External magnetic field-induced mesoscopic organization of Fe ₃O₄ pyramids and carbon sheets

The current investigation is centered on the thermal decomposition of iron(II) acetyl acetonate, Fe(C₅H₇O₂) ₂, in a closed cell at 700°C, which is conducted under a magnetic field (MF) of 10 T. The product is compared with a similar reaction that was carried out without a MF. This article shows how the reaction without a MF produces spherical Fe₃O₄ particles coated with carbon. The same reaction in the presence of a 10 T MF causes the rejection of the carbon from the surface of pyramid-shaped Fe₃O₄ particles, increases the Fe₃O₄ particle diameter, forms separate carbon particles, and leads to the formation of an anisotropic (long cigarlike) orientation of Fe₃O₄ pyramids and C sheets. The macroscopic orientation of Fe₃O₄ pyramids + C sheets is stable even after the removal of an external MF. The suggested process can be used to fabricate large arrays of uniform wires comprised of some magnetic nanoparticles, and to improve the magnetic properties of nanoscale magnetic materials. The probable mechanism is developed for the growth and assembly behavior of magnetic Fe₃O₄ pyramids + C sheets under an external MF. The effect of an applied MF to synthesize morphologically different, but structurally the same, products with mesoscopic organization is the key theme of the present paper.