Multiferroic properties of Aurivillius phase Bi₆Fe_2−xCo_xTi₃O₁₈ thin films prepared by a chemical solution deposition route

The magnetic and ferroelectric properties of Co-doped ${\text{Bi}}_6{\text{Fe}}_2{\text{Ti}}_3{\mathrm{O}}_{18}$ thin films ${\text{Bi}}_6{\text{Fe}}_{2-x}{\text{Co}}_x{\text{Ti}}_3{\mathrm{O}}_{18}$ (BFCTO) (0 $\le x\le$ 1) are investigated. The coexistence of room-temperature ferromagnetism and ferroelectricity is observed in BFCTO thin films. The x = 0.6 sample exhibits a higher remnant magnetization $M_r$ of 8.41 emu/cm³ and a remnant polarization $P_r$ of 17.6 $\mu {\mathrm{C}/\text{cm}}^2$ compared with other BFCTO thin films. The ferromagnetism can be ascribed to the spin canting of Fe- and Co-based sublattices via the Dzyaloshinskii-Moriya interaction [I. Dzyaloshinsky, J. Phys. Chem. Solids 4, 241 (1958); T. Moriya, Phys. Rev. 120, 91 (1960)]. The change in the remnant polarization is discussed in terms of the variation of grain size and oxygen vacancies caused by Co-doping.