Microstructure and phase control in Bi-Fe-O multiferroic nanocomposite thin films

摘要

We report on the controlled multiphase thin film growth in the Bi-Fe-O system. By varying the deposition oxygen pressure, the dominant phase formed in the film continuously changes from ferroelectric BiFeO_3 to a mixture of α-Fe_2O_3 and ferromagnetic γ-Fe_2O_3. X-ray diffraction and high-resolution transmission electron microscopy have revealed that epitaxial multiferroic nanocomposites consisting of BiFeO_3 and Fe_2O_3 are formed when the deposition pressure is ≈ 5 mTorr. In order to investigate the previously reported anomalous enhancement in magnetization in BiFeO_3, we have fabricated a thickness gradient pure BiFeO_3 film. The out-of-plane lattice constant was found to increase continuously as the thickness is decreased from 300 to 5 nm, but no significant enhancement in magnetization was observed.