Magnetic excitations in Nd${}_{n+1}$Ni${}_n$O${}_{3n+1}$ Ruddlesden-Popper nickelates observed via resonant inelastic x-ray scattering

Magnetic interactions are thought to play a key role in the properties of many unconventional superconductors, including cuprates, iron pnictides, and square-planar nickelates. Superconductivity was also recently observed in the bilayer and trilayer Ruddlesden-Popper nickelates, whose electronic structure is expected to differ from that of cuprates and square-planar nickelates. Here we study how electronic structure and magnetic interactions evolve with the number of layers, $n$, in thin film Ruddlesden-Popper nickelates Nd${}_{n+1}$Ni${}_n$O${}_{3n+1}$ with $n=1,3$, and 5 using resonant inelastic x-ray scattering (RIXS). The RIXS spectra are consistent with a high-spin $\mathrm{\mid }3d^8\underset{‾}{L}⟩$ electronic configuration, resembling that of La${}_{2-x}$Sr${}_x$NiO${}_4$ and the parent perovskite, NdNiO${}_3$. The magnetic excitations soften to lower energy in the structurally self-doped, higher-$n$ films. Our observations confirm that structural tuning is an effective route for altering electronic properties, such as magnetic superexchange, in this prominent family of materials.