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  • 1.
    Busch, Christian
    et al.
    Applied Physical Chemistry, Institute for Physical Chemistry, Heidelberg University, Heidelberg, Germany.
    Nagy, Bela
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Stöcklin, Andreas
    Applied Physical Chemistry, Institute for Physical Chemistry, Heidelberg University, Heidelberg, Germany.
    Gutfreund, Philipp
    Institut Laue-Langevin, France.
    Dahint, Reiner
    Applied Physical Chemistry, Institute for Physical Chemistry, Heidelberg University, Heidelberg, Germany.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    A mobile setup for simultaneous and in situ neutron reflectivity, infrared spectroscopy, and ellipsometry studies2022In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 93, no 11Article in journal (Refereed)
    Abstract [en]

    Neutron reflectivity at the solid/liquid interface offers unique opportunities for resolving the structure–function relationships of interfacial layers in soft matter science. It is a non-destructive technique for detailed analysis of layered structures on molecular length scales, providing thickness, density, roughness, and composition of individual layers or components of adsorbed films. However, there are also some well-known limitations of this method, such as the lack of chemical information, the difficulties in determining large layer thicknesses, and the limited time resolution. We have addressed these shortcomings by designing and implementing a portable sample environment for in situ characterization at neutron reflectometry beamlines, integrating infrared spectroscopy under attenuated total reflection for determination of molecular entities and their conformation, and spectroscopic ellipsometry for rapid and independent measurement of layer thicknesses and refractive indices. The utility of this combined setup is demonstrated by two projects investigating (a) pH-dependent swelling of polyelectrolyte layers and (b) the impact of nanoparticles on lipid membranes to identify potential mechanisms of nanotoxicity. 

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  • 2. Order onlineBuy this publication >>
    Nagy, Bela
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Neutron Reflectometry Studies of the Hydrated Structure of Polymer Thin Films2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Polymer coatings are inexpensive surface modifications providing a wide variety of functions. There is an ever-present motivation to improve the films’ performance and to decrease the cost and the environmental footprint of their production. This thesis includes the study of the structural and functional parameters of polymer coatings that are aimed at preventing biological fouling, the unwanted attachment of organic molecules and organisms on surfaces. The focus was on thin films prepared by the self-initiated photografting and photopolymerization method. This is a UV-initiated polymerization reaction that does not require additional chemicals beyond the monomers and the solvent. Since biofouling is a prominent problem in wet environments, the emphasis was placed on the hydrated structure of the films. Neutron reflectometry was selected as a primary method for these studies, since it is a powerful method for investigating the structure of polymer thin films, especially in the hydrated state due to the labelling offered by isotope substitution. This allows the determination of the solvent volume fraction depth profile, which reveals the chain segment density profile in the hydrated film. To resolve fast changes in the film structure and to study the chemical composition, spectroscopic ellipsometry and infrared absorption spectroscopy was implemented in a setup for in-situ measurements in parallel with neutron reflectometry.  

    This thesis contains an introduction and five research articles, and it can be divided into two main parts: the first focusing on the polymerization reaction and the resulting polymer films and the second on the reflectivity method and instrumentation development. Firstly, uncharged hydrophilic polymer layers were prepared by self-initiated photografting and photopolymerization and the hydrated structure of these was investigated. It was found that the films follow a stretched profile indicating negligible crosslinking, and that the growth dynamics is determined by the balance of grafting and removal through radiation damage. Studying sequential grafting of oppositely charged polyelectrolytes confirmed the results on growth dynamics and showed the effects of electrostatic interactions between the monomers. This also demonstrated that the polymerization method is ill suited for preparing block co-polymers due to the removal of material from the previous layer. However, these studies also show that the growth of the second layer tends to proceed from the substrate, forming a system where the two kinds of chains co-exist and interact in the same layer. The grafting of random co-polymers was also investigated by comparing the anti-fouling performance of layers made from a mixture of oppositely charged monomers to layers made using zwitterionic polymers, resulting in no significant difference. This was attributed to the pairwise deposition of oppositely charged monomers, further emphasizing the importance of the Coulomb force in defining the structure of the charged films. The second part of this work focuses on instrument development. Here the building and testing of an angle-dispersive reflectometer is presented, and the design and first applications of an in-situ setup for measuring spectroscopic ellipsometry and infrared spectroscopy along with neutron reflectometry is described. 

