3D oxygen vacancy order and defect-property relations in multiferroic (LuFeO${}_3$)${}_9$/(LuFe${}_2$O${}_4$)${}_1$ superlattices

Abstract

Oxide heterostructures exhibit a vast variety of unique physical properties. Examples are unconventional superconductivity in layered nickelates and topological polar order in (PbTiO${}_3$)${}_n$/(SrTiO${}_3$)${}_n$ superlattices. Although it is clear that variations in oxygen content are crucial for the electronic correlation phenomena in oxides, it remains a major challenge to quantify their impact. Here, we measure the chemical composition in multiferroic (LuFeO${}_3$)${}_9$/(LuFe${}_2$O${}_4$)${}_1$ superlattices, revealing a one-to-one correlation between the distribution of oxygen vacancies and the electric and magnetic properties. Using atom probe tomography, we observe oxygen vacancies arranging in a layered three-dimensional structure with a local density on the order of 10${}^{14}$ cm${}^{-2}$, congruent with the formula-unit-thick ferrimagnetic LuFe${}_2$O${}_4$ layers. The vacancy order is promoted by the locally reduced formation energy and plays a key role in stabilizing the ferroelectric domains and ferrimagnetism in the LuFeO${}_3$ and LuFe${}_2$O${}_4$ layers, respectively. The results demonstrate the importance of oxygen vacancies for the room-temperature multiferroicity in this system and establish an approach for quantifying the oxygen defects with atomic-scale precision in 3D, giving new opportunities for deterministic defect-enabled property control in oxide heterostructures.