Magnetically Induced Anisotropic Interaction in Colloidal Assembly

Abstract

The wide accessibility to nanostructures with high uniformity and controllable sizes and morphologies provides great opportunities for creating complex superstructures with unique functionalities. Employing anisotropic nanostructures as the building blocks significantly enriches the superstructural phases, while their orientational control for obtaining long-range orders has remained a significant challenge. One solution is to introduce magnetic components into the anisotropic nanostructures to enable precise control of their orientations and positions in the superstructures by manipulating magnetic interactions. Recognizing the importance of magnetic anisotropy in colloidal assembly, we provide here an overview of magnetic field-guided self-assembly of magnetic nanoparticles with typical anisotropic shapes, including rods, cubes, plates, and peanuts. The Review starts with discussing the magnetic energy of nanoparticles, appreciating the vital roles of magneto-crystalline and shape anisotropies in determining the easy magnetization direction of the anisotropic nanostructures. It then introduces superstructures assembled from various magnetic building blocks and summarizes their unique properties and intriguing applications. It concludes with a discussion of remaining challenges and an outlook of future research opportunities that the magnetic assembly strategy may offer for colloidal assembly.

Anisotropy in magnetic materials for sensors and actuators in soft robotic systems

“…where K n (n = 0, 1, 2, 3…) is the n-th magnetocrystalline anisotropy constant, and θ is the angle between the magnetization and the c-axis of the hexagonal system. 22 Generally, K 0 is disregarded since it is an isotropic value. hcp-Co has a K 1 of 4.5 Merg cm −3 and K 2 of 1.5 Merg cm −3 .…”

“…Thus, fine-tuning the apparent shape of magnetic materials by adjusting the aspect ratio leads to changes in the magnetic properties, representatively coercivity and remanence. 22 The size of the magnetic materials is another key factor affecting the magnetic properties and even contributes to magnetic anisotropy, specifically with a decrease in dimensions (Fig. 4c and d).…”

“…4d). 22,35,36 Because of their high surface-to-volume ratio arising from the nanosize effect, magnetic NPs (MNPs) typically exhibit lower M s values.…”

Magnetic Assembly of Eu-Doped NaYF4 Nanorods for Field-Responsive Linearly and Circularly Polarized Luminescence

“…As a nontemplate approach, magnetic assembly has been widely employed for organizing nanoscale building blocks into diverse superstructures with controllable symmetries and phases. − It features many advantages, including instantaneous and reversible action, contactless operation, and the directional nature of magnetic interactions. ,− Recent studies have further revealed that the magnetic field can be configured as uniform or chiral depending on the spatial arrangement of magnets, enabling the creation of chiral superstructures through the magnetic assembly approach. − Applying this approach to luminescent nanostructures is therefore expected to produce superstructures featuring polarized emission with dynamic tunability offered by the convenient manipulation of the strength and direction of the magnetic field.…”

Dual-Responsive Fe3O4@Polyaniline Chiral Superstructures for Information Encryption

“…Magnetic field-guided self-assembly provides rapid, reversible, and remote modulation of magnetic nanoparticles into reconfigurable superstructures across large areas. 19,20 It has been shown that magnetic fields can be configured to induce chirality in magnetic particle assemblies. 21 We have further demonstrated that a gradient magnetic field is intrinsically chiral, allowing the assembly of magnetic nanoparticles into chiral superstructures with reversible field-dependent tunability.…”