Enhancement of saturation magnetization in epitaxial (111) BiFeO3 films by magnetic annealing

We report the enhancement of the saturation magnetization in BiFeO₃ films achieved by magnetic annealing. The saturation magnetization of the film annealed in a magnetic field is found to be 80 emu/cc, which is an increase nearly by a factor of 10 compared to the as-grown one. From the investigation of optical second harmonic generation (SHG), we observe the presence of s_out-polarization under s_in-polarization in the film annealed in a magnetic field, which implies that the spin state is homogeneous antiferromagnetic one rather than cycloidal one. We interpret the observed large enhancement in the saturation magnetization to be due to the magnetic phase transition from cycloidal to homogenous antiferromagnetic one.