Neutron Diffraction Investigations of BiFeO$_3$ Films

The study of the magnetic structure of bulk BiFeO$_3$ started with powders and evolved to single crystals when large ones became available. Single crystal studies definitively showed that the magnetic structure in the bulk was a long wavelength ``cycloid'' [4]. However, there have not been similarly detailed studies of the magnetic structure in thin films. Thus, to investigate how the thin film geometry affects the multiferroicity of BiFeO$_3$, we pursued a study of the magnetic structure of BiFeO$_3$ films as a function of film thickness and substrate orientation. BiFeO$_3$ thin films with thicknesses up to 1 micron were epitaxially grown on (100), (110), and (001) oriented SrTiO$_3$ substrates by PLD. We used D10 at the ILL to measure the 1 micron thick BiFeO$_3$ film for magnetic structure determination. Polarized and unpolarized neutron diffraction experiments were performed on BT9 and BT7 at the NCNR. We will discuss the change in the magnetic structure as a function of film thickness and orientation of the substrate.