Chemical synthesis of nanocrystalline Ni-Zn ferrites and their magnetic characteristics

Nanocrystalline Ni1-xZnxFe2O4 powders were synthesized by the citrate precursor method, and the reaction sequence during the process was examined. Studies of the reaction sequence showed that a NiFe2O4 phase was developed as soon as the metal citric acids were thermally decomposed. In the case of ZnFe2O4, however, ZnO and Fe2O3 were produced first when the metal citric acids were decomposed at low temperature. A single phase of ZnFe2O4 was subsequently obtained when a heat treatment was conducted at 500 degrees C for 2 h. On the other hand, in order to examine the effect of particle size on magnetic characteristics of Ni Zn ferrites, nanocrystalline Ni1-xZnxFe2O4 powders with particle sizes of approximately 7, 25 and 100 nm were prepared by coprecipitation and citrate precursor methods. The magnetic characteristics of the ultrafine (7 nm) and coarse (100 nm) nanocrystalline ferrites showed distinct differences. These differences are attributed to cation disordering at the surfaces of particles, which becomes increasingly dominant as the particle size decreases.