Origin of local magnetic exchange interaction in infiite-layer nickelates

TL;DR

This study reveals that magnetic exchange interactions in infinite-layer nickelates are weaker than in cuprates and are significantly influenced by an interstitial s orbital, offering new insights into their magnetic properties and superconductivity.

Contribution

The paper uncovers the role of an interstitial s orbital in enhancing magnetic exchange interactions in nickelates, contrasting with cuprates where superexchange is mainly via Cu-dx2-y2.

Findings

Ni-Ni superexchange is weaker than in cuprates.

Interstitial s orbital significantly enhances magnetic interactions.

Glassy spin dynamics indicate proximity to magnetic ordering.

Abstract

Significant magnetic exchange interactions have been observed in infinite-layer nickelates RNiO2 (R = La, Pr, