The phase multiformity and domain structure of Sr3Ir2O7

Compared with 3d-electron transition metal oxides (TMOs), 5d-electron TMOs, particularly iridates, have strong competition between spin-orbit coupling and on-site Coulomb repulsion due to their comparable energies. By using aberration-corrected transmission electron microscopy, we have studied at an atomic scale the Sr3Ir2O7 sample with a bilayered perovskite structure, which is synthesized under high pressure and high temperature. In addition, we have also investigated its magnetic and electrical properties. Our results show that the Sr3Ir2O7 possesses two kinds of structures: a tetragonal structure (I4/mmm) and an orthorhombic structure (Ccce) with complex magnetic and electrical properties. We observed that there are often 90° domain structures along the b axis of the orthorhombic structure of Sr3Ir2O7, which might be associated with the essence of antiferromagnetic 90° domains.