Interpretation of microstructure dependent magnetic properties of cobalt substituted lithium ferrites

The magnetic properties of Li_0.5-x/2 Co_x Fe_2.5-x/2 O₄ (where x=0.1,0.2,0.3,0.4,0.5,0.6,0.7) ferrites have been studied. The x-ray diffraction studies reveal the single phase formation of the ferrite samples. The SEM micrographs show that the grain size decreases up to x=0.4 and increases for x>0.4. The grain size for all the samples lies in the range 0.2 μm and 6.7μm. The permeability studies at room temperature show that the values lie in the range of 5.5 to 20.6. The AC susceptibility measurements show a single domain structure. Usually the single domain structure is present in case of grain size < 0.1 μm. Both these variations suggest the presence of non- magnetic grain boundaries (NMGB) which involves deposition/ segregation of non magnetic particles over the surface of grains which reduce effective grain size. An attempt has been made to calculate the effective grain size using the data obtained from the measurements of initial permeability with temperature and the grain size obtained from the SEM micrographs.