Neutron Diffraction Investigations of Magnetism in BiFeO3 Epitaxial Films

The recovery of a modulated magnetic structure in epitaxial BiFeO3 thin films as revealed by neutron diffraction is reported. The magnetic structure in thin films is found to strongly depend on substrate orientation. The substrate orientation causes different strain–relaxation processes resulting in different thin‐film crystal structures. The (110) oriented film with a monoclinic structural phase has a single‐domain modulated magnetic structure where the magnetic moment lies in the HHL plane. For the (111) oriented film that has a rhombohedral structure, a modulated structure superimposed on the G‐type antiferromagnetic order is found. These results indicate that slight structural modifications in the BiFeO3 thin film cause drastic changes in the magnetic structure. Multiferroics are materials which undergo both magnetic and ferroelectric ordering. Such materials are rare, and BiFeO3 is one of the only ones which has shown room temperature coupling between an applied electric field and its magnetic domain structure (in bulk single crystals). While previous work has found G‐type magnetic ordering in thin films, in contrast to the spiral magnetic structure found in single crystals, our current work shows that it is possible to recover a modulated magnetic structure in thin films. This opens the possibility of creating new devices based upon modulated magnetic structures.