Structural, magnetic, and electrical studies on polycrystalline transition-metal-doped BiFeO3 thin films

We have synthesized a range of transition-metal-doped BiFeO3 thin films on conducting silicon substrates using a spin-coating technique from metal-organic precursor solutions. Bismuth, iron and transition-metal-organic solutions were mixed in the appropriate ratios to produce 3% transition-metal-doped samples. X-ray diffraction studies show that the samples annealed in a nitrogen atmosphere crystallize in a rhombohedrally distorted BiFeO3 structure with no evidence for any ferromagnetic secondary phase formation. We find evidence for the disappearance of the 404 cm(-1) Raman mode for certain dopants indicative of structural distortions. The saturation magnetization of these BiFeO3 films has been found to increase on doping with transition metal ions, reaching a maximum value of 8.5 emu cm(-3) for the Cr-doped samples. However, leakage current measurements find that the resistivity of the films typically decreases with transition metal doping. We find no evidence for any systematic variation of the electric or magnetic properties of BiFeO3 depending on the transition metal dopant, suggesting that these properties are determined mainly by extrinsic effects arising from defects or grain boundaries.