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Varón M, Beleggia M, Jordanovic J, Schiøtz J, Kasama T, Puntes VF, Frandsen C. Longitudinal domain wall formation in elongated assemblies of ferromagnetic nanoparticles. Sci Rep 2015; 5:14536. [PMID: 26416297 PMCID: PMC4586724 DOI: 10.1038/srep14536] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 08/21/2015] [Indexed: 11/09/2022] Open
Abstract
Through evaporation of dense colloids of ferromagnetic ~13 nm ε-Co particles onto carbon substrates, anisotropic magnetic dipolar interactions can support formation of elongated particle structures with aggregate thicknesses of 100-400 nm and lengths of up to some hundred microns. Lorenz microscopy and electron holography reveal collective magnetic ordering in these structures. However, in contrast to continuous ferromagnetic thin films of comparable dimensions, domain walls appear preferentially as longitudinal, i.e., oriented parallel to the long axis of the nanoparticle assemblies. We explain this unusual domain structure as the result of dipolar interactions and shape anisotropy, in the absence of inter-particle exchange coupling.
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Affiliation(s)
- Miriam Varón
- Technical University of Denmark, Department of Physics, 2800 Kgs. Lyngby, Denmark.,Institut Català de Nanotecnologia, Campus UAB, 08193 Barcelona, Spain
| | - Marco Beleggia
- Technical University of Denmark, Center for Electron Nanoscopy, 2800 Kgs. Lyngby, Denmark.,Helmholtz-Zentrum-Berlin fuer Materialen und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Jelena Jordanovic
- Technical University of Denmark, Department of Physics, 2800 Kgs. Lyngby, Denmark
| | - Jakob Schiøtz
- Technical University of Denmark, Department of Physics, 2800 Kgs. Lyngby, Denmark.,Danish National Research Foundation Center for Individual Nanoparticle Functionality, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Takeshi Kasama
- Technical University of Denmark, Center for Electron Nanoscopy, 2800 Kgs. Lyngby, Denmark
| | - Victor F Puntes
- Institut Català de Nanotecnologia, Campus UAB, 08193 Barcelona, Spain.,Vall d'Hebron Institut de Recerca (VHIR), 08035, Barcelona, Spain.,Institut Català de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
| | - Cathrine Frandsen
- Technical University of Denmark, Department of Physics, 2800 Kgs. Lyngby, Denmark
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Varón M, Ojea-Jimenez I, Arbiol J, Balcells L, Martínez B, Puntes VF. Spontaneous formation of hollow cobalt oxide nanoparticles by the Kirkendall effect at room temperature at the water-air interface. Nanoscale 2013; 5:2429-2436. [PMID: 23399978 DOI: 10.1039/c2nr32657d] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We observe the spontaneous formation of hollow cobalt oxide nanoparticles at room temperature, indicating an enhancement of the solid-state diffusion at the nanoscale. Single crystal cobalt nanoparticles covered by a hydrophobic organic layer were transformed spontaneously into CoO hollow nanoparticles when deposited on the water-air interface in a matter of a few hours. The presence of water modifies the reactivity on the nanoparticle surface favoring the formation of the hollow structure; otherwise Co-CoO core-shell nanoparticles are obtained. The CoO hollow nanoparticles are formed only in an intermediate state, and after a period of time these structures finally undergo disintegration to form minor CoO entities.
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Affiliation(s)
- Miriam Varón
- Catalan Institute of Nanotechnology-ICN, Campus de la UAB, Edifici Q-ETSE, 08193 Bellaterra, Barcelona, Spain
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Varón M, Beleggia M, Kasama T, Harrison RJ, Dunin-Borkowski RE, Puntes VF, Frandsen C. Dipolar magnetism in ordered and disordered low-dimensional nanoparticle assemblies. Sci Rep 2013; 3:1234. [PMID: 23390584 PMCID: PMC3565170 DOI: 10.1038/srep01234] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2012] [Accepted: 01/18/2013] [Indexed: 11/14/2022] Open
Abstract
Magnetostatic (dipolar) interactions between nanoparticles promise to open new ways to design nanocrystalline magnetic materials and devices if the collective magnetic properties can be controlled at the nanoparticle level. Magnetic dipolar interactions are sufficiently strong to sustain magnetic order at ambient temperature in assemblies of closely-spaced nanoparticles with magnetic moments of ≥ 100 μB. Here we use electron holography with sub-particle resolution to reveal the correlation between particle arrangement and magnetic order in self-assembled 1D and quasi-2D arrangements of 15 nm cobalt nanoparticles. In the initial states, we observe dipolar ferromagnetism, antiferromagnetism and local flux closure, depending on the particle arrangement. Surprisingly, after magnetic saturation, measurements and numerical simulations show that overall ferromagnetic order exists in the present nanoparticle assemblies even when their arrangement is completely disordered. Such direct quantification of the correlation between topological and magnetic order is essential for the technological exploitation of magnetic quasi-2D nanoparticle assemblies.
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Affiliation(s)
- M Varón
- Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
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Amigo JM, Bastús NG, Hoen R, Vázquez-Campos S, Varón M, Royo M, Puntes V. Analysis of time-dependent conjugation of gold nanoparticles with an antiparkinsonian molecule by using curve resolution methods. Anal Chim Acta 2010; 683:170-7. [PMID: 21167967 DOI: 10.1016/j.aca.2010.10.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Revised: 10/11/2010] [Accepted: 10/12/2010] [Indexed: 11/27/2022]
Abstract
In this work, the time-dependent conjugation process between a thiolated molecule (with anti-parkinsonian properties) and gold nanoparticles has been monitored and studied by the combined use of fast acquisition Ultra Violet-Visible (UV-Vis) spectra and the ability of Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) technique. From the highly informative kinetic profiles obtained it was possible to extract quantitative and qualitative information of the conjugation process which includes i) time-dependent concentration profiles and pure spectra of species involved on conjugation process, ii) estimation of molecule concentration necessary for the completeness of the conjugation reaction, iii) molecule footprint and iv) free energy of molecule adsorption.
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Affiliation(s)
- José Manuel Amigo
- Department of Food Science, Quality & Technology, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Copenhagen, Frederiksberg C, Denmark.
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Varón M, Peña L, Balcells L, Skumryev V, Martinez B, Puntes V. Dipolar driven spontaneous self assembly of superparamagnetic Co nanoparticles into micrometric rice-grain like structures. Langmuir 2010; 26:109-116. [PMID: 20038165 DOI: 10.1021/la902169s] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Superparamagnetic single crystal single domain Co nanoparticles of 6 nm in diameter evaporated onto highly pyrolytic oriented graphite spontaneously self-assemble into super structures with an elongated shape. These structures have been studied by optical and scanning electron microscopies, atomic and magnetic force microscopy, electron dispersive X-ray analysis, and SQUID magnetometry. We propose that the weak dipolar interactions between superparamagnetic dipoles of the cobalt nanoparticles are responsible for the formation of these structures when the dipolar magnetic interactions are strong enough to influence the general process of self-assembly dominated by van der Waals forces between neighboring nanoparticles and between nanoparticles and the substrate during evaporation of the solvent.
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Affiliation(s)
- Miriam Varón
- Institut Catala de Nanotecnologia, Campus UAB, 08193 Barcelona, Spain
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