Characterization and preparation of nanocrystalline MgCuZn ferrite powders synthesized by sol-gel auto-combustion method

Nanocrystalline Mg-Cu-Zn ferrite powders were successfully synthesized through nitrate-citrate gel auto- combustion method. Characterization of the nitrate citrate gel, as-burnt powder and calcined powders at different calcination conditions were investigated by using XRD, DTA/TG, IR spectra, EDX, VSM, SEM and TEM techniques. IR spectra and DTA/TGA studies revealed that the combustion process is an oxidation-reduction reaction in which the NO3- ion is oxidant and the carboxyl group is reductant. The results of XRD show that the decomposition of the gel indicated a gradual transition from an amorphous material to a crystalline phase. In addition, increasing the calcination temperature resulted in increasing the crystallite size of Mg-Cu-Zn ferrite powders. VSM measurement also indicated that the maximum saturation magnetization (64.1 emu/g) appears for sample calcined at 800 degrees C while there is not much further increase in M-s at higher calcination temperature. The value of coercivity field ( H-c) presents a maximum value of 182.7 Oe at calcination temperature 700 degrees C. TEM micrograph of the sample calcined at 800 degrees C showed spherical nanocrystalline ferrite powders with mean size of 36 nm. The toroidal sample sintered at 900 degrees C for 4 h presents the initial permeability (mu(i)) of 405 at 1 MHz and electrical resistivity (rho) of 1.02 x 9 10(8) Omega cm.