Reconfigurable Mechanical Anisotropy in Self‐Assembled Magnetic Superstructures

Abstract

Enhancement of mechanical properties in self-assembled superstructures of magnetic nanoparticles is a new emerging aspect of their remarkable collective behavior. However, how magnetic interactions modulate mechanical properties is, to date, not fully understood. Through a comprehensive Monte Carlo investigation, this study demonstrates how the mechanical properties of self-assembled magnetic nanocubes can be controlled intrinsically by the nanoparticle magnetocrystalline anisotropy (MA), as well as by the superstructure shape anisotropy, without any need for changes in structural design (i.e., nanoparticle size, shape, and packing arrangement). A low MA-to-dipolar energy ratio, as found in iron oxide and permalloy systems, favors isotropic mechanical superstructure stabilization, whereas a high ratio yields magnetically blocked nanoparticle macrospins which can give rise to metastable superferromagnetism, as expected in cobalt ferrite simple cubic supercrystals. Such full parallel alignment of the particle moments is shown to induce mechanical anisotropy, where the superior high-strength axis can be remotely reconfigured by means of an applied magnetic field. The new concepts developed here pave the way for the experimental realization of smart magneto-micromechanical systems (based, e.g., on the permanent super-magnetostriction effect illustrated here) and inspire new design rules for applied functional materials.Self-assembly of magnetic nanoparticles of different sizes and shapes has been successfully applied to design superstructured materials of novel morphologies, including helices, rods, stripes, supercubes, and labyrinths. [1][2][3][4] Such magnetic superstructures

Using small-angle scattering to guide functional magnetic nanoparticle design

“…34 Nowadays, the synthesis of supraparticles or mesocrystals can be well controlled 35 allowing the preparation of particle systems with a wide range of magnetic properties and additional functionalities. 36 In addition to the synthesis of complex, multifunctional particle systems, the shape and size of the individual nanocrystals can be easily controlled for many materials, 37 including iron oxides magnetite/maghemite, 38 and hematite. 39 This allows the preparation of shape anisotropic nanoparticles, which are great candidates for various applications as the magnetic properties can be controlled by particle morphology.…”

Using small-angle scattering to guide functional magnetic nanoparticle design

“…33 It is worth mentioning that supraparticles are well-suited for magnetic separation and also envisioned for a wide array of applications related to sustainability. 34 Nowadays, the synthesis of supraparticles or mesocrystals can be well controlled 35 allowing the preparation of particle systems with a wide range of magnetic properties and additional functionalities 36 .…”

Little Adjustments Significantly Simplify the Gram-Scale Synthesis of High-Quality Iron Oxide Nanocubes

“…Simulations revealed that magnetic interactions result in an increase of up to 45% in cohesive energy and, thereby, significantly enhance the mechanical properties . Moreover, the mechanical properties of the nanoparticle assembly can be controlled by the magnetocrystalline anisotropy of the nanoparticles and shape anisotropy of the assembly, resulting in isotropic or anisotropic mechanical properties …”

“…16 Moreover, the mechanical properties of the nanoparticle assembly can be controlled by the magnetocrystalline anisotropy of the nanoparticles and shape anisotropy of the assembly, resulting in isotropic or anisotropic mechanical properties. 17 For the synthesis of cubic iron oxide nanoparticles, several different approaches have been published over the past two decades. To obtain highly crystalline nanoparticles with control over size, size distribution, and shape, usually the thermal decomposition of suitable iron precursors is the method of choice.…”