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

Co-doped BisFeTi3O15 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 （Mr） first increases and reaches the maximum value of 0.42 emu/cm^3 at x = 0.12 due to the possible Fe^3＋-O Co^3＋ ferromagnetic coupling. When x = 0.25, the Mr increases again because of the dominant Fe^3＋-O Co^3＋ ferromagnetic coupling. The remanent polarization （2Pr） of BFCT-0.25 was measured to be as high as 62 μC/cm2, a 75% increase when compared with the non-doped BFCT-0 films. The 2Pr remains almost unchanged after being subjected to 5.2 × 10^9 read/write cycles. Greatly enhanced ferroelectric properties are considered to be associated with decreased leakage current density.