Effect of Mn doping on structural, dielectric and magnetic properties of BiFeO₃ thin films

Bismuth iron oxide is amongst the class of materials that exhibit simultaneous presence of ferromagnetic and ferroelectric properties with potential applications in spintronic devices. However, there are some problems associated with BiFeO₃ including large leakage current, volatile nature of Bi₂O₃ along with weak ferromagnetic/antiferromagnetic behavior. In order to overcome these difficulties we here report the effect of manganese (Mn) doping on BiFeO₃ (BiFe_1−xMn_xO₃ where x = 0.0–0.3, with interval of 0.05) thin films prepared using sol–gel and spin coating method. X-ray diffractometer (XRD) results show formation of phase pure rhombohedrally distorted perovskite structure. However, with the increase in Mn content, XRD peak positions shift to higher angle indicating reduction in lattice parameters and consequently the unit cell volume. Crystallite size in un-doped and Mn-doped BiFeO₃ films is below cycloidal spin arrangement of BiFeO₃, i.e. 62 nm. This along with charge compensation mechanism, arising due to replacement of trivalent cation with divalent ion, enhances the magnetic properties of BiFe_1−xMn_xO₃ thin films. Ferromagnetic behavior instead of antiferromagnetic nature of BiFeO₃ is observed in these BiFe_1−xMn_xO₃ thin films for all Mn concentrations. High saturation magnetization of 102 emu/cm³ was observed for Mn content of 0.2. Dielectric constant increases and the dielectric loss decreases as the dopant concentration is increased resulting in high dielectric constant and low dielectric loss at x = 0.25. The surface work function (wf) has been calculated using Scanning Kelvin Probe technique. The wf results are correlated to the structural and then dielectric properties.