Room-Temperature Multiferroics and Thermal Conductivity of 0.85BiFe_1–2xTi_xMg_xO₃–0.15CaTiO₃ Epitaxial Thin Films (x = 0.1 and 0.2)

Thin films of 0.85BiFe 1–2 x Ti x Mg x O 3 –0.15CaTiO 3 ( x = 0.1 and 0.2, abbreviated to C-1 and C-2, respectively) have been fabricated on (001) SrTiO 3 substrate with and without a conductive La 0.7 Sr 0.3 MnO 3 buffer layer. The X-ray θ–2θ and ϕ scans, atomic force microscopy, and cross-sectional transmission electron microscopy confirm the (001) epitaxial nature of the thin films with very high growth quality. Both the C-1 and C-2 thin films show well-shaped magnetization–magnetic field hysteresis at room temperature, with enhanced switchable magnetization values of 145.3 and 42.5 emu/cm 3, respectively. The polarization–electric loops and piezoresponse force microscopy measurements confirm the room-temperature ferroelectric nature of both films. However, the C-1 films illustrate a relatively weak ferroelectric behavior and the poled states are easy to relax, whereas the C-2 films show a relatively better ferroelectric behavior with stable poled states. More interestingly, the room-temperature thermal conductivity of C-1 and C-2 films are measured to be 1.10 and 0.77 W/(m·K), respectively. These self-consistent multiferroic properties and thermal conductivities are discussed by considering the composition-dependent content and migration of Fe-induced electrons and/or charged point defects. This study not only provides multifunctional materials with excellent room-temperature magnetic, ferroelectric, and thermal conductivity properties but may also stimulate further work to develop BiFeO 3 -based materials with unusual multifunctional properties.