Magneto-responsive Chain-like Arrangements of Size-tuned and Cobalt-doped Ferrites derived from Silica-encapsulated Precursors

Herein, the aqueous synthesis of magneto-responsive nanostructures, i.e., chain-like arrangements built from truncated cubic cobalt-doped ferrite particles, is reported. The magnetic nanoparticles (CoxFe3-xO4, 0.40 x 0.51) are synthesized in an eco-friendly manner via hydrothermal conversion of antiferromagnetic -FeOOH nanorods, which were surface-modified prior with sodium polyacrylate (PAA) and a surrounding silica shell. The silica layers are formed in different thicknesses through a Stöber sol-gel process that effectively encapsulates the PAA-stabilized nanorods. Subsequently, cobalt ferrite's formation was confirmed through X-ray diffraction and elemental analysis. A distinct relationship emerged between the cobalt-to-iron ratio (0.16 to 0.20) and nanoparticle dimensions (14 to 47 nm), revealing that both parameters increase with silica shell thickness and reaction temperature. In contrast, deviations in crystallite size were observed based on PAA presence. Magnetic property analysis showcased hysteresis behavior, emphasizing enhanced magnetization up to 91 Am²/kg with larger nanoparticles. Furthermore, this approach provides the dependency of the silica layer thickness on the formation of nanochains. When an external field is applied, the randomly distributed particles orient themselves into nanochains, facilitating the determination of the number of particles in both parallel and perpendicular orientations calculated from Small-Angle X-ray Scattering analysis. It is observed that the cluster numbers vary in comparison to the dipole-dipole interaction energy and size of particles due to the formation of these chain-like structures and bundles. Thus, this study illustrates the complex interplay between synthesis parameters and nanoparticle formation mechanisms and highlights their potential applications in biomedicine and nanotechnology.