**2. Ferrites and their structural symmetries**

Among the magnetic materials that have found broad practical application in technology, ferrites deserve attention. Ferrite nanoparticles are the most explored magnetic nanoparticles up to date. They are widely used in high-frequency applications, because an AC field does not induce undesirable eddy currents in an insulating material [3,4].To increase the recorded information density, it seems reasonable to obtain nanocrystalline

Crystalization in Spinel Ferrite Nanoparticles 351

Fig. 1. Schematic of two subcells of a unit cell of the spinel structure, showing octahedral

Fig. 2. Interionic distances in the spinel structure for the different types of lattice site

According to the distribution of cations, there are normal, mixed and inversed spinels structures which depended on the fact what kind of ions and in what order A and B take empty spaces. In this review, we will investigate zinc ferrite (ZnFe2O4), manganese ferrites (MnFe2O4) and nickel ferrite (NiFe2O4) from normal, mixed and inverse structures

and tetrahedral sites.

interactions

respectively [12].

ferrites and to prepare magnetic carriers based on them. Ferrites have three different structural symmetries: garnet, hexagonal and cubic which are determined by the size and charge of the metal ions that balance the charge of the oxygen ions, and their relative amounts [5]. In this review, the focus will be on spinel ferrites nanocrystals because, they are regarded as two of the most important inorganic nanomaterials because of their electronic, optical, electrical, magnetic, and catalytic properties.Moreover, the majority of the important ferrite are spinel ferrite [6].
