We report Fe-doped $\mathrm{NiO}$ nanopowder, exhibiting room ferromagnetism mainly arising from the double exchange mechanism through the doped Fe ions and free charge carriers. Electrical measurements reveal that ac conductivity of the polycrystalline ceramics with Fe-doped $\mathrm{NiO}$ can be expressed as the sum of a frequency-independent conductivity ${\sigma }_1$ and a frequency-dependent one ${\sigma }_2$. The latter ${\sigma }_2$ can be represented by the frequency dispersion for the dielectric loss due to the hopping diffusion of charge carriers with a single effective staying time $\tau \sim 6.11\times {10}^{-10}\mathrm{s}$ at a lattice site.

• Received 18 January 2006

DOI:https://doi.org/10.1103/PhysRevB.73.193308