Magnetic-Field-Assisted Assembly of Anisotropic Superstructures by Iron Oxide Nanoparticles and Their Enhanced Magnetism

Abstract

Magnetic nanoparticle superstructures with controlled magnetic alignment and desired structural anisotropy hold promise for applications in data storage and energy storage. Assembly of monodisperse magnetic nanoparticles under a magnetic field could lead to highly ordered superstructures, providing distinctive magnetic properties. In this work, a low-cost fabrication technique was demonstrated to assemble sub-20-nm iron oxide nanoparticles into crystalline superstructures under an in-plane magnetic field. The gradient of the applied magnetic field contributes to the anisotropic formation of micron-sized superstructures. The magnitude of the applied magnetic field promotes the alignment of magnetic moments of the nanoparticles. The strong dipole-dipole interactions between the neighboring nanoparticles lead to a close-packed pattern as an energetically favorable configuration. Rod-shaped and spindle-shaped superstructures with uniform size and controlled spacing were obtained using spherical and polyhedral nanoparticles, respectively. The arrangement and alignment of the superstructures can be tuned by changing the experimental conditions. The two types of superstructures both show enhancement of coercivity and saturation magnetization along the applied field direction, which is presumably associated with the magnetic anisotropy and magnetic dipole interactions of the constituent nanoparticles and the increased shape anisotropy of the superstructures. Our results show that the magnetic-field-assisted assembly technique could be used for fabricating nanomaterial-based structures with controlled geometric dimensions and enhanced magnetic properties for magnetic and energy storage applications.

Quantitative Analysis of the Specific Absorption Rate Dependence on the Magnetic Field Strength in ZnxFe3−xO4 Nanoparticles

“…The interest in studying the effects of pre-alignment of the MNP on their heating properties is due, among others, to the experimental observation that bacteria secreted magnetic nanoparticles—magnetosomes—have an increased heating performance, as compared to their synthetic counterparts, mainly attributable to their chain organization. This observation led several other groups to conduct studies related to the effects of the MNPs controlled assembly at the nanoscale on their hyperthermia properties [ 52 , 56 , 57 , 58 , 59 ]. In a similar attempt, in a recent previous paper, we were able to prove that the pre-alignment of MNPs in a static magnetic field ( Supplementary Figure S10 ), before their immobilization in a solid matrix, lead to an increase up to 40% in the SAR values for manganese and/or zinc ferrites in a ferrimagnetic state ( Supplementary Figure S11 ) [ 55 ].…”

Tattoos and skin barrier function: Measurements of TEWL, stratum corneum conductance and capacitance, pH, and filaggrin

“…Ferromagnetic pigments are much more powerful as electrical elements and, thus, might influence capacitance measurement even if deposited in the outer dermis. It shall also be taken into consideration that tattoo inks often contain metallic contaminants in particular nickel …”

“…It shall also be taken into consideration that tattoo inks often contain metallic contaminants in particular nickel. 35 The normal acidic skin surface pH of below 6 36 is important for the homeostasis of the skin barrier and is involved in regulating the potentially damaging proteases, and thereby directly or indirectly supporting an optimal skin barrier function. [37][38][39][40] pH is defined as freely moving hydrogen ions in watery solution.…”

Inductive Thermal Effect of Ferrite Magnetic Nanoparticles

“…The general expression of shape anisotropy constant ( K sh ) is K sh = M S 2 (N a – N c )/2 [35,103]. A predominant effect of shape anisotropy on stoichiometry, coercivity and M S values has been observed in different anisotropic magnetic nanostructures [104,105,106,107,108,109,110].…”