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  • 1.
    Ahniyaz, Anwar
    et al.
    Stockholm University, Sweden.
    Seisenbaeva, Gulaim A.
    SLU Swedish University of Agricultural Sciences, Sweden.
    Häggström, Lennart
    Uppsala University, Sweden.
    Kamali, Saeed
    Uppsala University, Sweden.
    Kessler, Vadim G.
    SLU Swedish University of Agricultural Sciences, Sweden.
    Nordblad, Per
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Bergström, Lennart
    Stockholm University, Sweden.
    Preparation of iron oxide nanocrystals by surfactant-free or oleic acid-assisted thermal decomposition of a Fe(III) alkoxide2008In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 320, p. 781-787Article in journal (Refereed)
    Abstract [en]

    A new non-hydrolytic, alkoxide-based route was developed to synthesize iron oxide nanocrystals. Surfactant-free thermal decomposition of the iron 2-methoxy-ethoxide precursors results in the formation of uniform iron oxide nanocrystals with an average size of 5.6 nm. Transmission electron microscope study shows that the nanocrystals are protected against aggregation by a repulsive surface layer, probably originating from the alkoxy-alkoxide ligands. Addition of oleic acid resulted in monodisperse nanocrystals with an average size of 4 nm. Mössbauer analysis confirmed that the nanocrystals mainly consisted of maghemite. Analysis of the magnetic hysteresis loop measurements and the zero field and field cooled measurements displayed an excellent fit to established theories for single-domain superparamagnetic nanocrystals and the size of the magnetic domains correlated well to the crystallite size obtained from transmission electron microscope.

  • 2.
    Ahrentorp, F.
    et al.
    RISE, Swedish ICT, Acreo.
    Astalan, A. P.
    Jonasson, Christian
    RISE, Swedish ICT, Acreo.
    Blomgren, J.
    RISE, Swedish ICT, Acreo.
    Qi, B.
    Thompson Mefford, O.
    Yan, M.
    Courtois, J.
    Berret, J. F.
    Fresnais, J.
    Sandre, O.
    Dutz, S.
    Muller, R.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Sensitive High Frequency AC Suceptometry in Magnetic Nanoparticle Applications2010In: AIP Conference Proceedings, Vol. 1311, p. 213-23Article in journal (Refereed)
  • 3.
    Ahrentorp, Fredrik
    et al.
    RISE, Swedish ICT, Acreo.
    Astalan, Andrea
    RISE, Swedish ICT, Acreo.
    Blomgren, Jakob
    RISE, Swedish ICT, Acreo.
    Jonasson, Christian
    RISE, Swedish ICT, Acreo.
    Wetterskog, Erik
    Uppsala University, Sweden.
    Svedlindh, Peter
    Uppsala University, Sweden.
    Lak, Aidin
    Technical University of Braunschweig, Germany.
    Ludwig, Frank
    Technical University of Braunschweig, Germany.
    van Ijzendoorn, Leo J.
    Eindhoven University of Technology, The Netherlands.
    Westphal, Fritz
    Micromod Partikeltechnologie GmbH, Germany.
    Gruttner, Cordula
    Micromod Partikeltechnologie GmbH, Germany.
    Gehrke, Nicole
    nanoPET Pharma GmbH, Germany.
    Gustafsson, Stefan
    Chalmers University of Technology, Sweden.
    Olsson, Eva
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Effective particle magnetic moment of multi-core particles2015In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 380, p. 221-226Article in journal (Refereed)
    Abstract [en]

    In this study we investigate the magnetic behavior of magnetic multi-core particles and the differences in the magnetic properties of multi-core and single-core nanoparticles and correlate the results with the nanostructure of the different particles as determined from transmission electron microscopy(TEM). We also investigate how the effective particle magnetic moment is coupled to the individual moments of the single-domain nanocrystals by using different measurement techniques: DC magnetometry, AC susceptometry, dynamic light scattering and TEM. We have studied two magnetic multi-core particle systems – BNF Starch from Micromod with a median particle diameter of 100 nm and FeraSpin R from nanoPET with a median particle diameter of 70 nm – and one single-core particle system – SHP25 from Ocean NanoTech with a median particle core diameter of 25 nm.

  • 4.
    Ahrentorp, Fredrik
    et al.
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Blomgren, Jakob
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Jonasson, Christian
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Sarwe, Anna
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Sepehri, Sobhan
    Chalmers University of Technology, Sweden.
    Eriksson, Emil
    Chalmers University of Technology, Sweden.
    Kalaboukhov, Alexei
    Chalmers University of Technology, Sweden.
    Jesorka, Aldo
    Chalmers University of Technology, Sweden.
    Winkler, Dag
    Chalmers University of Technology, Sweden.
    Schneiderman, Justin F.
    University of Gothenburg, Sweden.
    Nilsson, Mats
    Stockholm University, Sweden.
    Albert, Jan
    Karolinska University Hospital, Sweden; Karolinska Institute, Sweden.
    de la Torre, Theresa Z. G.
    Uppsala University, Sweden.
    Strømme, Maria
    Uppsala University, Sweden.
    Johansson, Christer
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Sensitive magnetic biodetection using magnetic multi-core nanoparticles and RCA coils2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 427, p. 14-18Article in journal (Refereed)
    Abstract [en]

    We use functionalized iron oxide magnetic multi-core particles of 100 nm in size (hydrodynamic particle diameter) and AC susceptometry (ACS) methods to measure the binding reactions between the magnetic nanoparticles (MNPs) and bio-analyte products produced from DNA segments using the rolling circle amplification (RCA) method. We use sensitive induction detection techniques in order to measure the ACS response. The DNA is amplified via RCA to generate RCA coils with a specific size that is dependent on the amplification time. After about 75 min of amplification we obtain an average RCA coil diameter of about 1 µm. We determine a theoretical limit of detection (LOD) in the range of 11 attomole (corresponding to an analyte concentration of 55 fM for a sample volume of 200 µL) from the ACS dynamic response after the MNPs have bound to the RCA coils and the measured ACS readout noise. We also discuss further possible improvements of the LOD.

  • 5.
    Andersson Ersman, Peter
    et al.
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Eriksson, Jerry
    RISE Research Institutes of Sweden, Built Environment, Building and Real Estate. Elitfönster AB, Sweden.
    Jakonis, Darius
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Pantzare, Sandra
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Åhlin, Jessica
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Strandberg, Jan
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Sundin, Stefan
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Toss, Henrik
    RISE Research Institutes of Sweden, Digital Systems, Mobility and Systems.
    Ahrentorp, Fredrik
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Daoud, Kaies
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Jonasson, Christian
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Svensson, Henrik
    Elitfönster AB, Sweden.
    Gregard, Greger
    ChromoGenics AB, Sweden.
    Näslund, Ulf
    Vasakronan AB, Sweden.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Integration of Screen Printed Piezoelectric Sensors for Force Impact Sensing in Smart Multifunctional Glass Applications2022In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 24, no 11, article id 2200399Article in journal (Refereed)
    Abstract [en]

    Screen printed piezoelectric polyvinylidene fluoride?trifluoro ethylene (PVDF?TrFE)-based sensors laminated between glass panes in the temperature range 80?110?°C are presented. No degradation of the piezoelectric signals is observed for the sensors laminated at 110?°C, despite approaching the Curie temperature of the piezoelectric material. The piezoelectric sensors, here monitoring force impact in smart glass applications, are characterized by using a calibrated impact hammer system and standardized impact situations. Stand-alone piezoelectric sensors and piezoelectric sensors integrated on poly(methyl methacrylate) are also evaluated. The piezoelectric constants obtained from the measurements of the nonintegrated piezoelectric sensors are in good agreement with the literature. The piezoelectric sensor response is measured by using either physical electrical contacts between the piezoelectric sensors and the readout electronics, or wirelessly via both noncontact capacitive coupling and Bluetooth low-energy radio link. The developed sensor concept is finally demonstrated in smart window prototypes, in which integrated piezoelectric sensors are used to detect break-in attempts. Additionally, each prototype includes an electrochromic film to control the light transmittance of the window, a screen printed electrochromic display for status indications and wireless communication with an external server, and a holistic approach of hybrid printed electronic systems targeting smart multifunctional glass applications.

