**4. Conclusion**

We have succeeded in fabricating spinel ferrite nanoparticles such as zinc ferrite (ZnFe2O4), manganese ferrite (MnFe2O4) and nickel ferrite (NiFe2O4) nanocrystals by a thermal treatment method utilizing only metal nitrates and as precursors, deionized water as a solvent and PVP as a capping agent.PVP played three crucial roles in synthesizing spinel ferrite nanoparticles, i.e., (1) the control of the growth of the nanoparticles; (2) the prevention of agglomeration of the nanoparticles; and (3) the production of nanoparticles that have a uniform distribution of shapes. The average particle sizes of metal ferrite nanoparticles were determined by TEM which increased with the calcinations temperature and they had good agreement with XRD results. FT-IR confirmed the presence of metal oxide bands at all temperatures and the absence of organic bands at 873 K for zinc and manganese ferrite nanoparticles and at 723 K for the nickel ferrite nanoparticles.VSM results demonstrated that zinc and manganese ferrite nanoparticles displayed super paramagnetic behaviors while nickel ferrite nanoparticles exhibited ferromagnetic behaviors. The present study also substantiated that, in ferrites, the values of the quantities that were acquired by VSM, such as saturation magnetization and coercivity field, are primarily dependent on the methods of preparation of the ferrites. This simple method, which is cost-effective and environmentally friendly, produces no toxic byproducts and can be used to fabricate pure, crystalline spinel metal ferrite nanocrystals.

Furthermore, this method can be extended to the synthesis of other spinel ferrite nanoparticles of interest.

## **5. References**

376 Advances in Crystallization Processes

to a mixed spinel structure [65].Figure 27 (right) shows the expanded coercivity field (Hc) of region around of origin for clear visibility at room temperature in the range of approximately –400 to +400 Oe. The coercivity field values are listed in Table 4. These variations are not similar with saturation magnetization because, when the particle size increases from 15 to 69 nm, the coercivity field decreases from 150 to 32 Oe at room temperature. Variations of the coercivity field with particle size of nickel ferrite nanoparticles can be elucidated on the basis of domain structure, critical size, and the

Finaly, It is worth noting that the magnetic properties of similar ferrite nanoparticles of the same particle size differ depending on the preparation method used. Table 5 shows some literature values of Ms and Hc that were measured at similar conditions for some spinel ferrite nanoparticles. The data show that the pairs of similar spinel ferrite nanoparticles of the same particle size have different saturation magnetization values and coercivity fields. The results indicate that, in fact, the magnetic properties of ferrites are related primarily to

> Saturation magnetization Ms (emu/g)

4 1.4 32.1 11.9 77 30

Table 5. Magnetic properties of some spinel ferrite nanoparticles reported in the literatures which were measured at room temperature in range of approximately −10 to +10 kOe.

We have succeeded in fabricating spinel ferrite nanoparticles such as zinc ferrite (ZnFe2O4), manganese ferrite (MnFe2O4) and nickel ferrite (NiFe2O4) nanocrystals by a thermal treatment method utilizing only metal nitrates and as precursors, deionized water as a solvent and PVP as a capping agent.PVP played three crucial roles in synthesizing spinel ferrite nanoparticles, i.e., (1) the control of the growth of the nanoparticles; (2) the prevention of agglomeration of the nanoparticles; and (3) the production of nanoparticles that have a uniform distribution of shapes. The average particle sizes of metal ferrite nanoparticles were determined by TEM which increased with the calcinations temperature and they had good agreement with XRD results. FT-IR confirmed the presence of metal oxide bands at all temperatures and the absence of organic bands at 873 K for zinc and manganese ferrite nanoparticles and at 723 K for the nickel ferrite nanoparticles.VSM results demonstrated that zinc and manganese ferrite nanoparticles displayed super paramagnetic behaviors while nickel ferrite nanoparticles exhibited ferromagnetic behaviors. The present

Coercivity field Hc (Oe)

Negligible 156 59

Negligible 2000-2700 Negligible References

[68] [37] [69] [70] [71] [72]

Average particle size (nm)

anisotropy of the crystal [16, 66-67].

the methods used to prepare them.

method

gel Sol gel

Combustion Modified sol

Coprecipitation Mechanic alloying Hydrothermal

**Specimens** Preparation

**ZnFerrite ZnFerrite NiFerrite NiFerrite CoFerrite CoFerrite** 

**4. Conclusion** 


Crystalization in Spinel Ferrite Nanoparticles 379

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**Section 4** 

**Bulk Crystallization from Aqueous Solutions** 

