Atomic origin of magnetic coupling of antiphase boundaries in magnetite thin films

Abstract

Revealing the magnetic coupling nature of boundary defects is crucial for in-depth understanding of the behavior and properties of magnetic materials and devices. Here, magnetite (i.e., Fe3O4) thin films were grown epitaxially on (100) SrTiO3 single-crystal substrates by pulsed laser deposition. Atomic-scale scanning transmission electron microscopy characterizations reveal that three types of antiphase boundaries (APBs) are formed in the Fe3O4 thin film. They are the (100) APB that is formed on the (100) plane with a crystal translation of (1/4)a[011¯], the type I and type II (110) APBs that are both formed on the (110) plane with the same crystal translation of (1/4)a[101] but different terminated atomic planes. The type I (110) APB is terminated at the atomic plane with mixed tetrahedral- and octahedral-sites Fe atoms, the type II (110) APB is terminated at the octahedral-site Fe plane. First-principles calculations reveal that the (100) APB and the type I (110) APB tend to form the ferromagnetic coupling that will not decrease the spin polarization of Fe3O4 films, while the type II (110) APB prefers to form the antiferromagnetic coupling that will degrade the magnetic properties. The magnetic coupling modes of the APBs are closely related to the Fe-O-Fe bond angles across the boundaries.