  • 6.
    Baresel, Christian
    et al.
    IVL Swedish Environmental Research Institute AB, Sweden.
    Schaller, Vincent
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Jonasson, Christian
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Johansson, Christer
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Bordes, Romain
    Chalmers University of Technology, Sweden.
    Chauhan, Vinay
    Chalmers University of Technology, Sweden.
    Sugunan, Abhilash
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Sommertune, Jens
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Welling, Sebastian
    IVL Swedish Environmental Research Institute AB, Sweden.
    Functionalized magnetic particles for water treatment2019In: Heliyon, E-ISSN 2405-8440, Vol. 5, no 8, article id e02325Article in journal (Refereed)
    Abstract [en]

    In this study, we have taken the concept of water treatment by functionalized magnetic particles one step forward by integrating the technology into a complete proof of concept, which included the preparation of surface modified beads, their use as highly selective absorbents for heavy metals ions (Zinc, Nickel), and their performance in terms of magnetic separation. The separation characteristics were studied both through experiments and by simulations. The data gathered from these experimental works enabled the elaboration of various scenarios for Life Cycle Analysis (LCA). The LCA showed that the environmental impact of the system is highly dependent on the recovery rate of the magnetic particles. The absolute impact on climate change varied significantly among the scenarios studied and the recovery rates. The results support the hypothesis that chelation specificity, magnetic separation and bead recovery should be optimized to specific targets and applications. 

  • 7.
    Bender, P.
    et al.
    University of Cantabria, Spain .
    Bogart, L. K.
    University College London, UK .
    Posth, O.
    Physikalisch-Technische Bundesanstalt, Germany .
    Szczerba, W.
    BAM Bundesanstalt für Materialforschung Und-prüfung, Germany ; AGH University of Science and Technology, Poland .
    Rogers, S. E.
    ISIS-STFC Neutron Scattering Facility, UK.
    Castro, A.
    SOLVE Research and Consultancy AB, Sweden .
    Nilsson, L.
    SOLVE Research and Consultancy AB, Sweden; Lund University, Sweden.
    Zeng, L. J.
    Chalmers University of Technology, Sweden.
    Sugunan, Abhilash
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    Sommertune, Jens
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    Fornara, A.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    González-Alonso, D.
    University of Cantabria, Spain .
    Fernández Barquín, L.
    University of Cantabria, Spain.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Structural and magnetic properties of multi-core nanoparticles analysed using a generalised numerical inversion method2017In: Scientific Reports, E-ISSN 2045-2322, Vol. 7, article id 45990Article in journal (Refereed)
    Abstract [en]

    The structural and magnetic properties of magnetic multi-core particles were determined by numerical inversion of small angle scattering and isothermal magnetisation data. The investigated particles consist of iron oxide nanoparticle cores (9 nm) embedded in poly(styrene) spheres (160 nm). A thorough physical characterisation of the particles included transmission electron microscopy, X-ray diffraction and asymmetrical flow field-flow fractionation. Their structure was ultimately disclosed by an indirect Fourier transform of static light scattering, small angle X-ray scattering and small angle neutron scattering data of the colloidal dispersion. The extracted pair distance distribution functions clearly indicated that the cores were mostly accumulated in the outer surface layers of the poly(styrene) spheres. To investigate the magnetic properties, the isothermal magnetisation curves of the multi-core particles (immobilised and dispersed in water) were analysed. The study stands out by applying the same numerical approach to extract the apparent moment distributions of the particles as for the indirect Fourier transform. It could be shown that the main peak of the apparent moment distributions correlated to the expected intrinsic moment distribution of the cores. Additional peaks were observed which signaled deviations of the isothermal magnetisation behavior from the non-interacting case, indicating weak dipolar interactions.

  • 8.
    Bender, P.
    et al.
    University of Cantabria, Spain.
    Fock, J.
    DTU Technical University of Denmark, Denmark.
    Hansen, M. F.
    DTU Technical University of Denmark, Denmark.
    Bogart, L. K.
    UCL University College London, UK.
    Southern, P.
    UCL University College London, UK.
    Ludwig, F.
    Technische Universität Braunschweig, Germany.
    Wiekhorst, F.
    PTB Physikalisch-Technische Bundesanstalt, Germany.
    Szczerba, W.
    Bundesanstalt für Materialforschung und -prüfung, Germany; AGH University of Science and Technology, Poland.
    Zeng, L. J.
    Chalmers University of Technology, Sweden.
    Heinke, D.
    nanoPET Pharma GmbH, Germany.
    Gehrke, N.
    nanoPET Pharma GmbH, Germany.
    Díaz, M. T. F.
    Institut Laue Langevin, France.
    González-Alonso, D.
    University of Cantabria, Spain.
    Espeso, J. I.
    University of Cantabria, Spain.
    Fernández, J. R.
    University of Cantabria, Spain.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Influence of clustering on the magnetic properties and hyperthermia performance of iron oxide nanoparticles2018In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 29, no 42, article id 425705Article in journal (Refereed)
    Abstract [en]

    Clustering of magnetic nanoparticles can drastically change their collective magnetic properties, which in turn may influence their performance in technological or biomedical applications. Here, we investigate a commercial colloidal dispersion (FeraSpin™R), which contains dense clusters of iron oxide cores (mean size around 9 nm according to neutron diffraction) with varying cluster size (about 18-56 nm according to small angle x-ray diffraction), and its individual size fractions (FeraSpin™XS, S, M, L, XL, XXL). The magnetic properties of the colloids were characterized by isothermal magnetization, as well as frequency-dependent optomagnetic and AC susceptibility measurements. From these measurements we derive the underlying moment and relaxation frequency distributions, respectively. Analysis of the distributions shows that the clustering of the initially superparamagnetic cores leads to remanent magnetic moments within the large clusters. At frequencies below 105 rad s-1, the relaxation of the clusters is dominated by Brownian (rotation) relaxation. At higher frequencies, where Brownian relaxation is inhibited due to viscous friction, the clusters still show an appreciable magnetic relaxation due to internal moment relaxation within the clusters. As a result of the internal moment relaxation, the colloids with the large clusters (FS-L, XL, XXL) excel in magnetic hyperthermia experiments.

  • 9.
    Bender, P.
    et al.
    University of Cantabria, Spain.
    Wetterskog, E.
    Uppsala University, Sweden.
    Honecker, D.
    Institut Laue-Langevin, France.
    Fock, J.
    DTU Technical University of Denmark, Denmark.
    Frandsen, C.
    DTU Technical University of Denmark, Denmark.
    Moerland, C.
    Technische Universiteit Eindhoven, The Netherlands.
    Bogart, L. K.
    University College London, UK.
    Posth, O.
    Physikalisch-Technische Bundesanstalt, Germany.
    Szczerba, W.
    Bundesanstalt für Materialforschung und-prüfung, Germany; AGH University of Science and Technology, Poland.
    Gavilán, H.
    Instituto de Ciencia de Materiales de Madrid, Spain.
    Costo, R.
    CSIC Instituto de Ciencia de Materiales de Madrid, Spain.
    Fernández-Díaz, M. T.
    Institut Laue-Langevin, France.
    González-Alonso, D.
    University of Cantabria, Spain.
    Fernández Barquín, L.
    University of Cantabria, Spain.
    Johansson, Christer
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Dipolar-coupled moment correlations in clusters of magnetic nanoparticles2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 22, article id 224420Article in journal (Refereed)
    Abstract [en]

    Here, we resolve the nature of the moment coupling between 10-nm dimercaptosuccinic acid-coated magnetic nanoparticles. The individual iron oxide cores were composed of >95% maghemite and agglomerated to clusters. At room temperature the ensemble behaved as a superparamagnet according to Mössbauer and magnetization measurements, however, with clear signs of dipolar interactions. Analysis of temperature-dependent ac susceptibility data in the superparamagnetic regime indicates a tendency for dipolar-coupled anticorrelations of the core moments within the clusters. To resolve the directional correlations between the particle moments we performed polarized small-angle neutron scattering and determined the magnetic spin-flip cross section of the powder in low magnetic field at 300 K. We extract the underlying magnetic correlation function of the magnetization vector field by an indirect Fourier transform of the cross section. The correlation function suggests nonstochastic preferential alignment between neighboring moments despite thermal fluctuations, with anticorrelations clearly dominating for next-nearest moments. These tendencies are confirmed by Monte Carlo simulations of such core clusters.

