Reconfigurable Mechanical Anisotropy and Super-Magnetostriction in Self-Assembled Magnetic Superstructures

Our group, in collaboration with NTNU-Trondheim and the University of Sydney, is contributing to the emerging field of enhanced mechanical properties in self‐assembled superstructures of magnetic nanoparticles. In two papers recently published in the high-IF journals Advanced Functional Materials and Advanced Science, we have demonstrated how the mechanical properties of self‐assembled magnetic nanocubes can be controlled by the nanoparticle magnetocrystalline anisotropy (MA) and the superstructure shape anisotropy. A low MA‐to‐dipolar energy ratio, as found in iron oxide systems (superparamagnetic at RT), favours 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 (as that present naturally in wood) can be remotely reconfigured by means of an applied magnetic field (see left figure). 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 in the right figure here) and inspire new design rules for applied functional materials.