Fig. 2

a Schematic of four different structural variants and eight domain variants in (001) rhombohedral BFO film. b IP-PFM image of the BFO thin film with 71° domain wall. c Possible domain patterns for BFO film with 71° domain wall. The projected polarizations of the \(P_1^ -\), \(P_2^ -\), \(P_3^ -\), and \(P_4^ -\) are shown by the sense of arrows. d–f Polar plots of measured s-polarized SHG intensity as a function of polarization angle φ with θ = 0°, 90°, and 180°, respectively. g Contour pattern of monitored s-polarized SHG intensity vs. sample rotation angle θ and polarization angle φ. h The s-polarized SHG intensity as a function of angle θ under the fixed p_in and s_in incident light fields. i Fractions of domain variants in the BFO thin film with 71° domain wall. The symbols present the experimental data, and the lines indicate the theoretical fits. Comparison of the polarization-dependent SHG patterns with θ = 0° and 90° are as insets in d, where the green is the SHG pattern at θ = 90°. The schematic illustrations of the domain variants at angle θ = 0°, 90°, and 180° relative to incident beam are as insets