  • 10.
    Bjurström, Johan
    et al.
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware. Chalmers University of Technology, Sweden.
    Ohlsson, Fredrik
    RISE Research Institutes of Sweden. Umeå University, Sweden.
    Rusu, Cristina
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware. Chalmers University of Technology, Sweden.
    Unified Modeling and Analysis of Vibration Energy Harvesters under Inertial Loads and Prescribed Displacements2022In: Applied Sciences: APPS, E-ISSN 1454-5101, Vol. 12, no 19Article in journal (Refereed)
    Abstract [en]

    In this paper, we extend the optimization analysis found in the current literature for single-degree-of-freedom vibrational energy harvesters. We numerically derive and analyze the optimization conditions based on unified expressions for piezoelectric and electromagnetic energy harvesters. Our contribution lies in the detailed analysis and comparison of both resonant and anti-resonant states while fully including the effect of intrinsic resistance. We include both the case of excitation by inertial load and prescribed displacement, as the latter has not been elaborated on in the previous literature and provides new insights. We perform a general analysis but also consider typical values of applied piezoelectric and electromagnetic energy harvesters. Our results improve upon previous similar comparative studies by providing new and useful insights regarding optimal load, load power and power input to output efficiency. Our analysis shows an exponential increase in the critical mechanical quality factor due to the resistive loss coefficient. We find that the ratio of mechanical quality factor to resistive loss coefficient, at resonance, increases drastically close to the theoretical maximum for load power. Under the same optimization conditions, an equivalent conclusion can be drawn regarding efficiency. We find that the efficiency at anti-resonance behaves differently and is equal to or larger than the efficiency at resonance. We also show that the optimal load coefficient at resonance has a significant dependence on the mechanical quality factor only when the resistive loss coefficient is large. Our comparison of excitation types supports the previous literature, in a simple and intuitive way, regarding optimal load by impedance matching and power output efficiency. Our modeling and exploration of new parameter spaces provide an improved tool to aid the development of new harvester prototypes.

  • 11.
    Bjurström, Johan
    et al.
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware. Chalmers University of Technology, Sweden .
    Ohlsson, Fredrik
    RISE Research Institutes of Sweden. Umeå University, Sweden.
    Vikerfors, Andreas
    ReVibe Energy AB, Sweden.
    Rusu, Cristina
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Tunable spring balanced magnetic energy harvester for low frequencies and small displacements2022In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 259, article id 115568Article in journal (Refereed)
    Abstract [en]

    In this paper we present a novel concept to efficiently harvest vibrational energy at low frequencies and very small displacement. We describe and evaluate an electromagnetic energy harvester which generates power from a magnetic circuit with motion induced variations of an air gap. External vibrations induce oscillations of the gap length around an equilibrium point, due to a linear spring counteracting the magnetic force. The relative position of the spring can be adjusted to optimize the harvester output for excitation amplitude and frequency. A simulation model is built in COMSOL and verified by comparison with lab measurements. The simulation model is used to determine the potential performance of the proposed concept under both harmonic and non-harmonic excitation. Under harmonic excitation, we achieve a simulated RMS load power of 26.5 μW at 22 Hz and 0.028 g acceleration amplitude. From a set of comparable EH we achieve the highest theoretical power metric of 1712.2 µW/cm3/g2 while maintaining the largest relative bandwidth of 81.8%. Using measured non-harmonic vibration data, with a mean acceleration of 0.039 g, resulted in a mean power of 52 μW. Moreover, the simplicity and robustness of our design makes it a competitive alternative for use in practical situations. © 2022 The Author(s)

  • 12.
    Blomgren, Jakob
    et al.
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Ahrentorp, Fredrik
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Ilver, Dag
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Jonasson, Christian
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Sepehri, Sobhan
    Chalmers University of Technology, Sweden.
    Kalaboukhov, Alexei
    Chalmers University of Technology, Sweden.
    Winkler, Dag
    Chalmers University of Technology, Sweden.
    de la Torre, Tereza
    Uppsala University, Sweden.
    Strømme, Maria
    Uppsala University, Sweden.
    Johansson, Christer
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Development of a sensitive induction-based magnetic nanoparticle biodetection method2018In: Nanomaterials, E-ISSN 2079-4991, Vol. 8, no 11, article id 887Article in journal (Refereed)
    Abstract [en]

    We developed a novel biodetection method for influenza virus based on AC magnetic susceptibility measurement techniques (the DynoMag induction technique) together with functionalized multi-core magnetic nanoparticles. The sample consisting of an incubated mixture of magnetic nanoparticles and rolling circle amplified DNA coils is injected into a tube by a peristaltic pump. The sample is moved as a plug to the two well-balanced detection coils and the dynamic magnetic moment in each position is read over a range of excitation frequencies. The time for making a complete frequency sweep over the relaxation peak is about 5 minutes (10 Hz–10 kHz with 20 data points). The obtained standard deviation of the magnetic signal at the relaxation frequency (around 100 Hz) is equal to about 10−5 (volume susceptibility SI units), which is in the same range obtained with the DynoMag system. The limit of detection with this method is found to be in the range of 1 pM.

  • 13.
    Bogren, Sara
    et al.
    RISE, Swedish ICT, Acreo.
    Fornara, Andrea
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Ludwig, Frank
    Technical University of Braunschweig, Germany.
    Del Puerto Morales, Maria
    Instituto de Ciencia de Materiales de Madrid, Spain.
    Steinhoff, Uwe
    PTB Physikalisch-Technische Bundesanstalt, Germany.
    Fougt Hansen, Mikkel
    DTU Technical University of Denmark, Denmark.
    Kazakova, Olga
    NPL National Physical Laboratory, UK.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Classification of Magnetic Nanoparticle Systems—Synthesis, Standardization and Analysis Methods in the NanoMag Project2015In: International Journal of Molecular Sciences, ISSN 1661-6596, E-ISSN 1422-0067, Vol. 16, no 9, p. 20308-20325Article in journal (Refereed)
    Abstract [en]

    This study presents classification of different magnetic single- and multi-core particle systems using their measured dynamic magnetic properties together with their nanocrystal and particle sizes. The dynamic magnetic properties are measured with AC (dynamical) susceptometry and magnetorelaxometry and the size parameters are determined from electron microscopy and dynamic light scattering. Using these methods, we also show that the nanocrystal size and particle morphology determines the dynamic magnetic properties for both single- and multi-core particles. The presented results are obtained from the four year EU NMP FP7 project, NanoMag, which is focused on standardization of analysis methods for magnetic nanoparticles.

  • 14.
    Burger, Paul
    et al.
    Chalmers University of Technology, Sweden; Johannes Gutenberg University Mainz, Germany.
    Singh, G.
    Chalmers University of Technology, Sweden; Institute of Materials Science of Barcelona , Spain.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware. Chalmers University of Technology, Sweden.
    Moya, Carlos
    Université Libre de Bruxelles, Belgium.
    Bruylants, Gilles
    Université Libre de Bruxelles, Belgium.
    Jakob, Gerhard
    Johannes Gutenberg University Mainz, Germany.
    Kalaboukhov, Alexei
    Chalmers University of Technology, Sweden.
    Atomic Force Manipulation of Single Magnetic Nanoparticles for Spin-Based Electronics2022In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 16, no 11, p. 19253-19260Article in journal (Refereed)
    Abstract [en]

    Magnetic nanoparticles (MNPs) are instrumental for fabrication of tailored nanomagnetic structures, especially where top-down lithographic patterning is not feasible. Here, we demonstrate precise and controllable manipulation of individual magnetite MNPs using the tip of an atomic force microscope. We verify our approach by placing a single MNP with a diameter of 50 nm on top of a 100 nm Hall bar fabricated in a quasi-two-dimensional electron gas (q2DEG) at the oxide interface between LaAlO3 and SrTiO3 (LAO/STO). A hysteresis loop due to the magnetic hysteresis properties of the magnetite MNPs was observed in the Hall resistance. Further, the effective coercivity of the Hall resistance hysteresis loop could be changed upon field cooling at different angles of the cooling field with respect to the measuring field. The effect is associated with the alignment of the MNP magnetic moment along the easy axis closest to the external field direction across the Verwey transition in magnetite. Our results can facilitate experimental realization of magnetic proximity devices using single MNPs and two-dimensional materials for spin-based nanoelectronics. © 2022 The Authors. 

