| 1. |
- Dahlqvist, Martin, et al.
(författare)
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Magnetically driven anisotropic structural changes in the atomic laminate Mn2GaC
- 2016
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 93:1
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Tidskriftsartikel (refereegranskat)abstract
- Inherently layered magnetic materials, such as magnetic M(n+1)AX(n) (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition M(n+1)AX(n) consists of M(n+1)AX(n) blocks separated by atomically thin A-layers where M is a transition metal, A an A-group element, X refers to carbon and/or nitrogen, and n is typically 1, 2, or 3. Here, we show that the recently discovered magnetic Mn2GaC MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of Mn2GaC MAX phases in future magnetoelectric and magnetocaloric applications.
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| 2. |
- Holmin, Susanne, et al.
(författare)
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Corrosion of ruthenium dioxide based cathodes in alkaline medium caused by reverse currents
- 2014
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 146:10, s. 30-36
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Tidskriftsartikel (refereegranskat)abstract
- A reverse current obtained during power shutdowns in industrial processes, such as chlor-alkali production or alkaline water electrolysis, is deleterious for hydrogen evolving ruthenium dioxide (Ru02) based cathodes. It has been observed that RuO2 coatings after a power shutdown, necessary for e.g. maintenance, are severely damaged unless polarization rectifiers are employed. In this work we show why these types of cathodes are sensitive to reverse currents, i.e. anodic currents, after hydrogen evolution. RuO2 coatings deposited on nickel substrates were subjected to different electrochemical treatments such as hydrogen evolution, oxygen evolution, or reverse currents in 8 M NaOH at 90 degrees C. Polarity inversion was introduced after hydrogen evolution to simulate the effect of reverse currents. Because of chemical interaction with hydrogen, a significant amount of the RuO2 coating was transformed into hydroxylated species during cathodic polarization. Our study shows that these hydroxylated phases are highly sensitive to electrochemical corrosion during anodic polarization after extended hydrogen evolution. (C) 2014 Elsevier Ltd. All rights reserved.
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| 3. |
- Ingason, Arni Sigurdur, et al.
(författare)
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A Nanolaminated Magnetic Phase: Mn2GaC
- 2014
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 2:2, s. 89-93
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Tidskriftsartikel (refereegranskat)abstract
- Layered magnetic materials are fascinating from the point of view of fundamental science as well as applications. Discoveries such as giant magnetoresistance (GMR) in magnetic multilayers have revolutionized data storage and magnetic recording, and concurrently initiated the search for new layered magnetic materials. One group of inherently nanolaminated compounds are the so called Mn+1AXn (MAX) phases. Due to the large number of isostructural compositions, researchers are exploring the wide range of interesting properties, and not primarily functionalization through optimization of structural quality. Magnetic MAX phases have been discussed in the literature, though this is hitherto an unreported phenomenon. However, such materials would be highly interesting, based on the attractive and useful properties attained with layered magnetic materials to date. Here we present a new MAX phase, (Cr1–xMnx)2GeC, synthesized as thin film in heteroepitaxial form, showing single crystal material with unprecedented structural MAX phase quality. The material was identified using first-principles calculations to study stability of hypothetical MAX phases, in an eort to identify a potentially magnetic material. The theory predicts a variety of magnetic behavior depending on the Mn concentration and Cr/Mn atomic conguration within the sublattice. The analyzed thin films display a magnetic signal well above room temperature and with partly ferromagnetic ordering. These very promising results open up a field of new layered magnetic materials, with high potential for electronics and spintronics applications.
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| 4. |
- Ingason, Arni Sigurdur, et al.
(författare)
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Long-range antiferromagnetic order in epitaxial Mn2GaC thin films from neutron reflectometry
- 2016
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Ingår i: PHYSICAL REVIEW B. - : AMER PHYSICAL SOC. - 2469-9950. ; 94:2, s. 024416-
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Tidskriftsartikel (refereegranskat)abstract
- The nature of the magnetic structure in magnetic so-called MAX phases is a topic of some controversy. Here we present unpolarized neutron-diffraction data between 3.4 and 290.0 K and momentum transfer between Q = 0.0 and 1.1 angstrom(-1), as well as complementary x-ray-diffraction data on epitaxial thin films of the MAX phase material Mn2GaC. This inherently layered material exhibits neutron-diffraction peaks consistent with long-ranged antiferromagnetic order with a periodicity of two structural unit cells. The magnetic structure is present throughout the measured temperature range. The results are in agreement with first-principles calculations of antiferromagnetic structures for this material where the Mn-C-Mn atomic trilayers are found to be ferromagnetically coupled internally but spin flipped or rotated across the Ga layers. The present findings have significant bearing on the discussion regarding the nature of the magnetic structure in magnetic MAX phases.
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| 5. |
- Ingason, Arni Sigurdur, et al.
