Coherent Acoustic Phonons and Ultrafast Carrier Dynamics in BaTiO3-BiFeO3Films and Nanorods

BiFeO₃ has become a popular multiferroic material as an alternative to PZT since it is lead free. The addition of about 25% BaTiO₃ in solid solution has been shown to substantially improve the coupling between electric, magnetic, optical, and structural orders parameters and offers the possibility of developing high speed multifunctional devices. We performed two-color (400 nm pump, 800 nm probe) time resolved transient reflectivity measurements of (1-x) BaTiO₃ -(x) BiFeO₃, with x = 0.725 and BaTiO₃-BiFeO₃ nanorods. Our results show ultrafast carrier dynamics in BaTiO₃-BiFeO₃, which we interpret as diffusion of the photoexcited carriers away from the surface with an ambipolar diffusion constant that is below 1-2 cm²/s.The differential reflectivity also showed evidence of coherent acoustic phonons (CP) in both the films and nanorod samples at lower temperatures (100 K).. The ability to generate strain via ultrafast optics can offer the intriguing possibility of dynamically manipulating and controlling electric and magnetic fields.