  • 15.
    Carlsson, Raul
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, SWECAST.
    Elmquist, Lennart
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, SWECAST.
    Thore, Andreas
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, SWECAST.
    Ahrentorp, Fredrik
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Johansson, Christer
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Israelsson, Björn
    SKF Mekan AB, Sweden.
    Connecting sensors inside smart castings2018Conference paper (Refereed)
    Abstract [en]

    The paper presents ongoing research on smart metal castings, meaning the technologicalinnovation of elevating cast metal components into metal components with integratedsensor functionality. Since the innovation targets aim straight at low cost industrial serialproduction, specific high cost and high-end solutions like inclusion of advancedelectronic equipment and after mounted sensors are not part of this innovationdevelopment. Integrating signal carriers inside metal castings to achieve metal castingswith sensor functionality requires robust solutions for connecting the sensor signal to thesensor interrogator and interpreter. The actual transmission of the signal may be donewirelessly or by wire. However, for several reasons there is a challenge with establishingan isolated and distinct connection between the sensor contact, and the contact at theexternal connection, regardless of whether it is to an antenna for wireless transmission orto a wire. This paper presents metallurgical challenges associated with choices ofmaterials, and combinations of metallurgical challenges and production process relatedchallenges, including the high melting temperatures. Aims are to find the rightcombinations of metal alloys, production simplicity, signal stability and robustness. Thepaper will present some of the tests made in the project so far. The project is run in aconsortium of the two Sweden-based industrial companies Husqvarna and SKF, and thetwo Swedish research institutes Swerea SWECAST and RISE Acreo.

  • 16.
    Chakkarapani, Prabu
    et al.
    Anna University, India.
    Subbiah, Latha
    Anna University, India.
    Palanisamy, Selvamani
    Anna University, India.
    Bibiana, Arputha
    Anna University, India.
    Ahrentorp, Fredrik
    RISE, Swedish ICT, Acreo.
    Jonasson, Christian
    RISE, Swedish ICT, Acreo.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Encapsulation of methotrexate loaded magnetic microcapsules for magnetic drug targeting and controlled drug release2015In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 380, p. 285-294Article in journal (Refereed)
    Abstract [en]

    We report on the development and evaluation of methotrexate magnetic microcapsules (MMC) for targeted rheumatoid arthritis therapy. Methotrexate was loaded into CaCO3-PSS (poly (sodium 4-styrenesulfonate)) doped microparticles that were coated successively with poly (allylamine hydrochloride) and poly (sodium 4-styrenesulfonate) by layer-by-layer technique. Ferrofluid was incorporated between the polyelectrolyte layers. CaCO3-PSS core was etched by incubation with EDTA yielding spherical MMC. The MMC were evaluated for various physicochemical, pharmaceutical parameters and magnetic properties. Surface morphology, crystallinity, particle size, zeta potential, encapsulation efficiency, loading capacity, drug release pattern, release kinetics and AC susceptibility studies revealed spherical particles of ~3 µm size were obtained with a net zeta potential of +24.5 mV, 56% encapsulation and 18.6% drug loading capacity, 96% of cumulative drug release obeyed Hixson-Crowell model release kinetics. Drug excipient interaction, surface area, thermal and storage stability studies for the prepared MMC was also evaluated. The developed MMC offer a promising mode of targeted and sustained release drug delivery for rheumatoid arthritis therapy.

  • 17.
    Chen, Hao
    et al.
    Carnegie Mellon University, USA.
    Billington, David
    Cardiff University, UK.
    Riordan, Edward
    Cardiff University, UK.
    Blomgren, Jakob
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Giblin, Sean
    Cardiff University, UK.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Majetich, Sara
    Carnegie Mellon University, USA.
    Tuning the dynamics in Fe3O4nanoparticles for hyperthermia optimization2020In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 117, no 7, article id 073702Article in journal (Refereed)
    Abstract [en]

    The AC magnetic susceptibility (ACS) of Fe3O4 nanoparticles was measured between 10 kHz and 4 MHz at different temperatures and in applied DC fields. In this frequency range, magnetostatic interactions impact magnetization dynamics even for dilute assemblies. The ACS spectrum of relaxation frequencies changes both with temperature and the addition of a small DC field. Because both the relaxation peak frequency and amplitude can be tuned with the DC field, these results could be applied to magnetic hyperthermia applications to optimize heat delivery. 

  • 18.
    Elmquist, Lennart
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, SWECAST.
    Carlsson, Raul
    RISE - Research Institutes of Sweden, Materials and Production, SWECAST.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Cast iron components with intelligence2018Conference paper (Refereed)
    Abstract [en]

    The paper describes a project with the aim to develop communicating and functional cast iron components in smart systems. The concept is based on sensors integrated into cast iron components; this will influence not only the component but also the casting process. Among the technical challenges is how to choose a sensor solution that cost-efficiently and with minimal environmental impact can be integrated into the component during the casting process, and especially without being damaged during mold filling and the high pouring temperature. Another challenge is how the iron will interact and interfere with sensor signals and whether an insulating intermediate material is needed or not. Integrating the sensors into the casting makes sensors a natural part of the component, which in turn can lead to more resource efficient designs, increased value added for the casting sector, and a general access to different possibilities of digitalization. The integrated sensors can be used for effective control and monitoring of components when in service and give information about for example how the component is used and what conditions it is exposed to. In other words, the component can tell when maintenance is needed or in worst cases, indicate that something is wrong before a failure will happen. Important measurands can e.g. be elongation, shear, temperature and vibration. Different combinations of sensor materials and insulating materials and their interaction with the cast iron have been investigated. It is shown how the interaction at the interface affects the microstructure and consequently the properties of the cast iron. In the case of insulating materials it is e.g. shown how air gaps are formed and in the case of sensor materials it is shown how a diffusion zone is formed and how this zone depends on the sensor material. How this diffusion zone affects the microstructure is discussed.

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  • 19.
    Ferguson, Richard Matthew
    et al.
    University of Washington, USA.
    Khandhar, Amit P.
    University of Washington, USA.
    Johansson, Christian
    RISE, Swedish ICT, Acreo.
    Blomgren, Jakob
    RISE, Swedish ICT, Acreo.
    Johansson, Christer
    Krishnan, K. M.
    University of Washington, USA.
    Size-Dependent Relaxation Properties of Monodisperse Magnetite Nanoparticles Measured Over Seven Decades of Frequency by AC Susceptometry2013In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 49, p. 3441-3444Article in journal (Refereed)
    Abstract [en]

    Magnetic relaxation is exploited in innovative biomedical applications of magnetic particles such as magnetic particle imaging (MPI), magnetic fluid hyperthermia, and bio-sensing. Relaxation behavior should be optimized to achieve high performance imaging, efficient heating, and good SNR in bio-sensing. Using two AC susceptometers with overlapping frequency ranges, we have measured the relaxation behavior of a series of monodisperse magnetic particles and demonstrated that this approach is an effective way to probe particle relaxation characteristics from a few Hz to 10 MHz, the frequencies relevant for MPI, hyperthermia, and sensing.

  • 20.
    Fock, Jeppe
    et al.
    DTU Technical University of Denmark, Denmark .
    Jonasson, Christian
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Hansen, Mikkel F.
    DTU Technical University of Denmark, Denmark .
    Characterization of fine particles using optomagnetic measurements2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 13, p. 8802-8814Article in journal (Refereed)
    Abstract [en]

    The remanent magnetic moment and the hydrodynamic size are important parameters for the synthesis and applications of magnetic nanoparticles (MNPs). We present the theoretical basis for the determination of the remanent magnetic moment and the hydrodynamic size of MNPs with a narrow size distribution using optomagnetic measurements. In these, the 2nd harmonic variation of the intensity of light transmitted through an MNP suspension is measured as a function of an applied axial oscillating magnetic field. We first show how the measurements of the optomagnetic signal magnitude at a low frequency vs. magnetic field amplitude can be used to determine the MNP moment. Subsequently, we use linear response theory to describe the dynamic non-equilibrium response of the MNP suspension at low magnetic field amplitudes and derive a link between optomagnetic measurements and magnetic AC susceptibility measurements. We demonstrate the presented methodology on two samples of commercially available multi-core MNPs. The results compare well with those obtained by dynamic light scattering, AC susceptibility and vibrating sample magnetometry measurements on the same samples when the different weighting of the particle size in the techniques is taken into account. The optomagnetic technique is simple, fast and does not require prior knowledge of the concentration of MNPs and it thus has the potential to be used as a routine tool for quality control of MNPs.

