Structural and transport properties of stoichiometric and Cu2+-doped magnetite: Fe3−xCuxO4

The Cu substituted magnetites Fe3−xCuxO4 (x = 0, 0.01, 0.2, and 1.0) were prepared by solid-state reaction route. The X-ray diffraction measurements confirm the cubic spinel structure of all doped samples of Fe3−xCuxO4. Resistivity measurements have been made in the range 77 K < T < 300 K. The polycrystalline samples for the lower compositions (x = 0.0 and 0.01) exhibit the first order phase transition at the Verwey transition Tv = 123 (119) K. No transitions were seen for samples with higher doping concentration (x = 0.2 and 1.0). The structural aspects of Cu substituted magnetites are further investigated by Raman spectra. The spectrum reveals five Raman active modes at room temperature consistent with the previous Raman spectra. The changes in Raman spectrum as functions of Cu doping concentration are gradual. However, the Raman active mode for parent Fe3O4 at ≅670 cm−1 is shifted at ≅660 cm−1 for over doped Fe2CuO4, inferring that Cu2+ ions are located mostly on the octahedral (B) sites. The transmission Mössbauer spectroscopy was used to determine the site preference of the substitutions and their effect on the hyperfine magnetic fields which confirms that for copper ferrite: Fe2CuO4 the Cu2+ ions are located mostly on the octahedral (B) sites of the spinel structure.