Abstract: Clarifying how spinel inversion affects the magnetic coupling nature at antiphase boundaries (APBs) is crucial for understanding the intriguing magnetic behaviors of spinel ferrites. Here, MgFe₂O₄ films with an inversion coefficient of 2/3 are grown on MgO substrates using pulsed laser deposition (PLD). Investigations by state-of-the-art transmission electron microscopy suggest that two types of APBs are formed on the MgFe₂O₄ {110} crystal planes. The type I and type II APBs have the crystal translation of $(1 / 4) a[110]+(1 / 6) a[1 \overline{1} 2]$ and $(1 / 4) a[110]$ at the boundary, respectively. First-principles calculations reveal that both type I and type II APBs tend to form antiferromagnetic coupling when the inversion coefficient in MgFe₂O₄ is zero. When the inversion coefficient rises to 2/3 due to the occupation of Mg²⁺ cations in octahedral sites, the magnetic coupling at the type I APBs changes to the ferromagnetic coupling, while the type II APBs still remain the antiferromagnetic one. The magnetic coupling modes of the APBs are closely related to the Fe-O-Fe superexchange interaction across the boundaries. Our findings clarify the atomistic mechanism of how spinel inversion affects the magnetic properties of spinel ferrites, which will promote the applications of magnetoelectricity materials with partial inversion.

Key words: MgFe₂ O₄, Antiphase boundary, Cation distribution, Magnetic coupling, Transmission electron microscopy, First-principles calculations