Discerning lattice and electronic structures in under- and over-doped multiferroic Aurivillius films

Aurivillius type multiferroic thin films with controllable doping have not been studied. Here, we achieve accurate doping of (La,Bi)6Fe2− x Ni x Ti3O18 epitaxial films using two-target pulsed laser deposition. An upper doping limit of x ∼ 0.4 for fabricating the single-phase structure is found. In over-doped films, secondary phases appear and the Ni valence is close to 2+. The under-doped films exhibit a single-phase and the measured electronic structure agrees with a stoichiometric phase. The multiferroic properties of the single-phase films with under-doping are probed. Our study reveals the doping limit in the Aurivillius-type multiferroic system and demonstrates the lattice-structure and electronic-structure difference between the under- and over-doped films.