Structural evolution from Bi_(4.2)K_(0.8)Fe2O_(9+δ) nanobelts to BiFeO3 nanochains in vacuum and their multiferroic properties

摘要

In this paper, we report the structural evolution of Bi_(4.2)K_(0.8)Fe2O_(9+δ) nanobelts to BiFeO3 nanochains and the related variations in multiferroic properties. By using in situ transmission electron microscopy with comprehensive characterization, it was found that the layered perovskite multiferroic Bi_(4.2)K_(0.8)Fe2O_(9+δ) nanobelts were very unstable in a vacuum environment, with Bi being easily removed. Based on this finding, a simple vacuum annealing method was designed which successfully transformed the Bi_(4.2)K_(0.8)Fe2O_(9+δ) nanobelts into one-dimensional BiFeO3 nanochains. Both the Bi_(4.2)K_(0.8)Fe2O_(9+δ) nanobelts and the BiFeO3 nanochains showed multiferroic behavior, with their ferroelectric and ferromagnetic properties clearly established by piezoresponse and magnetic measurements, respectively. Interestingly, the BiFeO3 nanochains had a larger magnetization than the Bi_(4.2)K_(0.8)Fe2O_(9+δ) nanobelts. Moreover, the BiFeO3 nanochains exhibited a surprisingly large exchange bias with small training effects. This one-dimensional BiFeO3 multiferroic nanostructure characterized by a relatively stable exchange bias offers important functionalities that may be attractive for device applications.