    By investigating the structure of the polymer films prepared by self-initiated photografting and photopolymerization, this work improved the understanding of this method, facilitating the development of new applications in the future. By combining additional methods with neutron reflectometry, both fast changes in the structure and the chemical evolution of the samples can be investigated. However, the differences in the sensitivities and the structural models required by the probes present new challenges in modelling. 

    List of papers
    1. Structure and pH-Induced Swelling of Polymer Films Prepared from Sequentially Grafted Polyelectrolytes
    Open this publication in new window or tab >>Structure and pH-Induced Swelling of Polymer Films Prepared from Sequentially Grafted Polyelectrolytes
    2022 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 38, no 5, p. 1725-1737Article in journal (Refereed) Published
    Abstract [en]

    We have prepared a series of ampholytic polymer films, using a self-initiated photografting and photopolymerization (SI-PGP) method to sequentially polymerize first anionic (deuterated methacrylic acid (dMAA)) and thereafter cationic (2-aminoethyl methacrylate (AEMA)) monomers to investigate the SI-PGP grafting process. Dry films were investigated by ellipsometry, X-ray, and neutron reflectometry, and their swelling was followed over a pH range from 4.5 to 10.5 with spectroscopic ellipsometry. The deuterated monomer allows us to separate the distributions of the two components by neutron reflectometry. Growth of both polymers proceeds via grafting of solution-polymerized fragments to the surface, and also the second layer is primarily grafted to the substrate and not as a continuation of the existing chains. The polymer films are stratified, with one layer of near 1:1 composition and the other layer enriched in one component and located either above or below the former layer. The ellipsometry results show swelling transitions at low and high pH but with no systematic variation in the pH values where these transitions occur. The results suggest that grafting density in SI-PGP-prepared homopolymers could be increased via repeated polymerization steps, but that this process does not necessarily increase the average chain length.

    Place, publisher, year, edition, pages
    American Chemical Society (ACS), 2022
    National Category
    Polymer Chemistry
    Identifiers
    urn:nbn:se:liu:diva-183922 (URN)10.1021/acs.langmuir.1c02784 (DOI)000763586100009 ()35081310 (PubMedID)
    Note

    Funding Agencies|Swedish Research Council (Vetenskapsradet)Swedish Research Council [2014-4004]; Swedish Research Council (Rontgen-Angstrom grant, Vetenskapsradet) [2017-06696]; German Research Foundation (Deutsche Forschungsgemeinschaft, DFG)German Research Foundation (DFG) [107745057-TRR80]

    Available from: 2022-04-01 Created: 2022-04-01 Last updated: 2023-12-28
    2. Structure of Self-Initiated Photopolymerized Films: A Comparison of Models
    Open this publication in new window or tab >>Structure of Self-Initiated Photopolymerized Films: A Comparison of Models
    2022 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 38, no 45, p. 14004-14015Article in journal (Refereed) Published
    Abstract [en]

    Self-initiated photografting and photopolymerization (SI-PGP) uses UV illumination to graft polymers to surfaces without additional photoinitiators using the monomers as initiators, “inimers”. A wider use of this method is obstructed by a lack of understanding of the resulting, presumably heterogeneous, polymer structure and of the parallel degradation under continuous UV illumination. We have used neutron reflectometry to investigate the structure of hydrated SI-PGP-prepared poly(HEMA-co-PEG10MA) (poly(2-hydroxyethyl methacrylate-co-(ethylene glycol)10 methacrylate)) films and compared parabolic, sigmoidal, and Gaussian models for the polymer volume fraction distributions. Results from fitting these models to the data suggest that either model can be used to approximate the volume fraction profile to similar accuracy. In addition, a second layer of deuterated poly(methacrylic acid) (poly(dMAA)) was grafted over the existing poly(HEMA-co-PEG10MA) layer, and the resulting double-grafted films were also studied by neutron reflectometry to shed light on the UV-polymerization process and the inevitable UV-induced degradation which competes with the grafting.

