Structural and transport properties of stoichiometric Mn2+-doped magnetite: Fe3−xMnxO4

The polycrystalline samples of Fe3−xMnxO4 (0.10 ≤ x ≤ 0.50) were prepared by a solid-state route reaction method. X-ray diffraction pattern shows that Mn2+ doped magnetites are in single phase and possess cubic inverse spinel structure. The resistivity measurements (10 < T < 300 K) for x = 0.0 and 0.01 confirms the first order phase transition at the Verwey transition TV = 123 K and 117 K, respectively. No first order phase transition was evidenced for Fe3−xMnxO4 (0.10 ≤ x ≤ 0.50). Small polaron model has been used to fit the semiconducting resistivity behavior and the activation energy ɛa, for samples x = 0.10 and 0.50 is about 72.41 meV and 77.39 meV, respectively. The Raman spectra of Fe3−xMnxO4 at room temperature reveal five phonons modes for Fe3−xMnxO4 (0.01 ≤ x ≤ 0.50) as expected for the magnetite (Fe3O4). Increased Mn2+ doping at Fe site leads to a gradual changes in phonon modes. The Raman active mode for Fe3−xMnxO4 (x = 0.50) at ≅641.5 cm−1 is shifted as compared to parent Fe3O4 at ≅669.7 cm−1, inferring that Mn+2 ions are located mostly on the octahedral sites. The laser power is fixed to 5 mW causes the bands to broaden and to undergo a small shift to lower wave numbers as well as increase in the full width half maxima for A1g phonon mode with the enhancement of Mn2+ doping. Mössbauer spectroscopy probes the site preference of the substitutions and their effect on the hyperfine magnetic fields confirms that Mn+2 ions are located mostly on the octahedral sites of the Fe3−xMnxO4 spinel structure.

► Synthesized Fe3−xMnxO4 (0.10 ≤ x ≤ 0.50) possesses cubic inverse spinel structure.
► Resistivity data shows Verwey transition for Fe3O4 (Fe2.99Mn0.01O4) at 123 (117) K.
► SPC model explains the resistive behavior of Fe2.9Mn0.1O4 and Fe2.5Mn0.5O4 samples.
► Mn2+doped Fe3O4 reveals five Raman active modes for cubic spinel structure.
► Mössbauer spectrum shows Fe is +3 oxidation states and Mn2+ entered into B sites.