  • 21.
    Fonnum, Geir
    et al.
    Dynal Biotech ASA, Norway.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Molteberg, Astrid
    Dynal Biotech ASA, Norway.
    Aksnes, Elin
    Dynal Biotech ASA, Norway.
    Mörup, Steen
    DTU Technical University of Denmark, Denmark.
    Characterization of Dynabeads® by magnetization measurements Mössbauer spectroscopy2005In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 293, p. 41-47Article in journal (Refereed)
    Abstract [en]

    X-ray diffraction, SEM analysis, Mössbauer spectroscopy and magnetic measurements were used to characterize three different magnetic beads (Dynabeads®). Maghemite (γ-Fe2O3) is the predominant crystalline phase. The nanoparticles were evenly spread in the beads, and the crystal sizes were in the range of 8 nm. The nanoparticles showed superparamagnetic behaviour. The particle's intrinsic magnetization of about 340 kA/m is typical for nanoparticles of maghemite.

  • 22.
    Fornara, Andrea
    et al.
    KTH Royal Institute of Technology, Sweden.
    Johansson, Petter
    RISE, Swedish ICT, Acreo.
    Petersson, Karolina
    RISE - Research Institutes of Sweden (2017-2019), ICT, Acreo.
    Gustafsson, Stefan
    Chalmers University of Technology, Sweden.
    Qin, Jian
    KTH Royal Institute of Technology, Sweden.
    Olsson, Eva
    Chalmers University of Technology, Sweden.
    Ilver, Dag
    RISE, Swedish ICT, Acreo.
    Krozer, Anatol
    RISE, Swedish ICT, Acreo.
    Muhammed, Mamoun A.
    KTH Royal Institute of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Tailored Magnetic Nanoparticles for Direct Sensitive Detection of Biomolecules in Biological Samples2008In: Nano Letters, Vol. 8, no 10, p. 3423-28Article in journal (Refereed)
    Abstract [en]

    We developed nanoparticles with tailored magnetic properties for direct and sensitive detection of biomolecules in biological samples in a single step. Thermally blocked nanoparticles obtained by thermal hydrolysis, functionalized with specific ligands, are mixed with sample solutions, and the variation of the magnetic relaxation due to surface binding is used to detect the presence of biomolecules. The binding significantly increases the hydrodynamic volume of nanoparticles, thus changing their Brownian relaxation frequency which is measured by a specifically developed AC susceptometer. The system was tested for the presence of Brucella antibodies, a dangerous pathogen causing brucellosis with severe effects both on humans and animals, in serum samples from infected cows and the surface of the nanoparticles was functionalized with lipopolysaccarides (LPS) from Brucella abortus. The hydrodynamic volume of LPS-functionalized particles increased by 25-35% as a result of the binding of the antibodies, measured by changes in the susceptibility in an alternating magnetic field. The method has shown high sensitivity, with detection limit of 0.05 μgmL-1 of antibody in the biological samples without any pretreatment. This magnetic- based assay is very sensitive, cost-efficient, and versatile, giving a direct indication whether the animal is infected or not, making it suitable for point-of-care applications. The functionalization of tailored magnetic nanoparticles can be modified to suit numerous homogeneous assays for a wide range of applications.

  • 23.
    Fortes Brollo, Maria Eugenia
    et al.
    Instituto de Ciencia de Materiales de Madrid, Spain.
    Domínguez-Bajo, Ana
    Instituto de Ciencia de Materiales de Madrid, Spain.
    Tabero, Andrea
    Universidad Autónoma de Madrid, Spain.
    Domínguez-Arca, Vicente
    Universidad de Santiago de Compostela, Spain.
    Gisbert, Victor
    Instituto de Ciencia de Materiales de Madrid, Spain.
    Prieto, Gerardo
    Universidad de Santiago de Compostela, Spain.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Garcia, Ricardo
    Instituto de Ciencia de Materiales de Madrid, Spain.
    Villanueva, Angeles
    Universidad Autónoma de Madrid, Spain.
    Serrano, María Concepción
    Instituto de Ciencia de Materiales de Madrid, Spain.
    Morales, María Del Puerto
    Instituto de Ciencia de Materiales de Madrid, Spain; IMDEA-Nanociencia, Spain.
    Combined Magnetoliposome Formation and Drug Loading in One Step for Efficient Alternating Current-Magnetic Field Remote-Controlled Drug Release.2020In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 12, no 4, p. 4295-4307Article in journal (Refereed)
    Abstract [en]

    We have developed a reproducible and facile one step strategy for the synthesis of doxorubicin loaded magnetoliposomes by using a thin-layer evaporation method. Liposomes of around 200 nm were made of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and iron oxide nanoparticles (NPs) with negative, positive, and hydrophobic surfaces that were incorporated outside, inside, or between the lipid bilayers, respectively. To characterize how NPs are incorporated in liposomes, advanced cryoTEM and atomic force microscope (AFM) techniques have been used. It was observed that only when the NPs are attached outside the liposomes, the membrane integrity is preserved (lipid melt transition shifts to 38.7 °C with high enthalpy 34.8 J/g) avoiding the leakage of the encapsulated drug while having good colloidal properties and the best heating efficiency under an alternating magnetic field (AMF). These magnetoliposomes were tested with two cancer cell lines, MDA-MB-231 and HeLa cells. First, 100% of cellular uptake was achieved with a high cell survival (above 80%), which is preserved (83%) for doxorubicin-loaded magnetoliposomes. Then, we demonstrate that doxorubicin release can be triggered by remote control, using a noninvasive external AMF for 1 h, leading to a cell survival reduction of 20%. Magnetic field conditions of 202 kHz and 30 mT seem to be enough to produce an effective heating to avoid drug degradation. In conclusion, these drug-loaded magnetoliposomes prepared in one step could be used for drug release on demand at a specific time and place, efficiently using an external AMF to reduce or even eliminate side effects.

  • 24.
    Fortes Brollo, Maria Eugenia
    et al.
    CSIC Institute of Material Science of Madrid, Spain.
    Hernández Flores, Patricia
    CSIC Centro Nacional de Biotecnología, Spain.
    Gutiérrez, Lucía
    INA Instituto Universitario de Nanociencia de Aragón, Spain.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Barber, Domingo Francisco
    CSIC Centro Nacional de Biotecnología, Spain.
    Morales, María Del Puerto
    CSIC Institute of Material Science of Madrid, Spain.
    Magnetic properties of nanoparticles as a function of their spatial distribution on liposomes and cells2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 26, p. 17829-17838Article in journal (Refereed)
    Abstract [en]

    The aggregation processes of magnetic nanoparticles in biosystems are analysed by comparing the magnetic properties of three systems with different spatial distributions of the nanoparticles. The first one is iron oxide nanoparticles (NPs) of 14 nm synthesized by coprecipitation with two coatings, (3-aminopropyl)trimethoxysilane (APS) and dimercaptosuccinic acid (DMSA). The second one is liposomes with encapsulated nanoparticles, which have different configurations depending on the NP coating (NPs attached to the liposome surface or encapsulated in its aqueous volume). The last system consists of two cell lines (Pan02 and Jurkat) incubated with the NPs. Dynamic magnetic behaviour (AC) was analysed in liquid samples, maintaining their colloidal properties, while quasi-static (DC) magnetic measurements were performed on lyophilised samples. AC measurements provide a direct method for determining the effect of the environment on the magnetization relaxation of nanoparticles. Thus, the imaginary (χ'') component shifts to lower frequencies as the aggregation state increases from free nanoparticles to those attached or embedded into liposomes in cell culture media and more pronounced when internalized by the cells. DC magnetization curves show no degradation of the NPs after interaction with biosystems in the analysed timescale. However, the blocking temperature is shifted to higher temperatures for the nanoparticles in contact with the cells, regardless of the location, the incubation time, the cell line and the nanoparticle coating, supporting AC susceptibility data. These results indicate that the simple fact of being in contact with the cells makes the nanoparticles aggregate in a non-controlled way, which is not the same kind of aggregation caused by the contact with the cell medium nor inside liposomes.

