title: Longitudinal domain wall formation in elongated assemblies of ferromagnetic nanoparticles.
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.
authors.affiliation: Technical University of Denmark, Department of Physics, 2800 Kgs. Lyngby, Denmark.|Institut Català de Nanotecnologia, Campus UAB, 08193 Barcelona, Spain.
authors.forename: Miriam
authors.initials: M
authors.lastname: Varón
authors.affiliation: 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.
authors.forename: Marco
authors.initials: M
authors.lastname: Beleggia
authors.affiliation: Technical University of Denmark, Department of Physics, 2800 Kgs. Lyngby, Denmark.
authors.forename: Jelena
authors.initials: J
authors.lastname: Jordanovic
authors.affiliation: 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.
authors.forename: Jakob
authors.initials: J
authors.lastname: Schiøtz
authors.affiliation: Technical University of Denmark, Center for Electron Nanoscopy, 2800 Kgs. Lyngby, Denmark.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kasama
authors.affiliation: 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.
authors.forename: Victor F
authors.initials: VF
authors.lastname: Puntes
authors.affiliation: Technical University of Denmark, Department of Physics, 2800 Kgs. Lyngby, Denmark.
authors.forename: Cathrine
authors.initials: C
authors.lastname: Frandsen