Metal@SiO2 Core–Shells with Self-Arrested Migrating Core

Developing easy and customizable strategies for the directional structure modulation of multicomponent nanosystems to influence and optimize their properties are a paramount but challenging task in nanoscience. Here, we demonstrate highly controlled eccentric off-center positioning of metal–core in metal@silica core–shells by utilizing an in situ generated biphasic silica-based intraparticle solid–solid interface. In the synthetic strategy, by including Ca2+-ions in silica–shell and successive oxidative and reductive annealing at high temperature, a unique hairline–biphasic interface is evolved via the heat-induced concentric radial segregation of calcium silicate phase at the interior and normal silica phase at the exterior of core–shell, which can effectively arrest the outwardly migrating metal–core within rubbery calcium silicate phase, affording various eccentric core–shells, where core-positions are flexibly controlled by the annealing time and amounts of initially added Ca2+-ions. In the structure–property correlation study, the strategy allows fine-tuning of dipolar interaction-based blocking temperatures and magnetic anisotropies of different eccentric core–shells as the function of variable off-center distance of magnetic core without changing the overall size of nanoparticles. This work demonstrates the discovery and potential application of biphasic solid–solid media interface in controlling the heat-induced migration of metal nanocrystals and opens the avenues for exploiting the rarely studied high-temperature solid-state nanocrystal conversion chemistry and migratory behavior for directional nanostructure engineering.