DMS) Ga0.98Mn0.02P and compared it to that of an undoped GaP reference sample, using hard x-ray photoelectron spectroscopy (HXPS) and hard x-ray angle-resolved photoemission spectroscopy (HARPES) at energies of about 3 keV. We present experimental data, as well as theoretical calculations, to understand the role of the Mn dopant in the emergence of ferromagnetism in this material. Both core-level spectra and angle-resolved or angle-integrated valence spectra are discussed. In particular, the HARPES experimental data are compared to free-electron final-state model calculations and to more accurate one-step photoemission theory. The experimental results show differences between Ga0.98Mn0.02P and GaP in both angle-resolved and angle-integrated valence spectra. The Ga0.98Mn0.02P bands are broadened due to the presence of Mn impurities that disturb the long-range translational order of the host GaP crystal. Mn-induced changes of the electronic structure are observed over the entire valence band range, including the presence of a distinct impurity band close to the valence-band maximum of the DMS. These experimental results are in good agreement with the one-step photoemission calculations and a prior HARPES study of Ga0.97Mn0.03As and GaAs [Gray et al., Nat. Mater. 11, 957 (2012)], demonstrating the strong similarity between these two materials. The Mn 2p and 3s core-level spectra also reveal an essentially identical state in doping both GaAs and GaP.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-354111 (URN)10.1103/PhysRevB.97.155149 (DOI)000430545100003 ()
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-06-26Bibliographically approved
Pilkington, G. A., Harris, K., Bergendal, E., Reddy, A. B., Pálsson, G. K., Vorobiev, A., . . . Rutland, M. W. (2018). Electro-responsivity of ionic liquid boundary layers in a polar solvent revealed by neutron reflectance. Journal of Chemical Physics, 148(19), Article ID 193806.
Open this publication in new window or tab >>Electro-responsivity of ionic liquid boundary layers in a polar solvent revealed by neutron reflectance
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2018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 19, article id 193806Article in journal (Refereed) Published
Abstract [en]

Using neutron reflectivity, the electro-responsive structuring of the non-halogenated ionic liquid (IL) trihexyl(tetradecyl)phosphonium-bis(mandelato)borate, [ P-6,P-6,P-6,P-14][BMB], has been studied at a gold electrode surface in a polar solvent. For a 20% w/w IL mixture, contrast matched to the gold surface, distinct Kiessig fringes were observed for all potentials studied, indicative of a boundary layer of different composition to that of the bulk IL-solvent mixture. With applied potential, the amplitudes of the fringes from the gold-boundary layer interface varied systematically. These changes are attributable to the differing ratios of cations and anions in the boundary layer, leading to a greater or diminished contrast with the gold electrode, depending on the individual ion scattering length densities. Such electro-responsive changes were also evident in the reflectivities measured for the pure IL and a less concentrated (5% w/w) IL-solvent mixture at the same applied potentials, but gave rise to less pronounced changes. These measurements, therefore, demonstrate the enhanced sensitivity achieved by contrast matching the bulk solution and that the structure of the IL boundary layers formed in mixtures is strongly influenced by the bulk concentration. Together these results represent an important step in characterising IL boundary layers in IL-solvent mixtures and provide clear evidence of electro-responsive structuring of IL ions in their solutions with applied potential.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-357749 (URN)10.1063/1.5001551 (DOI)000432853800010 ()
Funder
Knut and Alice Wallenberg Foundation, KAW2012.0078Swedish Research Council, 20144694
Available from: 2018-08-22 Created: 2018-08-22 Last updated: 2018-08-22Bibliographically approved
Nouhi, S., Ahrens, L., Campos Pereira, H., Hughes, A., Campana, M., Gutfreund, P., . . . Hellsing, M. S. (2018). Interactions of perfluoroalkyl substances with a phospholipid bilayer studied by neutron reflectometry. Journal of Colloid and Interface Science, 511, 474-481
Open this publication in new window or tab >>Interactions of perfluoroalkyl substances with a phospholipid bilayer studied by neutron reflectometry
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2018 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 511, p. 474-481Article in journal (Refereed) Published
Abstract [en]

The interactions between perfluoroalkyl substances (PFASs) and a phospholipid bilayer (1,2-dimyristoyl-sn-glycero-3-phosphocholine) were investigated at the molecular level using neutron reflectometry. Representative PFASs with different chain length and functional groups were selected in this study including: perfluorobutane sulfonate (PFBS), perfluorohexanoate (PFHxA), perfluorohexane sulfonate (PFHxS), perfluorononanoate (PFNA), perfluorooctane sulfonate (PFOS), and perfluorooctane sulfonamide (FOSA). All PFASs were found to interact with the bilayer by incorporation, indicating PFAS ability to accumulate once ingested or taken up by organisms. The interactions were observed to increase with chain length and vary with the functional group as SO2NH2" role="presentation">(FOSA) > SO2O−" role="presentation">(PFOS) > COO(PFNA). The PFAS hydrophobicity, which is strongly correlated with perfluorocarbon chain length, was found to strongly influence the interactions. Longer chain PFASs showed higher tendency to penetrate into the bilayer compared to the short-chain compounds. The incorporated PFASs could for all substances but one (PFNA) be removed from the lipid membrane by gentle rinsing with water (2 mL min−1). Although short-chain PFASs have been suggested to be the potentially less bioaccumulative alternative, we found that in high enough concentrations they can also disturb the bilayer. The roughness and disorder of the bilayer was observed to increase as the concentration of PFASs increased (in particular for the high concentrations of short-chain substances i.e. PFHxA and PFBS), which can be an indication of aggregation of PFASs in the bilayer.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-330505 (URN)10.1016/j.jcis.2017.09.102 (DOI)000417008200053 ()29073553 (PubMedID)
Funder
Swedish Research Council, 621-2012-4382Swedish Research Council, 2015-03938
Available from: 2017-10-02 Created: 2017-10-02 Last updated: 2019-06-28Bibliographically approved
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