  We fabricated NiFe2O thin films on MgAl2O4 (001) substrates by reactive dc
magnetron co-sputtering in a pure oxygen atmosphere at different substrate
temperatures. The film properties were investigated by various techniques with
a focus on their structure, surface topography, magnetic characteristics, and
transport properties. Structural analysis revealed a good crystallization with
epitaxial growth and low roughness and a similar quality as in films grown by
pulsed laser deposition. Electrical conductivity measurements showed high room
temperature resistivity (12 Ohmm), but low activation energy, indicating an
extrinsic transport mechanism. A band gap of about 1.55 eV was found by optical
spectroscopy. Detailed x-ray spectroscopy studies confirmed the samples to be
ferrimagnetic with fully compensated Fe moments. By comparison with multiplet
calculations of the spectra we found that the cation valencies are to a large
extent Ni2+ and Fe3+.
