Strong pinning effect and magnetic nanodomain formation by coupling between magnetic and crystallographic domains in the ordered double perovskite Ba₂FeMoO₆

We investigated relations between magnetic and crystallographic domains in a single crystal of an ordered double perovskite, Ba₂FeMoO₆, by means of transmission electron microscopy. By direct observation of the magnetic domain and antiphase domain structures, we demonstrated that magnetic domain walls perfectly coincide with crystallographic antiphase domain boundaries. In addition, we observed a change of magnetic domain structures by applying magnetic fields. Most of the magnetic domains undergo the rotation so as to be along the applying fields, while the local regions with magnetization direction opposite to the applying field remain adjacent to the antiphase boundary. This suggests a strong pinning effect on the magnetic domains at the antiphase boundaries. Moreover, we successfully observed a magnetic nanodomain structure derived from coupling between magnetic and structural ordering domains where Fe∕Mo short-range ordering was developed. We found that the magnetic domain structure in the ordered double perovskite is significantly affected by the crystallographic structures, i.e., the antiphase boundary and the short-range ordering, due to their strong mutual coupling.