Motivated by the recent discovery of superconductivity in doped ${\mathrm{NdNiO}}_2$, we study the magnetic exchange interaction $J$ in layered $d^9$ nickelates from first principles. The mother compounds of the high-$T_{\mathrm{c}}$ cuprates belong to the charge-transfer regime in the Zaanen-Sawatzky-Allen diagram and have $J$ larger than 100 meV. While this feature makes the cuprates very different from other transition metal oxides, it is of great interest whether layered $d^9$ nickelates can also have such a large $J$. However, one complexity is that ${\mathrm{NdNiO}}_2$ is not a Mott insulator due to carrier doping from the block layer. To compare the cuprates and $d^9$ nickelates on an equal basis, we study ${\mathrm{RbCa}}_2{\mathrm{NiO}}_3$ and $A_2{\mathrm{NiO}}_2{\mathrm{Br}}_2$ ($A$ denotes a cation with a valence of $2.5+$), which were recently designed theoretically by block-layer engineering. These nickelates are free from the self-doping effect and belong to the Mott-Hubbard regime. We show that these nickelates share a common thread with the high-$T_{\mathrm{c}}$ cuprates in that they also have a significant exchange interaction $J$ as large as about 100 meV.

• Received 30 June 2020
• Revised 28 September 2020
• Accepted 29 September 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.043144

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Published by the American Physical Society