    Place, publisher, year, edition, pages
    American Chemical Society, 2022
    National Category
    Polymer Chemistry
    Identifiers
    urn:nbn:se:liu:diva-190018 (URN)10.1021/acs.langmuir.2c02396 (DOI)000881133700001 ()
    Funder
    Swedish Research Council, 2014-04004; 2017-06696
    Available from: 2022-11-17 Created: 2022-11-17 Last updated: 2023-12-28Bibliographically approved
    3. Polyampholytic Poly(AEMA-co-SPMA) Thin Films and Their Potential for Antifouling Applications
    Open this publication in new window or tab >>Polyampholytic Poly(AEMA-co-SPMA) Thin Films and Their Potential for Antifouling Applications
    Show others...
    2021 (English)In: ACS Applied Polymer Materials, ISSN 2637-6105, Vol. 3, no 11, p. 5361-5372Article in journal (Refereed) Published
    Abstract [en]

    Polyampholytic poly(2-aminoethyl methacrylate-co-sulfopropyl methacrylate) (p(AEMA-co-SPMA)) thin films were prepared by self-initiated photopolymerization and photografting (SIPGP) and are demonstrated to be a potential alternative to films prepared from zwitterionic poly(sulfobetaine methacrylate) (pSBMA) for antifouling applications. SIPGP allows polymerization from aqueous solutions containing only monomers, implying that p(AEMA-co-SPMA) thin films can be prepared simply and inexpensively without the risk of introducing potentially toxic substances necessary in many controlled polymerization reactions. For the polymers, wettabilities were studied by contact angle goniometry, the compositions of the films were determined by infrared and X-ray photoelectron spectroscopies, and streaming current measurements were used to assess their net charge. The antibiofouling properties were compared via adsorption of fibrinogen and bovine serum albumin, settlement of algal zoospores, and the growth of sporelings of the marine alga Ulva lactuca. The fouling of the p(AEMA-co-SPMA) copolymer was in several respects similar to that of the zwitterionic pSBMA and suggests that it is potentially suitable for applications under high-salinity conditions, such as marine or physiological environments.

    Place, publisher, year, edition, pages
    American Chemical Society (ACS), 2021
    Keywords
    self-initiated photopolymerization and photografting; polyampholyte; poly(AEMA-co-SPMA); protein adsorption; marine biofouling; spore settlement; Ulva lactuca
    National Category
    Polymer Chemistry
    Identifiers
    urn:nbn:se:liu:diva-181682 (URN)10.1021/acsapm.1c00383 (DOI)000719860800004 ()
    Note

    Funding Agencies|European Communitys Seventh Framework Program FP7/2007-2013 [237997]; Swedish Research Council (VR)Swedish Research Council [2014-04004, 2017-06696, 621-2013-5357]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Carl Tryggers Stiftelse [CTS 15:507]

    Available from: 2021-12-07 Created: 2021-12-07 Last updated: 2023-12-28
    4. A mobile setup for simultaneous and in situ neutron reflectivity, infrared spectroscopy, and ellipsometry studies
    Open this publication in new window or tab >>A mobile setup for simultaneous and in situ neutron reflectivity, infrared spectroscopy, and ellipsometry studies
    Show others...
    2022 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 93, no 11Article in journal (Refereed) Published
    Abstract [en]

    Neutron reflectivity at the solid/liquid interface offers unique opportunities for resolving the structure–function relationships of interfacial layers in soft matter science. It is a non-destructive technique for detailed analysis of layered structures on molecular length scales, providing thickness, density, roughness, and composition of individual layers or components of adsorbed films. However, there are also some well-known limitations of this method, such as the lack of chemical information, the difficulties in determining large layer thicknesses, and the limited time resolution. We have addressed these shortcomings by designing and implementing a portable sample environment for in situ characterization at neutron reflectometry beamlines, integrating infrared spectroscopy under attenuated total reflection for determination of molecular entities and their conformation, and spectroscopic ellipsometry for rapid and independent measurement of layer thicknesses and refractive indices. The utility of this combined setup is demonstrated by two projects investigating (a) pH-dependent swelling of polyelectrolyte layers and (b) the impact of nanoparticles on lipid membranes to identify potential mechanisms of nanotoxicity. 

