**3.1.1 Process of fabrication of metal ferrite nanocrystals**

In this study, metal nitrate reagents, poly (vinyl pyrrolidon) (PVP), and deionized water were used as precursors. In addition, a capping agent to control the agglomeration of the particles and a solvent were used. Iron nitrate, Fe(NO3)39H2O, zinc nitrate, Zn(NO3)26H2O, nickel nitrate, Ni(NO3)26H2O , and manganese nitrate Mn(NO3)26H2O , were purchased from Acros Organics with a purity exceeding 99%. PVP (MW = 29000) was purchased from Sigma Aldrich and was used without further purification. An aqueous solution of PVP was prepared by dissolving polymer in deionized water at 363 K, before mixing 0.2 mmol iron nitrate and 0.1 mmol metal nitrate (Fe:M = 2:1) into the polymer solution and constantly stirring for 2 h using a magnetic stirrer until a colorless, transparent solution was obtained. The mixed solution was poured into a glass Petri dish and heated at 353 K in an oven for 24 h to evaporate the water. The dried, orange, solid zinc ferrite that remained was crushed and ground in a mortar to form powder. The calcinations of the powders were conducted at 723, 773, 823, and 873 K for 3 h for the decomposition of organic compounds and the crystallization of the nanocrystals. The processing steps employed separately for the synthesis of each ferrite nanoparticles.
