Study of Self-Assembly of Octahedral Magnetite under an External Magnetic Field

In order to study the self-assembly of octahedral magnetite (Fe 3 O 4 ) under external magnetic fields, the octahedral magnetite with high crystallization was synthesized through a solvothermal process. When the concentration of NaOH was adjusted from 0 to 3.0 mol/L, the shape of Fe 3 O 4 particles was transformed from 3-D self-assembly sphere to truncated octahedron and finally to octahedron. Previous studies have showed that magnetite chains can be formed when an external magnetic field was applied during the reaction process. Here we study the self-assembly of magnetite octahedrons under an external magnetic field and find that these octahedrons can also form chains, mainly along the ⟨111⟩ direction—one of its two easy magnetic axes—rather than the other axis ⟨110⟩ direction. This fact indicates that particle morphology can significantly influence their assembly mechanism besides the directions of easy-magnetic axis.