Self-Assembly of Hollow Bismuth Ferrite Spheres from Nitrate Solutions

Using the ultrasonic spray pyrolysis method, a controllable process is realized for self-assembly of spherical BiFeO3 aggregates. Powders are obtained, which exhibit as the pronounced ferromagnetic properties (the coercive force Hc at 8.8 kOe and the residual magnetization Mp at 0.08 emu/g) characteristic of conventionally sol–gel produced BiFeO3 samples (Hc and Mp approaching zero). Various manifestations of ferromagnetism are discussed. It is found that the ultimate values of magnetic characteristics are related to destruction of the antiferromagnetic cycloid as the shells of hollow BiFeO3 spheres are formed. The aggregates thus formed may be considered as an advanced type of bismuth ferrite nanostructure with no coverage in the literature.