Surface ferromagnetism of complex defects lead‐free ferroelectric Bi0.5Na0.5TiO3 materials

Abstract

The complex surface defects induced magnetic properties of lead‐free ferroelectric Bi0.5Na0.5TiO3 (110) materials system are investigated by using the density‐functional theory. Various types of surface defects were considered for calculation, including antisite, vacancies and interstitial defects. The calculated results indicated that a perfect Bi0.5Na0.5TiO3 (110) surface produced zero magnetic moments. The conduction band was mostly contributed from Bi‐6p and Ti‐3d levels, where the valence band was built from O‐2p. The antisite defects where Na replaced for Bi‐site induced nonzero magnetic moments because of unsymmetrical spin O‐2p up and O‐2p down. While, the observation in nonzero magnetic moment of antisite defects Bi substitute for Na‐site were originated from Ti‐3d and Na‐2s. The Na and Bi vacancies on the surface were tuned to the ferromagnetic because of the unsymmetrical contribution of O‐2p, while the Ti and O vacancies were not. The Na and Bi surface interstitials induced the magnetic moments because of the contribution of the difference between Ti‐3d and Bi‐6p, respectively, while the Ti and O surface interstitials not induced the magnetic moments. We expected that our results could help to control chemical defects in new green multiferroic materials for smart electronic devices.