In this thesis, we have observed the exchange spring behavior in the soft (Co 0.6 Zn 0.4 Fe 2 O 4 ) - hard (SrFe 10.5 O 16.75 ) ferrite nanocomposites by tailoring the particle size of the individual phases and by suitable thermal treatment of the composites. Two phases were prepared with sol-gel method and under appropriate stoichiometry that improved magnetic properties of these two phases. XRD analysis indicates formation of pure phase for each hard, soft and nanocomposite magnetic phases. The magnetization curves for the nanocomposites heated at different temperatures show the presence of exchange spring behavior in the composite heated at 800°C and an enhancement of 53? in (BH) max compared to the parent hard ferrite (SrFe 10.5 O 16.75 ). Exchange-spring magnets are an important kashida; TEXT-ALIGN: justify; LINE-HEIGHT: 150%; TEXT-KASHIDA: 0%; TEXT-INDENT: 28.8pt; MARGIN: 0cm 0cm 0pt; mso-add-space: auto; mso-layout-grid-align: none" The interplay between the intrinsic magnetic properties and the microstructure determines both remanence and coercivity of permanent magnets. As a consequence the magnetic behaviour of permanent magnets depends sensitively on microstructural properties such as grain size, particle shape, grain boundary type, and the distribution of magnetically hard and soft phases. In order to obtain high energy products, it is necessary to increase the remanence and keep the coercive field sufficiently high. In this study, we investigate ferrite nanocomposites that composed of hard and soft magnetic phases with different concentration of hard and soft phase. Hard magnetic phase is consist of strontium ferrite nanoparticles with particle size of about 70 nm and soft magnetic phase is consist of cobalt zinc ferrite nanoparticles with particle size of about 30 nm. The magnetization curves of nanocomposites with different concentration of hard and soft phase, at room temperature shows the existence of magnetic interaction between nanoparticles in hard and soft magnetic phases.
