Semiconducting ${\mathrm{Ni}}_{0.4}$${\mathrm{Zn}}_{0.6}$${\mathrm{Fe}}_2$${\mathrm{O}}_4$, prepared in different ways, has been investigated. It appeared that the ac resistivity and the apparent dielectric constant of the material show a dispersion which can be explained satisfactorily with the help of a simple model of the solid: there should be well-conducting grains separated by layers of lower conductivity. Dispersion formulas are given. There is good agreement between experiment and theory.

• Received 20 March 1951

DOI:https://doi.org/10.1103/PhysRev.83.121