Abstract
The effects of adding transition metals (Ni and Co) on the optical and electrical properties of four thin films Ni~1.25~Fe~1.5~Ge~0.25~O~4~, Ni~1.5~Fe~1~Ge~0.5~O~4~, Co~1~Fe~1~Ge~0.5~O~4~ and Co~1.25~Fe~1.5~Ge~0.25~O~4~ are reported. X‐ray diffraction was used to ascertain the amorphization nature of the deposited films. The optical absorption behavior of these films was studied from the transmission and reflection in the range 200–1100 nm. It was found that the optical band gap increases on increasing GeO~2~ and arises from direct forbidden transitions. The opposite trend was found with the band tail width of the localized state. Optical constant parameters such as refractive index and absorption index were obtained for the films. The results for the alternating‐current (ac) conductivity and the dielectric constant of the four films are presented over the temperature range 277–357 K and the frequency range 0.1 to 1000 kHz. The ac conductivity increases with temperature and frequency and decreases with the increase in Ni^2+^ or Co^2+^ content. The effect of composition and temperature on the dielectric constant was also studied. The frequency variation of the dielectric constant does not have a peak, unlike many semiconductor glasses. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)