Improved magnetic and piezoresponse behavior of cobalt substituted BiFeO3 thin film

Piezoresponse force microscopy (PFM) technique has been utilized to characterize the nanoscale electromechanical properties of chemical solution deposited pristine (BiFeO3, BFO) and 5% Cobalt-substituted bismuth ferrite (BiFe0.95Co0.05O3, BFCO) thin films. Distinct PFM contrast was observed on the films' surface both in out-of-plane and in-plane modes. Piezoresponse signal was larger in BFCO film than BFO and the former film also exhibited negative self polarization. The calculated self polarization factor was − 0.94. Lateral signal (in-plane) changed its sign upon 180° sample rotation which ruled out spurious electrostatic contribution and confirmed piezoelectric nature of the effect. Square patterns were written by local poling and reversible nature of the piezoresponse behavior was established. Well saturated piezoelectric hysteresis loops were acquired with improved piezoelectric coefficient value in case of Co-substituted BFO film. The effect has been described on the basis of polarization rotation with doping. Magnetization of BFO film also increases with Co-substitution. The enhancement in magnetic and ferro/piezoelectric properties should be useful for multiferroic applications.

► Distinct piezoresponse contrasts were observed on BiFeO3 and BiFe0.95Co0.05O3 films.
► Larger piezoresponse signal in BiFe0.95Co0.05O3 film.
► Square patterns were written by local poling that confirmed the ferroelectric nature.
► Saturated loop and improved piezoelectric coefficient in BiFe0.95Co0.05O3 film.
► Magnetization of BiFeO3 film was also increased with Co-substitution.