Multiferroic properties of sol-gel derived Bi5Fe1-xCoxTi3O15 thin films

Co-doped Bi5FeTi3O15 thin films (BFCT-x, Bi5Fe1-xCoxTi3O15) were prepared using a sol-gel technique. XRD patterns confirm their single phase Aurivillius structure, and the corresponding powder Rietveld analysis indicates the change of space group around x = 0.12. The magnetic hysteresis loops are obtained and ferromagnetism is therefore confirmed in BFCT-x thin films. The remanent magnetization (M-r) first increases and reaches the maximum value of 0.42 emu/cm(3) at x = 0.12 due to the possible Fe3+-O-Co3+ ferromagnetic coupling. When x = 0.25, the M-r increases again because of the dominant Fe3+-O-Co3+ ferromagnetic coupling. The remanent polarization (2P(r)) of BFCT-0.25 was measured to be as high as 62 mu C/cm(2), a 75% increase when compared with the non-doped BFCT-0 films. The 2P(r) remains almost unchanged after being subjected to 5.2 x 10(9) read/write cycles. Greatly enhanced ferroelectric properties are considered to be associated with decreased leakage current density.