  • 25.
    Fossheim, Sigrid L.
    et al.
    University of Oslo, Norway.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Fahlvik, Anne Kjersti
    Nycomed Imaging AS, Norway.
    Grace, David
    University of Oslo, Norway.
    Klaveness, Jo
    University of Oslo, Norway.
    Lanthanide-based susceptibility contrast agents : Assessment of the magnetic properties1996In: Magn. Reson. Med., Vol. 35, p. 201-206Article in journal (Refereed)
    Abstract [en]

    The T2* contrast efficacy of paramagnetic contrast agents is dependent on their magnetic properties. Vibrating sample magnetometry (VSM) and the Live Chan NMR method have been used to evaluate the influence of ligand structure on the bulk magnetic susceptibility (BMS) of low-molecular weight (LMW) lanthanide chelates. VSM was also used for the BMS assessment of LMW lanthanide chelates covalently attached to cross-linked starch particles. The ligand structure had no influence on the BMS of the gadolinium (Gd) and dysprosium (Dy) chelates. The mean BMS value of the Dy-chelates was 1.8 fold higher than that of the Gd-chelates. The holmium (Ho) DTPA-BMA chelate had a similar BMS to that of Oy-DTPA-BMA while the lowest BMS was found for europium (Eu(III)) DTPA-BMA. The covalent attachment of Gd-DTPA and Dy-DTPA to a cross-linked starch particle had no impact on their intrinsic magnetic properties. The BMS data were in good accordance with those obtained for non- particulate bound LMW Dy- and Gd-chelates. The magnetic susceptibility of the Gd-DTPA labeled particles was described by the Curie law, indicative of no magnetic interactions between Gd-DTPA molecules. The magnetic susceptibility of the Dy-DTPA labeled particles followed the Curie-Weiss law with a Curie- Weiss temperature of about -2 K, indicating magnetic interactions. The magnetic susceptibility of Dy-DTPA will, however, not be affected by such magnetic interactions at physiological temperatures.

  • 26.
    Gao, Shang
    et al.
    Paul Scherrer Institut, Switzerland; University of Geneva, Switzerland.
    Zaharko, Oksana
    Paul Scherrer Institut, Switzerland.
    Tsurkan, Vladimir
    University of Augsburg, Germany; Academy of Sciences of Moldova, Moldova.
    Prodan, Lilian
    Academy of Sciences of Moldova, Moldova.
    Riordan, Edvard
    Cardiff University, UK.
    Lago, Jorge
    University of the Basque Country, Spain.
    Fak, Björn
    Institut Laue-Langevin, France.
    Wildes, Andrew R.
    Institut Laue-Langevin, France.
    Koza, Marek M.
    Institut Laue-Langevin, France.
    Ritter, Clemens
    Institut Laue-Langevin, France.
    Fouquet, Peter
    Institut Laue-Langevin, France.
    Keller, Lukas
    Paul Scherrer Institut, Switzerland.
    Canevet, Emmanuel
    Paul Scherrer Institut, Switzerland; DTU Technical University of Denmark, Denmark.
    Medarde, Marisa
    Paul Scherrer Institut, Switzerland.
    Blomgren, Jakob
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Giblin, Sean R.
    Cardiff University, UK.
    Vrtnik, Stanislav
    Jozef Stefan Institute, Slovenia.
    Luzar, Jose
    Jozef Stefan Institute, Slovenia.
    Loidl, Alois
    University of Augsburg, Germany.
    Ruegg, Christina
    Paul Scherrer Institut, Switzerland; University of Geneva, Switzerland.
    Fennell, Tom
    Paul Scherrer Institut, Switzerland.
    Dipolar Spin Ice States with a Fast Monopole Hopping Rate in CdEr2X4 (X = Se, S)2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 13, article id 130201Article in journal (Refereed)
    Abstract [en]

    Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr2Se4 is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy2Ti2O7. In this Letter we use diffuse neutron scattering to show that both CdEr2Se4 and CdEr2S4 support a dipolar spin ice state-the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy2Ti2O7, i.e., dilute and uncorrelated, and so cannot provide three orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er3+ ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr2X4 (X = Se, S) are primarily due to much faster monopole hopping. Our work suggests that CdEr2X4 offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples.

  • 27.
    Gavilán, Helena
    et al.
    CSIC Instituto de Ciencia de Materiales de Madrid, Spain.
    Kowalski, Anja
    Micromod Partikeltechnologie GmbH, Germany.
    Heinke, David
    NanoPET Pharma GmbH, Germany.
    Sugunan, Abhilash
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    Sommertune, Jens
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    Varón, Miriam
    DTU Technical University of Denmark, Denmark.
    Bogart, Lara K.
    UCL University College London, UK.
    Posth, Oliver
    PTB Physikalisch-Technische Bundesanstalt, Germany.
    Zeng, Lunjie
    Chalmers University of Technology, Sweden.
    González-Alonso, David
    University of Cantabria, Spain.
    Balceris, Chrsitoph
    TU Braunschweig, Germany.
    Fock, Jeppe
    DTU Technical University of Denmark, Denmark.
    Wetterskog, Erik
    Uppsala University, Sweden.
    Frandsen, Cathrine
    DTU Technical University of Denmark, Denmark.
    Gehrke, Nicole
    NanoPET Pharma GmbH, Germany.
    Grüttner, Cordula
    Micromod Partikeltechnologie GmbH, Germany.
    Fornara, Andrea
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    Ludwig, Frank
    TU Braunschweig, Germany.
    Veintemillas-Verdaguer, Sabino
    CSIC Instituto de Ciencia de Materiales de Madrid, Spain.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Morales, M. Puerto
    CSIC Instituto de Ciencia de Materiales de Madrid, Spain.
    Colloidal Flower-Shaped Iron Oxide Nanoparticles: Synthesis Strategies and Coatings2017In: Particle & particle systems characterization, ISSN 0934-0866, E-ISSN 1521-4117, Vol. 34, no 7, article id 1700094Article in journal (Refereed)
    Abstract [en]

    The assembly of magnetic cores into regular structures may notably influence the properties displayed by a magnetic colloid. Here, key synthesis parameters driving the self-assembly process capable of organizing colloidal magnetic cores into highly regular and reproducible multi-core nanoparticles are determined. In addition, a self-consistent picture that explains the collective magnetic properties exhibited by these complex assemblies is achieved through structural, colloidal, and magnetic means. For this purpose, different strategies to obtain flower-shaped iron oxide assemblies in the size range 25–100 nm are examined. The routes are based on the partial oxidation of Fe(OH)2, polyol-mediated synthesis or the reduction of iron acetylacetonate. The nanoparticles are functionalized either with dextran, citric acid, or alternatively embedded in polystyrene and their long-term stability is assessed. The core size is measured, calculated, and modeled using both structural and magnetic means, while the Debye model and multi-core extended model are used to study interparticle interactions. This is the first step toward standardized protocols of synthesis and characterization of flower-shaped nanoparticles.

  • 28.
    González-Alonso, David
    et al.
    University of Cantabria, Spain.
    Espeso, Jose I.
    University of Cantabria, Spain.
    Gavilán, Helena
    ICMM/CSIC Instituto de Ciencia de Materiales de Madrid, Spain.
    Zeng, Lunjie
    Chalmers University of Technology, Sweden.
    Fernandez-Diaz, Maria Teresa
    Institut Laue-Langevin, France.
    Subías, Gloria
    Universidad de Zaragoza, Spain.
    de Pedro, Imanol
    University of Cantabria, Spain.
    Rogriguez, Jesus
    University of Cantabria, Spain.
    Bender, Philipp
    University of Cantabria, Spain.
    Fernandez Barquin, Luis
    University of Cantabria, Spain.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Identifying the presence of magnetite in an ensemble of Iron-oxide nanoparticles: A comparative Neutron diffraction study between bulk and nanoscale.2021In: Nanoscale Advances, E-ISSN 2516-0230, Vol. 3, p. 3491-Article in journal (Refereed)
    Abstract [en]

    Scientific interest in iron–oxides and in particular magnetite has been renewed due to the broad scope of its fascinating properties, which are finding applications in electronics and biomedicine. Specifically, iron oxide nanoparticles (IONPs) are gathering attraction in biomedicine. Their cores are usually constituted by a mixture of maghemite/magnetite phases. In view of this, to fine-tune the properties of an ensemble of IONPs towards their applications, it is essential to enhance mass fabrication processes towards the production of monodispersed IONPs with controlled size, shape, and stoichiometry. We exploit the vacancy sensitivity of the Verwey transition to detect the presence of magnetite. Here we are providing a direct evidence of the Verwey transition in an ensemble of IONPs through neutron diffraction. This transition is observed as a variation in the Fe moment at the octahedral sites and, in turn, gives rise to a change of the net magnetic moment. Finally, we show this variation as the microscopic ingredient driving the characteristic kink that hallmarks the Verwey transition in thermal variation of magnetization.

