**1.4. Sol-gel method**

The sol-gel technique is a wet low-temperature method that provides products with a perfect chemical composition and takes advantages over the others, owing to good stoichiometric control and homogeneity, short preparation time and inexpensive precursors. Furthermore, it provides nanoparticles with controlled sizes and defined morphology. Generally, for the production of multicomponent oxides, alkoxides (substituted in some cases by acetates) are put together in alcohol. In the sol-gel method water, alcohol, pH, concentration of alkoxides, and controlled temperature are required for proper hydrolysis [11].

#### **1.5. Hydrothermal method**

The hydrothermal route is a convenient wet way to produce well crystalline materials, with particles with suitably tuned size and shape. The main advantage of hydrothermal synthesis over conventional wet-chemistry methods is that it occurs under non-standard conditions, and that non-classical crystallization pathways can be explored. Many factors can be varied such as temperature, reagents ratio, solvents, and kind of salts to customize the ferrite nanoparticles [12].
