Microwave Faraday effect and conductivity in nickel ferrites and ferrite-aluminates

Nickel ferrite was prepared from pure ferric and nickel oxides by firing at temperatures between 1090 and 1350°C. The influence of the firing temperature on the Faraday effect at 3cm wavelength was studied. Results are reported for nickel ferrites with excess and deficiency of iron oxide, and for nickel ferrite-aluminates. It is shown that low loss combined with high rotation may be obtained by using a composition deficient in iron oxide and firing at a high temperature. The loss in zero field of nickel ferrite may be reduced by replacing a small proportion of the iron by aluminium. Some correlation was found between the microwave loss of these ferrites and the conductivity measured at 10Mc/s. The d.c. conductivity was also measured and compared with the a.c. conductivity.