  • 29.
    González-Alonso, David
    et al.
    University of Cantabria, Spain.
    González, Jesús
    University of Cantabria, Spain.
    Gavilán, Helena
    Instituto de Ciencia de Materiales de Madrid, Spain.
    Fock, Jeppe
    DTU Technical University of Denmark, Denmark.
    Zeng, Lunjie
    Chalmers University of Technology, Sweden.
    Witte, Kerstin
    Institute of Physics, University of Rostock, Germany.
    Bender, Philipp
    University of Cantabria, Spain.
    Barquín, Luis Fernández
    University of Cantabria, Spain.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Revealing a masked Verwey transition in nanoparticles of coexisting Fe-oxide phases2021In: RSC Advances, Vol. 11, no 1, p. 390-396Article in journal (Refereed)
    Abstract [en]

    The attractive electronic and magnetic properties together with their biocompatibility make iron-oxide nanoparticles appear as functional materials. In Fe-oxide nanoparticle (IONP) ensembles, it is crucial to enhance their performance thanks to controlled size, shape, and stoichiometry ensembles. In light of this, we conduct a comprehensive investigation in an ensemble of ca. 28 nm cuboid-shaped IONPs in which all the analyses concur with the coexistence of magnetite/maghemite phases in their cores. Here, we are disclosing the Verwey transition by temperature dependent (4–210 K) Raman spectroscopy.

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  • 30.
    Gu, Yuanyu
    et al.
    Nanjing Tech University, China; University of Zaragoza, Spain.
    Yoshikiyo, Marie
    Namai, Asuka
    University of Tokyo, Japan.
    Bonvin, Debora
    Ecole Polytechnique Fédérale de Lausanne, Switzerland .
    Martinez, Abelarda
    Universidad de Zaragoza, Spain .
    Piñol, Rafael
    University of Zaragoza, Spain.
    Téllez, Pedro
    Universidad de Zaragoza, Spain .
    Silva, Nuno
    Universidade de Aveiro, Portugal .
    Ahrentorp, Fredrik
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Johansson, Christer
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Marco-Brualla, Joaquin
    Universidad de Zaragoza, Spain .
    Moreno-Loshuertos, Raquel
    Universidad de Zaragoza, Spain .
    Fernández-Silva, Patricio
    Universidad de Zaragoza, Spain .
    Cui, Yuwen
    Nanjing Tech University, China .
    Ohkoshi, Shin-ichi
    University of Tokyo, Japan.
    Millán, Angel
    University of Zaragoza, Spain.
    Magnetic hyperthermia with ϵ-Fe2O3nanoparticles2020In: RSC Advances, E-ISSN 2046-2069, Vol. 10, no 48, p. 28786-28797Article in journal (Refereed)
    Abstract [en]

    Biocompatibility restrictions have limited the use of magnetic nanoparticles for magnetic hyperthermia therapy to iron oxides, namely magnetite (Fe3O4) and maghemite (γ-Fe2O3). However, there is yet another magnetic iron oxide phase that has not been considered so far, in spite of its unique magnetic properties: ϵ-Fe2O3. Indeed, whereas Fe3O4 and γ-Fe2O3 have a relatively low magnetic coercivity, ϵ-Fe2O3 exhibits a giant coercivity. In this report, the heating power of ϵ-Fe2O3 nanoparticles in comparison with γ-Fe2O3 nanoparticles of similar size (∼20 nm) was measured in a wide range of field frequencies and amplitudes, in uncoated and polymer-coated samples. It was found that ϵ-Fe2O3 nanoparticles primarily heat in the low-frequency regime (20-100 kHz) in media whose viscosity is similar to that of cell cytoplasm. In contrast, γ-Fe2O3 nanoparticles heat more effectively in the high frequency range (400-900 kHz). Cell culture experiments exhibited no toxicity in a wide range of nanoparticle concentrations and a high internalization rate. In conclusion, the performance of ϵ-Fe2O3 nanoparticles is slightly inferior to that of γ-Fe2O3 nanoparticles in human magnetic hyperthermia applications. However, these ϵ-Fe2O3 nanoparticles open the way for switchable magnetic heating owing to their distinct response to frequency. 

  • 31. Gustafsson, S
    et al.
    Fornara, A
    Petersson, K
    Muhammed, M
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Olsson, E
    Evolution of structural magnetic properties of magnetite nanoparticles for biomedical applications2010In: Crystal Growth & Design, Vol. 10, no 5, p. 2278-84Article in journal (Refereed)
  • 32. Gustafsson, S
    et al.
    Fornara, A
    Ye, F
    Petersson, K
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Muhammed, M
    Olsson, E
    TEM investigation of magnetite nanoparticles for biomedical applications2008In: EMC, Vol. 2, p. 209-Article in journal (Refereed)
  • 33.
    Gutiérrez, Lucía
    et al.
    CSIC Spanish National Research Council, Spain.
    Costo, Rocio
    CSIC Spanish National Research Council, Spain.
    Grüttner, Cordula
    Micromod Partikeltechnologie GmbH, Germany.
    Westphal, Fritz
    Micromod Partikeltechnologie GmbH, Germany.
    Gehrke, Nicole
    NanoPET Pharma GmbH, Germany.
    Heinke, David
    NanoPET Pharma GmbH, Germany.
    Fornara, Andrea
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Pankhurst, Quentin A.
    University College of London, UK.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Veintemillas-Verdaguer, Sabino
    CSIC Spanish National Research Council, Spain.
    Morales, Maria del Puerto
    CSIC Spanish National Research Council, Spain.
    Synthesis methods to prepare single- and multi-core iron oxide nanoparticles for biomedical applications2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 7, p. 2943-2952Article in journal (Refereed)
    Abstract [en]

    We review current synthetic routes to magnetic iron oxide nanoparticles for biomedical applications. We classify the different approaches used depending on their ability to generate magnetic particles that are either single-core (containing only one magnetic core, i.e. a single domain nanocrystal) or multi-core (containing several magnetic cores, i.e. single domain nanocrystals). The synthesis of single-core magnetic nanoparticles requires the use of surfactants during the particle generation, and careful control of the particle coating to prevent aggregation. Special attention has to be paid to avoid the presence of any toxic reagents after the synthesis if biomedical applications are intended. Several approaches exist to obtain multi-core particles based on the coating of particle aggregates; nevertheless, the production of multi-core particles with good control of the number of magnetic cores per particle, and of the degree of polydispersity of the core sizes, is still a difficult task. The control of the structure of the particles is of great relevance for biomedical applications as it has a major influence on the magnetic properties of the materials.

  • 34.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Ivanov, Zdravko G.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Kislinski, Yu V.
    Chalmers University of Technology, Sweden; Russian Academy of Sciences, Russia.
    Larsson, Peter O.
    Chalmers University of Technology, Sweden.
    A magnetic phase transition studied with high TC SQUIDs1998In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 177, p. 519-520Article in journal (Refereed)
    Abstract [en]

    We have used high-Tc SQUIDs to study the phase transition in a film of Mn3O4. The film was positioned on top of the SQUID, and the temperature of the film and the SQUID was varied in the range 30-60 K. By monitoring the voltage at the SQUID output we were able to observe a reproducable shift in the SQUID response in the range 30-50 K. This shift is related to the transition from the paramagnetic to the ferrimagnetic state of the Mn3O4 film.

  • 35.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Interaction effects in the dynamic response of magnetic liquids1991In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 101, p. 45-46Article in journal (Refereed)
    Abstract [en]

    The magnetic susceptibility of magnetic liquids has been measured for frequencies up to 70 MHz. The imaginary part of the susceptibility exhibits a maximum around 10 MHz. This feature is interpreted as due to single-particle Néel relaxation, where particle interactions cause a slight concentration dependence in the position of the maximum.

  • 36. Hanson, Maj
    et al.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Marup, S
    Comment on "Macroscopic resonant tunneling of magnetization in ferretin"1998In: Phys. Rev. Lett., Vol. 81, no 3, p. 735-Article in journal (Refereed)
  • 37.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo. Chalmers University of Technology, Sweden.
    Mörup, Steen
    Chalmers University of Technology, Sweden.
    The influence of magnetic anisotropy on the magnetization of small ferromagnetic particles1993In: Journal of Physics: Condensed Matter, ISSN 09538984, Vol. 5, p. 725-732Article in journal (Refereed)
    Abstract [en]

    The authors calculated the magnetization of small ferromagnetic particles with uniaxial anisotropy. The numerical data were compared with experimental results for a magnetic liquid consisting of small amorphous Fe 0.75C0.25 particles in decalin. From the comparison an anisotropy K approximately=3*105 J m-3 was estimated.

