Oxygen vacancies at antiphase boundaries in cation-disordered spinel ferrite

Antiphase boundaries (APBs) are intrinsic defects in Fe₃O₄ films that significantly alter their magnetic and transport properties compared to the bulk material due to antiferromagnetic interactions across these boundaries. In the study, we realize ferromagnetically coupled APBs in spinel ferrite by cation disorder and oxygen vacancy defects. Ni and Zn are introduced into Fe₃O₄ to form Ni and NiZn ferrites and cation disorder is found in the two ferrites with Ni and Zn occupied in both octahedral and tetrahedral sites. This disorder transforms the ferrites from semiconductors into half-metals, characterized by a nonzero majority spin density of states (DOS) and a zero minority spin DOS at Fermi level. The stacking fault of the cations (Fe, Ni, Zn) at the APB induces excess negative charges, leading to the formation of oxygen vacancies as charge compensators. These vacancies disrupt the antiferromagnetic superexchange interactions, preventing spin polarization reversal across the APB, thereby enabling ferromagnetic coupling. This work provides insights into tuning the magnetic properties of APBs in spinel ferrites through defect engineering and cation manipulation.