Ferromagnetism and electrical transport in Fe-doped NiO

We report Fe-doped 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 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 similar to 6.11x10(-10) s at a lattice site.