Magnetic and Electronic Properties in Ruddlesden–Popper Lanthanum Nickelates from First-Principles Calculations

The bilayer Ruddlesden–Popper (RP) nickelate La₃Ni₂O₇ has been reported to exhibit a high superconducting transition temperature of approximately 80 K under pressure. Furthermore, different kinds of RP nickelates with long-range structural order have been synthesized. Here, by performing first-principles calculations, we systematically investigate the magnetic and electronic properties of RP lanthanum nickelates, including La₂NiO₄ (stacked with a monolayer of NiO₆ blocks, LNO-11), La₂NiO₄·La₃Ni₂O₇ (stacked with a monolayer and a bilayer of NiO₆ blocks, LNO-12), La₃Ni₂O₇ (stacked with a monolayer and a trilayer of NiO₆ blocks, LNO-13) and bilayer La₃Ni₂O₇ (stacked with a bilayer of NiO₆ blocks, LNO-22). Our results show that the magnetic coupling and electronic structure in the constituent layers of the RP structure are dependent on the thickness of the constituent layers. The magnetic coupling in the constituent layers displays an antiferromagnetic (AFM) to ferromagnetic (FM) transition with the increase of the thickness of the constituent layers. The constituent monolayer in LNO-11, LNO-12, and LNO-13 shows an AFM order. The constituent bilayer with charge ordering of Ni²⁺ and Ni³⁺ in LNO-12 and LNO-22 displays a stripe order. The constituent trilayer in LNO-13 exhibits a ferromagnetic coupling. Furthermore, the electronic structures of RP nickelate show an insulator–metal transition with the increase of the thickness of the constituent bilayer. LNO-11, LNO-12, and LNO-22 with charge ordering of Ni²⁺ and Ni³⁺ are insulating, while LNO-22 without charge ordering and LNO-13 become metallic. Our work potentially provides insight into the mechanism of superconductivity and a theoretical reference for studying mixed-stacked nickelate superconductors.