title: Size and property bimodality in magnetic nanoparticle dispersions: single domain particles vs. strongly coupled nanoclusters.
abstract: The widespread use of magnetic nanoparticles in the biotechnical sector puts new demands on fast and quantitative characterization techniques for nanoparticle dispersions. In this work, we report the use of asymmetric flow field-flow fractionation (AF4) and ferromagnetic resonance (FMR) to study the properties of a commercial magnetic nanoparticle dispersion. We demonstrate the effectiveness of both techniques when subjected to a dispersion with a bimodal size/magnetic property distribution: i.e., a small superparamagnetic fraction, and a larger blocked fraction of strongly coupled colloidal nanoclusters. We show that the oriented attachment of primary nanocrystals into colloidal nanoclusters drastically alters their static, dynamic, and magnetic resonance properties. Finally, we show how the FMR spectra are influenced by dynamical effects; agglomeration of the superparamagnetic fraction leads to reversible line-broadening; rotational alignment of the suspended nanoclusters results in shape-dependent resonance shifts. The AF4 and FMR measurements described herein are fast and simple, and therefore suitable for quality control procedures in commercial production of magnetic nanoparticles.
authors.affiliation: Solid State Physics, Department of Engineering Sciences, Ångström Laboratory, Uppsala University, Sweden. erik.wetterskog@angstrom.uu.se.
authors.forename: E
authors.identifier: http://orcid.org/0000-0002-6681-4803
authors.initials: E
authors.lastname: Wetterskog
authors.affiliation: SOLVE Research and Consultancy AB, Lund, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Castro
authors.affiliation: Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Zeng
authors.affiliation: SP Chemistry, Materials and Surfaces, SP Technical Research Institute of Sweden, Borås, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Petronis
authors.affiliation: nanoPET Pharma GmbH, Berlin, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Heinke
authors.affiliation: Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Olsson
authors.affiliation: SOLVE Research and Consultancy AB, Lund, Sweden and Lund Centre for Field-Flow Fractionation, Department of Food Technology, Engineering and Nutrition, Lund University, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Nilsson
authors.affiliation: nanoPET Pharma GmbH, Berlin, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Gehrke
authors.affiliation: Solid State Physics, Department of Engineering Sciences, Ångström Laboratory, Uppsala University, Sweden. erik.wetterskog@angstrom.uu.se.
authors.forename: P
authors.initials: P
authors.lastname: Svedlindh