The effect of heat-treatment on the Curie temperature of CuZn-ferrite and Cu-ferrite is investigated. The ferrite samples were prepared from metal oxides by ordinary sintering techniques.
For CuZn-ferrite the Curie temperatures were measured on specimens annealed in air and oxygen atmosphere at temperatures between 600℃ and 1100℃. For Cu-ferrite the annealing temperature range was between 450℃ and 1100℃ in air, oxygen and nitrogen atmospheres.
The Curie temperatures of CuZn-ferrite and Cu-ferrite were determined from the observed temperature dependence of the magnetic permeability and magnetization, respectively.
Both in CuZn-ferrite and Cu-ferrite the observed Curve temperature decreases with increasing annealing temperature up to about 900℃. This is attributed to the thermal disordering of the $Cu^{2+}$ ion distribution. For annealing temperatures close to 970℃, the Curie temperatures increase anomalously. This newly observed effect cannot be unambiguously explained by reduction of $Cu^{2+}$ ion to $Cu^+$, although close to 1100℃ the specimens annealed in oxygen atmosphere show higher Curie temperatures than those annealed in air.
The kinetics of cation redistribution of Cu-ferrite is also investigated. The activation energy of cation migration is estimated to be 0.65 $\pm$ 0.05 eV per atom.
