Transport Properties of Iron-nickel Ferrites

The mechanism of electrical conduction in the magnetic semiconductors Ni
x
Fe
3−x
O
4
with 0.6 < x ≤ 1 was investigated. The electrical properties of these compounds are extremely sensitive to the presence of α-Fe
2
O
3
as a second phase. The exponential temperature dependence of the electrical resistivity ρ and the temperature-independent thermoelectric power θ are in good agreement with an electron-hopping model. The electrical conduction occurs by thermally activated electron hopping between octahedral Fe
²⁺
and Fe
³⁺
ions with an activation energy q. The values of ρ, q and θ depend on the Fe
²⁺
concentration only, and are not sensitive to small deviations from stoichiometry due to the presence of cation or anion vacancies.