Clean Flipping of the Electric Dipole Moment in Pd-doped BiFeO3 Film Along [111] Direction

Multiferroic materials involve multiple couplings between electricity and magnetism, especially for magnetoelectric multiferroic materials. This shows inherent coupling between magnetic and ferromagnetic materials that could be used as a mechanism to switch magnetic moment of an adjacent magnetic layer by applying an external electric field and vice-versa. The pseudocubic structure of BiFeO3, which is a multiferroic layer on a SrTiO3 (100) substrate, provides eight degenerate electric polarization directions. In addition, the leakage problem at domain walls causes great difficulty in control and application. This research aims to solve these problems by growing Pd-doped BiFeO3 and SrRuO₃ bilayers along [111] direction on atomically flat SrTiO₃ (111) substrates. The Pb doping will stop the electric leakage and the [111] orientation will simplify the polarization orientation switch states. By using a Piezoresponse Force Microscopy (PFM), we observed a very clean switch of electric polarization along [111] direction with no response on the in-plane direction to the swiped electric field. A charge accumulation phenomenon is observed that shifts the hysteresis loop similar to the exchange bias effect.