Size and Shape Control Synthesis of Iron Oxide–Based Nanoparticles: Current Status and Future Possibility

Magnetic phenomena at the atomic scale were discovered in the early twentieth century, whereas the discovery of the first known magnetic material (Fe3O4) revolutionized the field of magnetism. The magnetic properties of a material depend on temperature, the applied magnetic field, and pressure. A change in these variables will result in the existence of two or more forms of magnetism. Ferroand ferrimagnetic materials like Fe3O4 and some of their alloys have particles whose shape is asymmetrical when they are obtained by the grinding of bulk materials, whereas they can possess a spherical shape only when manufactured through plasma atomization or wet chemistry or when in aerosol and gas phases. Depending on the procedure used to form particles, they can be crystalline or amorphous spherical in shape. To a large extent, the synthesis process determines the degree of impurities in a particle, as well as the presence of structural defects, and, hence, the division of these defects inside the particle structure can be used to discover its magnetic properties [1, 2]. Magnetization depends on the number of unpaired valence electrons present in the atoms of solids and on the relative orientations of the neighboring magnetic moments [3]. Two types of motion of electrons in atoms are responsible for magnetism. One is the spin of electrons around the atom’s axis, and the other is the motion of electrons in an orbit around the nucleus. Iron (Fe), nickel (Ni), manganese (Mn), and cobalt (Co) are magnetic materials that have a net magnetic moment. In transition metal atoms, the magnetic moment is due to electron spin [4].