  • 38.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo. Chalmers University of Technology, Sweden.
    Mörup, Steen
    Chalmers University of Technology, Sweden.
    Zero-field cooled magnetization of amorphous Fe1-xCx particles - field dependence of the maximum1995In: Journal of Physics: Condensed Matter, Vol. 7, p. 9263-9268Article in journal (Refereed)
    Abstract [en]

    We measured the zero-field cooled magnetization, MZPC of a frozen magnetic liquid with amorphous Fe1-xCx particles. MZFC has a maximum at Tp approximately=20 K, which is interpreted as due to blocking of superparamagnetic relaxation in single particles. The maximum shifts towards higher temperatures with increasing measuring field. The shift is explained by the nonlinear field dependence of the magnetization of particles with a size distribution. At temperatures below Tp the magnetic particles have a coercivity and remanence in good agreement with those expected for an ensemble of non-interacting uniaxial particles with a random distribution of easy axes.

  • 39.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo. Chalmers University of Technology, Sweden.
    Nilsson, B
    Isberg, P
    Wäppling, R
    Magnetic properties of two-dimensionell arrays of epitaxial Fe (001) submicron particles1999In: J. of Appl. Phys., Vol. 85, no 5, p. 2799-Article in journal (Refereed)
  • 40.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Nilsson, Bengt A.
    Chalmers University of Technology, Sweden.
    Svedberg, Erik Björn
    Seagate Research, USA.
    Magnetic properties of epitaxial Ni (001) films sub-micron particles2001In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 236, p. 139-50Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of Ni particles with well-defined geometry, prepared by electron lithography from epitaxial Ni (001) films of thickness 50 and 60nm were studied. The particles were circles with diameters 0.6μm and rectangles with sides 0.9μm and 0.3μm, that were positioned in square and rectangular lattices, having lattice constants about twice the particle dimensions. Reference samples and particles with the lattices oriented along the [1 0 0] and [1 1 0] directions were prepared. Hysteresis curves were obtained for particles and reference samples, in the field range ±2T at temperatures between 50 and 300K. The particles were further imaged by magnetic force microscopy. The coercivities of the particles are about the same as that of the reference samples, being of the order of 10mT at room temperature and increasing with decreasing temperature. This may be explained by the temperature dependence of the magnetic anisotropy of the Ni film, estimated to K1=-12.5, -12.8 and -87.6kJm-3 at 295, 250 and 50K, respectively. Whereas the hysteresis curves of the particles are governed by the intrinsic properties of the starting film in low fields, the decreased lateral size influences the behaviour in higher fields as demagnetization effects and features characteristic for annihilation and nucleation of domain walls. One of the samples, rectangles with the long axis along the [1 1 0] direction, has a significantly higher remanence and coercivity than the others. The magnetic images show that the demagnetized state of this sample comprises both single-domain and multidomain particles. Corresponding images showed only multidomain particles in all other samples. Thus it was concluded that the actual size (0.9μm×0.3μm×50nm) is close to the critical size for single domains in Ni.

  • 41.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Pedersen, Michael S.
    Chalmers University of Technology, Sweden.
    Mörup, Steen
    Chalmers University of Technology, Sweden.
    The influence of particle size interactions on the magnetization susceptibility of nanometre-size particles1995In: Journal of Physics: Condensed Matter, ISSN 09538984, Vol. 7, p. 9269-9277Article in journal (Refereed)
    Abstract [en]

    We studied the magnetic properties of frozen magnetic liquids containing amorphous Fe1-xCx particles. By varying the particle size and concentration, we could separate single particle effects from interactions. In samples containing particles with median diameters 5.0 nm and 3.8 nm and with spontaneous saturation magnetizations 7.1 kA m-1 and 9.2 kA m -1, effects of particle interactions are observed. For 3.2 nm no interactions were observed. In samples with negligible interactions the superparamagnetic blocking temperature increases with the particle size. The effective anisotropy constant increases with decreasing particle size, implying that the anisotropy is enhanced by surface effects.

  • 42. Hendriksen, PV
    et al.
    Oxborrow, CA
    Linderoth, S
    Marup, S
    Hanson, M
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Badker, F
    Davies, K
    Swells, SW
    Particle interaction effects in systems of ultrafine iron oxide particles1993In: Nucl. Instrum. Meth. Phys. Res., Vol. 876, p. 138-Article in journal (Refereed)
  • 43.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Magnetic properties of magnetic nanoparticles in New materials for micro-scale sensors actuators : An engineering review2007In: Materials science Engineering reports, Vol. 56, no 1, p. 1-129Article in journal (Refereed)
  • 44.
    Johansson, Christer
    et al.
    RISE, Swedish ICT, Acreo, Sensor Systems.
    Ahrentorp, Fredrik
    Metod och anordning för detektering av förändringar av magnetisk respons hos magnetiska partiklar försedda med yttre skikt i bärarvätska2002Patent (Other (popular science, discussion, etc.))
  • 45.
    Johansson, Christer
    et al.
    RISE, Swedish ICT, Acreo.
    Aklint, T
    Hanson, M
    Andersson, M
    Tarras-Wahlberg, N
    Olsson, E
    Kalska, B
    Wäppling, R
    Rosen, A
    Deposited nano-metre sized iron clusters1999In: Nanostructured Materials, Vol. 12, p. 287-Article in journal (Refereed)
  • 46.
    Johansson, Christer
    et al.
    RISE, Swedish ICT, Acreo.
    Hanson, M
    Pedersen, MS
    Marup, S
    High field magnetization of magnetic liquids containing amorphous iron carbon particles1994In: J. Magn. Magn. Mat., Vol. 134, p. 25-Article in journal (Refereed)
  • 47.
    Johansson, Christer
    et al.
    RISE, Swedish ICT, Acreo.
    Hanson, M
    Pedersen, MS
    Marup, S
    Magn, J
    Magnetic properties of magnetic liquids with iron-oxide particles - the influence of anisotropy interactions1997In: J. Magn. Magn. Mat., Vol. 173, p. 5-Article in journal (Refereed)
  • 48.
    Johansson, Christer
    et al.
    RISE, Swedish ICT, Acreo.
    Hanson, Maj
    Chalmers University of Technology, Sweden.
    Influence of sample geometry in a vibrating sample magnetometer1994In: IEEE Transactions on Magnetics, Vol. 30, p. 1064-1066Article in journal (Refereed)
    Abstract [en]

    We have investigated the influence of sample size on the calibration of a vibrating sample magnetometer. As expected, when measurements and calibration are carried out on samples with the same shape the results agree within the experimental uncertainty. For two cylindrical samples of nickel, one with length and diameter 2.0 and 2.0 mm, and another with 5.3 and 1.0 mm respectively, the magnetometer signal varies with the length, in good agreement with numerical calculations.

  • 49.
    Johansson, Christer
    et al.
    RISE, Swedish ICT, Acreo. Chalmers University of Technology, Sweden; University of Gothenburg, Sweden.
    Hanson, Maj
    Chalmers University of Technology, Sweden.
    Hendriksen, Peter Vang
    DTU Technical University of Denmark, Denmark.
    Mörup, Steen
    DTU Technical University of Denmark, Denmark.
    The magnetization of magnetic liquids containing amorphous Fe1-xCx particles1993In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 122, p. 125-128Article in journal (Refereed)
    Abstract [en]

    The magnetization of amorphous Fe1-xCx particles in decalin was measured in magnetic fields up to 12 T at temperatures between 10 and 250 K. For particles with a diameter of 3.2 nm, the zero field cooled magnetization has a maximum at 20 K. This is interpreted as a blocking of the superparamagnetic relaxation of single particles.

  • 50.
    Johansson, Christer
    et al.
    RISE, Swedish ICT, Acreo.
    Hanson, Maj
    Chalmers University of Technology, Sweden.
    Lundqvist, P
    Field induced anisotropy in a magnetic liquid1996In: J. Magn. Magn. Mat., Vol. 157, p. 599-Article in journal (Refereed)
123 1 - 50 of 115
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