Abstract
NiFe2O4 (NFO) thin films were deposited on quartz substrates by rf
magnetron sputtering, and the influence of the deposition conditions on their physicchemical
properties was studied. The films structure and the high temperature transport
properties were analyzed as a function of the deposition temperature. The analysis of the
total conductivity up to 800 °C in different pO2 containing atmospheres showed a distinct
electronic behavior of the films with regard to the bulk NFO material. Indeed, the thin films
exhibit p-type electronic conductivity, while the bulk material is known to be a prevailing ntype
electronic conductor. This difference is ascribed to the dissimilar concentration of Ni3+
in the thin films, as revealed by XPS analysis at room temperature. The bulk material with a
low concentration of Ni3+ (Ni3+/Ni2+ ratio of 0.20) shows the expected n-type electronic
conduction via electron hopping between Fe3+−Fe2+. On the other hand, the NFO thin films
annealed at 800 °C exhibit a Ni3+/Ni2+ ratio of 0.42 and show p-type conduction via hole
hopping between Ni3+−Ni2+.
