Research progress of multiferroicity in Bi-layered oxide single-crystalline thin films

Abstract

Room temperature multiferroics with a single phase is very rare, and magnetic elements doped Bi-layered Aurivillius oxides are an important family of room temperature single phase multiferroics. However, due to the lack of single crystalline samples, the multiferroic related researches of these materials are mostly based on polycrystalline bulk or thin film samples. And the multiferroic characterizations are performed mostly by using the bulk type of samples. Therefore the studies of the origin and mechanism of the multiferroicity of these materials are extremely difficult. Recently, multiple magnetic elements doped singlecrystalline thin films have been successfully prepared, which makes it possible to study the physics mechanism of the Bi-layered Aurivillius oxides of multiferroicity. The current study shows that most of the single-crystalline thin films exhibit in-plane orientated spontaneous ferroelectric polarization and very weak room temperature magnetism. Moreover, at low temperatures the single-crystalline films exhibit a second magnetic transition. The resonant inelastic X-ray scattering experiments indicate that the doped structure exhibits a changed crystal field split, which may enhance the weak ferromagnetism through Dzyaloshinskii-Moriya interaction. On the other hand, the polarized neutron reflectivity experiments reveal that the single-crystalline thin film possesses much weaker room temperature magnetism than the bulk sample, which indicates that the origin of the magnetism and the magnetoelectric coupling in the single-crystalline samples are different from those in the polycrystalline samples. The current study of the multiferroicity in the single-crystalline Bi-layered Aurivillius thin film opens the road to designing better multiferroic systems of the Aurivillius materials.