Surface spin asymmetry of O 2p and Ba 5p states in BaTiO3(001)

Abstract

Spin asymmetry is detected in both O 2p and Ba 5p valence states of a 12.5 nm thick (001) ferroelectric barium titanate single crystal thin film, BaO terminated, with outwards polarization. Although the occurrence of spin asymmetry in O 2p states is understandable and may be related to the surface charging of the outer layer, which induces a spin imbalance of surface oxygens, the observed spin asymmetry in deeper Ba 5p states, while still having electrons occupying states of lower binding energy, is less intuitive. This phenomenon may be explained by taking into account chemical shifts and crystal field effects together in the presence of surface charges on the surface BaO layer. In the roughest approximation, any additional positive charge is distributed equally on surface Ba and O atoms. The overall surface charge density is quite similar to the estimated value of the polarization.