Self-assembled Layering of Magnetic Nanoparticles in a Ferrofluid onSilicon Surfaces

Published: January 04, 2018


Katharina Theis-Brohl, Erika C. Vreeland, Andrew Gomez, Dale L. Huber, Apurve Saini, Max Wolff, Brian B. Maranville, Erik Brok, Kathryn Krycka, Joseph A. Dura, Julie A. Borchers


This article describes the 3D self-assembly of monodisperse colloidal magnetite nanoparticles from a dilute water-based ferrofluid onto a silicon surface and the dependence of the resultant magnetic structure with applied field. The nanoparticles assemble into close-packed layers at the surface followed by more loosely-packed ones. The magnetic field dependent magnetization of the individual nanoparticle layers depends on both the rotational freedom of the layer and adjacent layers. For layers in which the nanoparticles are more free to rotate, the easy axis of the nanoparticle can readily orient along the field direction. In more dense packing, free rotation of the nanoparticles is hampered, and the nanoparticle ensembles likely build up quasi-domain states to minimize energy, which leads to lower magnetization in those layers. Detailed analysis of polarized neutron reflectometry data together with model calculations of the arrangement of the nanoparticles within the layers and input from small angle scattering measurements provide full characterization of the core/shell nanoparticle dimensions, degree of chaining, arrangement of the nanoparticles within the different layers and magnetization depth profile.
Citation: ACS Applied Materials and Interfaces
Volume: 10
Pub Type: Journals

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Magnetic nanoparticles, Self-Assembly, Neutron Reflectivity, Dipole Interactions
Created January 04, 2018, Updated June 26, 2018