    Place, publisher, year, edition, pages
    American Institute of Physics, 2022
    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:liu:diva-190021 (URN)10.1063/5.0118329 (DOI)000936778000014 ()36461462 (PubMedID)
    Note

    Funding agencies: Rontgen-Angstrom grant (Vetenskapsradet) [VR 2017-06696]; Rontgen-Angstrom grant (BMBF) [05K18VHA]; Swedish Research Council (Vetenskapsradet) [2014-4004]

    Available from: 2022-11-17 Created: 2022-11-17 Last updated: 2023-12-28Bibliographically approved
    5. GINA—A polarized neutron reflectometer at the Budapest Neutron Centre
    Open this publication in new window or tab >>GINA—A polarized neutron reflectometer at the Budapest Neutron Centre
    Show others...
    2013 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 84, no 1Article in journal (Refereed) Published
    Abstract [en]

    The setup, capabilities, and operation parameters of the neutron reflectometer GINA, the recently installed “Grazing Incidence Neutron Apparatus” at the Budapest Neutron Centre, are introduced. GINA, a dance-floor-type, constant-energy, angle-dispersive reflectometer is equipped with a 2D position-sensitive detector to study specular and off-specular scattering. Wavelength options between 3.2 and 5.7 Å are available for unpolarized and polarized neutrons. Spin polarization and analysis are achieved by magnetized transmission supermirrors and radio-frequency adiabatic spin flippers. As a result of vertical focusing by a five-element pyrolytic graphite monochromator, the reflected intensity from a 20 × 20 mm2 sample has been doubled. GINA is dedicated to studies of magnetic films and heterostructures, but unpolarized options for non-magnetic films, membranes, and other surfaces are also provided. Shortly after its startup, reflectivity values as low as 3 × 10−5 have been measured by the instrument. The instrument capabilities are demonstrated by a non-polarized and a polarized reflectivity experiment on a Si wafer and on a magnetic film of [62Ni/natNi]5 isotope-periodic layer composition. The facility is now open for the international user community. Its further development is underway establishing new sample environment options and spin analysis of off-specularly scattered radiation as well as further decreasing the background.

    Place, publisher, year, edition, pages
    American Institute of Physics, 2013
    National Category
    Accelerator Physics and Instrumentation
    Identifiers
    urn:nbn:se:liu:diva-189396 (URN)10.1063/1.4770129 (DOI)
    Note

    Funding agencies: This work was partially supported by the National Office for Research and Technology of Hungary and the Hungarian National Science Fund (OTKA) under contracts NAP-VENEUS'05 and K 62272, respectively. Mobility support for A. V. Petrenko by the bilateral project between JINR (Dubna) and the Hungarian Academy of Sciences is gratefully appreciated.

    Available from: 2022-10-19 Created: 2022-10-19 Last updated: 2023-12-28Bibliographically approved
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  • 3.
    Nagy, Bela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Campana, Mario
    STFC, England.
    Khaydukov, Yury N.
    Max Planck Inst Festkorpetforsch, Germany; Heinz Maier Leibnitz Zentrum MLZ, Germany.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Structure and pH-Induced Swelling of Polymer Films Prepared from Sequentially Grafted Polyelectrolytes2022In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 38, no 5, p. 1725-1737Article in journal (Refereed)
    Abstract [en]

