Classification of Ferrites, Synthesis and Properties of Spinel Ferrite Nanoparticles and Their Applications

Definition of ferrites and classification of ferrites on the basis of magnetic and crystal structures are provided. In ferrite crystal structure, Fe3+ ions can occupy tetrahedral, octahedral and trigonal bipyramid sites. When particle size decreases, their magnetization decreases. It is explained on the basis of decrease of exchange interactions as well as association of surface dangling bonds. Bulk ferromagnetic particle consists of domains and domain walls. With decrease of particle size, a single particle can attain a single domain, which can have high coercivity (Hc) as compared to that of bulk. Further decrease of particle size reduces coercivity and then it becomes zero coercivity. A particle with zero coercivity is considered as superparamagnetic particle. The different synthesis methods and many characterization techniques for spinel ferrites are mentioned. The blocking temperature (Tb) and irreversibility temperature (Tirr) for superparamgnetic particles are mentioned. The spin glass arose from magnetic particles and dilute magnetic systems are mentioned. The strain developed from decrease of particle size is mentioned.