Self-assembly and flux closure studies of magnetic nanoparticle rings

Abstract

Thermoremanent magnetic nanoparticles (MNPs) can self-assemble into rings through dipolar interactions, when dispersed under appropriate conditions. Analysis of individual MNP rings and clusters by off-axis electron holography reveals bistable flux closure (FC) states at ambient temperatures, and their reversible switching by magnetic field gradients. We introduce a line-bond formalism to describe the coupling between MNPs.

Mapping magnetic fields of Fe3O4 nanosphere assemblies by electron holography

“…TEM images, as shown in Figures 3(a) interaction, although the fringing field of each dipole is unevenly distributed due to inhomogeneities of the assembly. Unlike previously reported in sub-micron scale lithographypatterned magnetic rings 15 and sub-50-nm circular assembly of magnetic nanoparticles, 10 where the magnetic flux-closure state is the dominant configuration, the Fe 3 O 4 nanosphere assembly ring does not generally show a simple magnetization state with full flux closure, instead showing a strong fringing field. One probable origin for such complicated fringing field distribution could be the irregularity of the individual particles, in which broken hollow spheres may cause branching of the induction field in 3-dimensional (3D) space.…”

“…Therefore, quantitative mapping of magnetic field in and around these nanocrystals is achievable to determine domain structures as well as stray fields. 7,8 Previous EH studies have been applied to a variety of nanoparticle systems, including magnetic bacteria, 9 cobalt, 10 iron, 11 permalloy, 12 and magnetite 13 nanoparticle assemblies. In those circumstances, the particle size is a few tens of nanometers, typically below 50 nm, and of regular shapes, such as cubes, octahedrons, and spheres, which are favorable for acquiring electron holograms and retrieving phase information.…”

Calixarene-Mediated Synthesis of Cobalt Nanoparticles: An Accretion Model for Separate Control over Nucleation and Growth

“…37,38 Calixarenes have proven to be excellent stabilizing agents of colloidal species in organic solvents, 39 and are thus well suited to support NPs at different phases of their synthesis. Complex 1 was dissolved in ODCB containing 0.33 mM C11R, and heated to temperatures from 130 °C ( t = 20 min) to 180 °C ( t = 1 h).…”

Solvothermal synthesis and characterization of cobalt microcrystals with hierarchical radial structure

“…Among magnetic metal nanoparticles, cobalt particles possess more outstanding magnetic properties and have potential applications in many areas including ferrofluids, biomedical systems, catalysts, optical and mechanic devices, high-density magnetic recording media [14][15][16][17][18][19][20][21][22][23]. The synthesis of cobalt particles with various morphologies has been reported including nanowires [24,25], nanorods [26], epitaxial film [27], platelets [28], rings [29], flowers [30] and chain-like structures [31,32]. For example, it has been reported recently that magnetic cobalt nanoparticles can selfassemble into rings through dipolar interactions, when dispersed under appropriate conditions, and show bistable flux closure states at ambient temperature [29].…”

“…The synthesis of cobalt particles with various morphologies has been reported including nanowires [24,25], nanorods [26], epitaxial film [27], platelets [28], rings [29], flowers [30] and chain-like structures [31,32]. For example, it has been reported recently that magnetic cobalt nanoparticles can selfassemble into rings through dipolar interactions, when dispersed under appropriate conditions, and show bistable flux closure states at ambient temperature [29]. Sphere-like and flower-like cobalt nanostructures with sharp petals were successfully synthesized via a facile liquid-phase reduction method [30]; while chainlike cobalt nanostructures composed of submicro spheres could be obtained with the aid of polyvinyl pyrrolidone (PVP) in ethylene glycol solution [32].…”