    We have prepared a series of ampholytic polymer films, using a self-initiated photografting and photopolymerization (SI-PGP) method to sequentially polymerize first anionic (deuterated methacrylic acid (dMAA)) and thereafter cationic (2-aminoethyl methacrylate (AEMA)) monomers to investigate the SI-PGP grafting process. Dry films were investigated by ellipsometry, X-ray, and neutron reflectometry, and their swelling was followed over a pH range from 4.5 to 10.5 with spectroscopic ellipsometry. The deuterated monomer allows us to separate the distributions of the two components by neutron reflectometry. Growth of both polymers proceeds via grafting of solution-polymerized fragments to the surface, and also the second layer is primarily grafted to the substrate and not as a continuation of the existing chains. The polymer films are stratified, with one layer of near 1:1 composition and the other layer enriched in one component and located either above or below the former layer. The ellipsometry results show swelling transitions at low and high pH but with no systematic variation in the pH values where these transitions occur. The results suggest that grafting density in SI-PGP-prepared homopolymers could be increased via repeated polymerization steps, but that this process does not necessarily increase the average chain length.

    Download full text (pdf)
    fulltext
  • 4.
    Nagy, Bela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Ekblad, Tobias
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Fragneto, Giovanna
    Institut Laue-Langevin, Grenoble, France.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Structure of Self-Initiated Photopolymerized Films: A Comparison of Models2022In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 38, no 45, p. 14004-14015Article in journal (Refereed)
    Abstract [en]

    Self-initiated photografting and photopolymerization (SI-PGP) uses UV illumination to graft polymers to surfaces without additional photoinitiators using the monomers as initiators, “inimers”. A wider use of this method is obstructed by a lack of understanding of the resulting, presumably heterogeneous, polymer structure and of the parallel degradation under continuous UV illumination. We have used neutron reflectometry to investigate the structure of hydrated SI-PGP-prepared poly(HEMA-co-PEG10MA) (poly(2-hydroxyethyl methacrylate-co-(ethylene glycol)10 methacrylate)) films and compared parabolic, sigmoidal, and Gaussian models for the polymer volume fraction distributions. Results from fitting these models to the data suggest that either model can be used to approximate the volume fraction profile to similar accuracy. In addition, a second layer of deuterated poly(methacrylic acid) (poly(dMAA)) was grafted over the existing poly(HEMA-co-PEG10MA) layer, and the resulting double-grafted films were also studied by neutron reflectometry to shed light on the UV-polymerization process and the inevitable UV-induced degradation which competes with the grafting.

    Download full text (pdf)
    fulltext
  • 5.
    Yandi, Wetra
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Nagy, Bela
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Skallberg, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Zimmermann, Ralf
    Max Bergmann Ctr Biomat Dresden, Germany.
    Liedberg, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering. Nanyang Technol Univ, Singapore.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Polyampholytic Poly(AEMA-co-SPMA) Thin Films and Their Potential for Antifouling Applications2021In: ACS Applied Polymer Materials, ISSN 2637-6105, Vol. 3, no 11, p. 5361-5372Article in journal (Refereed)
    Abstract [en]

    Polyampholytic poly(2-aminoethyl methacrylate-co-sulfopropyl methacrylate) (p(AEMA-co-SPMA)) thin films were prepared by self-initiated photopolymerization and photografting (SIPGP) and are demonstrated to be a potential alternative to films prepared from zwitterionic poly(sulfobetaine methacrylate) (pSBMA) for antifouling applications. SIPGP allows polymerization from aqueous solutions containing only monomers, implying that p(AEMA-co-SPMA) thin films can be prepared simply and inexpensively without the risk of introducing potentially toxic substances necessary in many controlled polymerization reactions. For the polymers, wettabilities were studied by contact angle goniometry, the compositions of the films were determined by infrared and X-ray photoelectron spectroscopies, and streaming current measurements were used to assess their net charge. The antibiofouling properties were compared via adsorption of fibrinogen and bovine serum albumin, settlement of algal zoospores, and the growth of sporelings of the marine alga Ulva lactuca. The fouling of the p(AEMA-co-SPMA) copolymer was in several respects similar to that of the zwitterionic pSBMA and suggests that it is potentially suitable for applications under high-salinity conditions, such as marine or physiological environments.

