**Abstract**

The scope of this chapter is to get deeper insight into the correlation between synthesis parameters and magnetic behavior of the nanocomposite materials containing hematite (α-Fe2O3) nanoparticles. Potential applications of nanohematite in biomedicine are listed in the short overview. Then, basic requirements necessary for synthesis of high-quality nanoparticles for biomedical application are summarized. The next part of the chapter is devoted to the sol-gel synthesis that is recognized as suitable for preparation of the nanocomposite materials containing α-Fe2O3 nanoparticles. Having in mind that sol-gel method considers preparation of hematite nanoparticles via Fe2O3 phase transformations initiated by thermal treatment at high temperatures, coexistence of the other iron oxides (such as ε-Fe2O3) with α-Fe2O3 phase is commented. Special attention is paid on mechanism of the critical field (which is in literature usually denoted as coercivity field) alterations. Diffraction patterns and hysteresis measurements of the chosen samples containing hematite nanoparticles in the silica matrix are represented. Finally, variations in the observed measured critical field values are discussed.

**Keywords:** nano α-Fe2O3-phase, nano ε-Fe2O3-phase, silica, synthesis parameters, intrinsic coercivity field, biomedical application
