Enhanced ferromagnetism in Ni doped Aurivillius compound Bi₆Fe₂Ti₃O₁₈ thin films prepared by chemical solution deposition

Ni doped Aurivillius Bi₆Fe₂Ti₃O₁₈ (xBFNTO, x = 0, 0.3, 0.6, 0.9) thin films with greatly enhanced ferromagnetism have been successfully synthesized on fused quartz substrate using a non-toxic solution-based method. The use of earth abundant materials and convenient annealing processes imply the great potential on industrial manufacture of multiferroic information storage. It can be found that Ni ions doping not only leads to an enlarged crystal lattice but also contributes to the formation of larger and column-like grains compared with pure BFTO thin film. Besides, Raman spectroscopy makes additional remarks on the specific doping position of Ni ions. Most importantly, highly improved magnetism has been detected by M-H curves which can be resulted from the anti-DM interaction. The doping level of Ni and magnetization of xBFNTO shows non-linear relationship which is possible to be explained by multivalent Ni ions (Ni²⁺, Ni³⁺), and the optimum doped concentration has been explored at x = 0.6 (M_s at 4.806 emu/cm³⁾. This work moves a solid step on studies of layer-structured Aurivillius compounds.