    Download full text (pdf)
    fulltext
  • 6.
    Nagy, Bela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering. Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary.
    Merkel, D. G.
    Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary.
    Jakab, L.
    Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary.
    Fuzi, J.
    Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary.
    Veres, T.
    Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary.
    Bottyan, L.
    Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary.
    4-bounce neutron polarizer for reflectometry applications2018In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, no 5, article id 056105Article in journal (Refereed)
    Abstract [en]

    A neutron polarizer using four successive reflections on m = 2.5 supermirrors was built and installed at the GINA neutron reflectometer at the Budapest Neutron Centre. This simple setup exhibits 99.6% polarizing efficiency with 80% transmitted intensity of the selected polarization state. Due to the geometry, the higher harmonics in the incident beam are filtered out, while the optical axis of the beam remains intact for easy mounting and dismounting the device in an existing experimental setup. Published by AIP Publishing.

  • 7.
    Nagy, Bela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering. Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary.
    Khaydukov, Yu.
    Max-Planck Institute for Solid State Research, Stuttgart, Germany; Max Planck Society Outstation at FRM-II, Garching, Germany; Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia.
    Efremov, D.
    Max Planck Institute Solid State Research, Germany; Leibniz Institute Solid State and Mat Research Dresden, Germany.
    Vasenko, A. S.
    National Research University Higher School of Economics, Moscow, Russia.
    Mustafa, L.
    Max-Planck Institute for Solid State Research, Stuttgart, Germany.
    Kim, J. -H.
    Max Planck Institute Solid State Research, Germany.
    Keller, T.
    Max Planck Institute Solid State Research, Germany; Max Planck Soc Outstn FRM II, Germany.
    Zhernenkov, K.
    Ruhr University of Bochum, Germany.
    Devishvili, A.
    Ruhr University of Bochum, Germany; Division of Physical Chemistry, Department of Chemistry, Lund University, Lund, Sweden.
    Steitz, R.
    Helmholtz-Zentrum für Materialien und Energie, Berlin, Germany.
    Keimer, B.
    Max Planck Institute Solid State Research, Germany.
    Bottyan, L.
    Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary.
    On the explanation of the paramagnetic Meissner effect in superconductor/ferromagnet heterostructures2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 116, no 1, article id 17005Article in journal (Refereed)
    Abstract [en]

    An increase of the magnetic moment in superconductor/ferromagnet (S/F) bilayers V(40 nm)/F (F = Fe(1, 3 nm), Co(3 nm), Ni(3 nm)) was observed using SQUID magnetometry upon cooling below the superconducting transition temperature TC in magnetic fields of 10 Oe to 50 Oe applied parallel to the sample surface. A similar increase, often called the paramagnetic Meissner effect (PME), was observed before in various superconductors and superconductor/ferromagnet systems. To explain the PME effect in the presented S/F bilayers a model based on a row of vortices located at the S/F interface is proposed. According to the model the magnetic moment induced below TC consists of the paramagnetic contribution of the vortex cores and the diamagnetic contribution of the vortex-free region of the S layer. Since the thickness of the S layer is found to be 3-4 times less than the magnetic-field penetration depth, this latter diamagnetic contribution is negligible. The model correctly accounts for the sign, the approximate magnitude and the field dependence of the paramagnetic and the Meissner contributions of the induced magnetic moment upon passing the superconducting transition of a ferromagnet/superconductor bilayer. Copyright (C) EPLA, 2016.

  • 8.
    Bottyán, L.
    et al.
    Wigner RCP, RMKI, Budapest, Hungary.
    Merkel, D. G.
    Wigner RCP, RMKI, Budapest, Hungary.
    Nagy, Bela
    Wigner RCP, RMKI, Budapest, Hungary.
    Füzi, J.
    Wigner RCP, SZFKI, Budapest, Hungary; Pollack Mihaly Faculty of Engineering and Information Technology, University of Pécs, Pécs, Hungary.
    Sajti, Sz.
    Wigner RCP, RMKI, Budapest, Hungary.
    Deák, L.
    Wigner RCP, RMKI, Budapest, Hungary.
    Endrőczi, G.
    Wigner RCP, RMKI, Budapest, Hungary.
    Petrenko, A. V.
    Frank Laboratory of Neutron Physics, JINR, Dubna, Russia.
    Major, J.
    Wigner RCP, RMKI, Budapest, Hungary; Max-Planck-Institut für Intelligente Systeme (formerly Max-Planck-Institut für Metallforschung), Stuttgart, Germany.
    GINA—A polarized neutron reflectometer at the Budapest Neutron Centre2013In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 84, no 1Article in journal (Refereed)
    Abstract [en]

