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

Polycrystalline samples of Fe3-xMnxO4 (x = 0.10-0.50) were prepared by a solid-state method. XRD data showed that Mn2+ doped magnetites were single phase and had a cubic inverse spinel structure. The resistivity measurements (10 < T < 300 K) for x = 0.0 and 0.01 confirmed the first order phase transition at the Verwey transition TV = 123 K and 117 K, respectively. No first order phase transition was observed for Fe3-xMnxO4 (x = 0.10-0.50). The small polaron model was used to fit the semiconducting resistivity behaviour and the activation energy epsilon-a, for samples with x = 0.10 and 0.50 at about 72.41 meV and 77.39 meV, respectively. The Raman spectra of Fe3-xMnxO4 at room temperature revealed five phonons modes for Fe3-xMnxO4 (x = 0.01-0.50) as expected for the magnetite (Fe3O4). Increased Mn2+ doping at the Fe site led to gradual changes in phonon modes. The Raman active mode for Fe3-xMnxO4 (x = 0.50) at approximately 641.5 cm-1 was shifted when compared with parent Fe3O4 at approximately 669.7 cm-1, inferring that Mn2+ ions were located mostly on the octahedral sites. The laser power fixed at 5 mW caused the bands to broaden and undergo a small shift to lower wave numbers and increased the full width half maxima for A(1g) phonon mode with the enhancement of Mn2+ doping. Mossbauer spectroscopy probed the site preference of the substitutions and their effect on the hyperfine magnetic fields confirmed that the Mn2+ ions were located mostly on the octahedral sites of the Fe3-xMnxO4 spinel structure.