(författare)
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Magnetic MAX phases from theory and experiments: a review
- 2016
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Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 28:43, s. 433003-
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Forskningsöversikt (refereegranskat)abstract
- This review presents MAX phases (M is a transition metal, A an A-group element, X is C or N), known for their unique combination of ceramic/metallic properties, as a recently uncovered family of novel magnetic nanolaminates. The first created magnetic MAX phases were predicted through evaluation of phase stability using density functional theory, and subsequently synthesized as heteroepitaxial thin films. All magnetic MAX phases reported to date, in bulk or thin film form, are based on Cr and/or Mn, and they include (Cr,Mn)(2)AlC, (Cr,Mn)(2)GeC, (Cr,Mn)(2)GaC, (Mo,Mn)(2)GaC, (V,Mn)(3)GaC2, Cr2AlC, Cr2GeC and Mn2GaC. A variety of magnetic properties have been found, such as ferromagnetic response well above room temperature and structural changes linked to magnetic anisotropy. In this paper, theoretical as well as experimental work performed on these materials to date is critically reviewed, in terms of methods used, results acquired, and conclusions drawn. Open questions concerning magnetic characteristics are discussed, and an outlook focused on new materials, superstructures, property tailoring and further synthesis and characterization is presented.
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| 6. |
- Ingason, Arni Sigurdur, et al.
(författare)
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Magnetic Self-Organized Atomic Laminate from First Principles and Thin Film Synthesis
- 2013
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110
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Tidskriftsartikel (refereegranskat)abstract
- he first experimental realization of a magnetic Mn+1AXn (MAX) phase, (Cr0.75Mn0.25)2GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent structural quality. This self-organized atomic laminate is based on the well-known Cr2GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.
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| 7. |
- Ingason, Arni Sigurdur, et al.
(författare)
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Toward Structural Optimization of MAX Phases as Epitaxial Thin Films
- 2016
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Ingår i: Materials Research Letters. - : TAYLOR & FRANCIS INC. - 2166-3831. ; 4:3, s. 152-160
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Tidskriftsartikel (refereegranskat)abstract
- Prompted by the increased focus on MAX phase materials and their two-dimensional counterparts MXenes, a brief review of the current state of affairs in the synthesis of MAX phases as epitaxial thin films is given. Current methods for synthesis are discussed and suggestions are given on how to increase the material quality even further as well as arrive at those conditions faster. Samples were prepared to exemplify the most common issues involved with the synthesis, and through suggested paths for resolving these issues we attain samples of a quality beyond what has previously been reported.
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| 8. |
- Karlsson, Linda, et al.
(författare)
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Graphene on graphene formation from PMMA residues during annealing
- 2017
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Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 137, s. 191-194
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Tidskriftsartikel (refereegranskat)abstract
- PMMA is a common support material for transferring graphene between substrates. However, PMMA residues typically remain on the graphene sheet after the transfer process. A high temperature annealing process is commonly applied to reduce the amount of PMMA residues. It is also known that high temperature annealing of PMMA causes the PMMA to graphitize, which has been used as a method to synthesize graphene on metal substrates. In this letter we show the development of additional graphene layers during high temperature annealing, which occurs on a single, clean, graphene sheet. The additional graphene is nucleated from the decomposition products of PMMA residues. (C) 2017 Elsevier Ltd. All rights reserved.
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| 9. |
- Karlsson, Linda, et al.
(författare)
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Residue reduction and intersurface interaction on single graphene sheets
- 2016
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Ingår i: Carbon. - : Pergamon Press. - 0008-6223 .- 1873-3891. ; 100, s. 345-350
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Tidskriftsartikel (refereegranskat)abstract
- Large regions of pristine graphene are essential to applications which rely on the ideal graphene properties. Common methods for transferring chemical vapour deposition grown graphene to suitable substrates leaves metal oxide particles and poly(methyl methacrylate) (PMMA) residues on opposing surfaces, which degrade the properties. A common method to reduce the residues include annealing in vacuum or in argon, however, residues remain on the graphene sheet. The present investigation reports on the metal oxide particle ripening and PMMA decomposition on a single graphene sheet during in-situ annealing up to 1300 degrees C in a transmission electron microscope. It is shown that the PMMA residues are increasingly reduced at elevated temperatures although the reduction is strongly correlated to the metal oxide particle coverage on the opposing graphene surface. This is shown to occur as a consequence of an electrostatic interaction between the residues and that this prevents the establishment of large clean areas. (C) 2016 Elsevier Ltd. All rights reserved.
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| 10. |
- Leosson, K., et al.
(författare)
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Ultra-thin gold films on transparent polymers
- 2013
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Ingår i: Nanophotonics. - : Walter de Gruyter GmbH. - 2192-8614 .- 2192-8606. ; 2:1, s. 3-11
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Tidskriftsartikel (refereegranskat)abstract
- Fabrication of continuous ultra-thin gold films (
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