    The setup, capabilities, and operation parameters of the neutron reflectometer GINA, the recently installed “Grazing Incidence Neutron Apparatus” at the Budapest Neutron Centre, are introduced. GINA, a dance-floor-type, constant-energy, angle-dispersive reflectometer is equipped with a 2D position-sensitive detector to study specular and off-specular scattering. Wavelength options between 3.2 and 5.7 Å are available for unpolarized and polarized neutrons. Spin polarization and analysis are achieved by magnetized transmission supermirrors and radio-frequency adiabatic spin flippers. As a result of vertical focusing by a five-element pyrolytic graphite monochromator, the reflected intensity from a 20 × 20 mm2 sample has been doubled. GINA is dedicated to studies of magnetic films and heterostructures, but unpolarized options for non-magnetic films, membranes, and other surfaces are also provided. Shortly after its startup, reflectivity values as low as 3 × 10−5 have been measured by the instrument. The instrument capabilities are demonstrated by a non-polarized and a polarized reflectivity experiment on a Si wafer and on a magnetic film of [62Ni/natNi]5 isotope-periodic layer composition. The facility is now open for the international user community. Its further development is underway establishing new sample environment options and spin analysis of off-specularly scattered radiation as well as further decreasing the background.

  • 9.
    Khaydukov, Yu. N.
    et al.
    Moscow State University, Moscow, Russia / Joint Institute for Nuclear Research, Dubna, Russia.
    Aksenov, V. L.
    Joint Institute for Nuclear Research, Dubna, Russia.
    Nikitenko, Yu. V.
    Joint Institute for Nuclear Research, Dubna, Russia.
    Zhernenkov, K. N.
    Joint Institute for Nuclear Research, Dubna, Russia / Ruhr-Universität Bochum, Bochum, Germany.
    Nagy, Bela
    KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary.
    Teichert, A.
    Helmholtz-Zentrum für Materialien und Energie, Berlin, Germany / Instituut voor Kern-en Stralings fysica and INPA, CLeuven, Belgium.
    Steitz, R.
    Helmholtz-Zentrum für Materialien und Energie, Berlin, Germany.
    Rühm, A.
    Max-Planck-Institut für Metallforschung, Stuttgart, Germany.
    Bottyán, L.
    KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary.
    Magnetic Proximity Effects in V/Fe Superconductor/Ferromagnet Single Bilayer Revealed by Waveguide-Enhanced Polarized Neutron Reflectometry2011In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 24, no 1-2, p. 961-968Article in journal (Refereed)
    Abstract [en]

    Polarized neutron reflectometry is used to study the magnetic proximity effect in a superconductor/ferromagnet (SC/FM) system of composition Cu(32 nm)/ V(40 nm)/Fe(1 nm)/MgO. In contrast to previous studies, here a single SC/FM bilayer, is studied and multilayer artefacts are excluded. The necessary signal enhancement is achieved by waveguide resonance, i.e., preparing the V(40 nm)/Fe(1 nm) SC/FM bilayer sandwiched by the highly reflective MgO substrate and Cu top layer, respectively. A new magnetic state of the system was observed at temperatures below 0.7TC manifested in a systematic change in the height and width of the waveguide resonance peak. Upon increasing the temperature from 0.7TC to TC, a gradual decay of this state is observed, accompanied by a 5% growth of the diffuse scattering. This behavior can be explained in a natural way by the polarization of the superconducting electrons upon the SC transition, i.e., an appearance of additional induced magnetization within the SC, due to the proximity of the FM layer.

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