Structural and magnetic properties of Zn-substituted cobalt ferrites prepared by co-precipitation method

Zn substituted cobalt ferrite spinels with the general formula ZnxCo1-xFe2O4 (with x varying from 0 to 0.5) were synthesized by a co-precipitation method and calcined at 500 degrees C and 800 degrees C. It was found that Zn substitution has a big effect in decreasing the Curie temperature (T-c), from around 440 degrees C for the undoped sample to similar to 180 degrees C with x = 0.5. However, these values were also strongly affected by the pre-calcination temperature of the samples, thus T-C shifts from similar to 275 degrees C for the x = 0.3 sample to similar to 296 degrees C after calcination at 500 degrees C and 800 degrees C respectively. These effects are due to facilitation of demagnetisation by substitution of the non-magnetic Zn ions and by production of very small nanoparticles. The latter are removed by higher temperature calcinations and so T-C increases.