Nanoscale spinel ferrites prepared by mechanochemical route

Among the many types of preparation and processing techniques, the nonconventional mechanochemical route has been recognized as a powerful method for the production of novel, high-performance, and low-cost nanomaterials. Because of their small constituent sizes and disordered structural state, nanoscale materials prepared by mechanochemical route are inherently unstable with respect to structural changes at elevated temperatures. Taking into account the considerable relevance of the thermal stability of nanoscale complex oxides to nanoscience and nanotechnology, in the present work, results on the response of mechanochemically prepared MgFe2O4 and NiFe2O4 to changes in temperature will be presented. Several interesting features are involved in the work, e.g., a relaxation of the mechanically induced cation distribution towards its equilibrium configuration, a disappearance of the superparamagnetism on heating, an increase of both the saturation magnetization and the Neel temperature with increasing particle size, and a core-shell structure of nanoparticles.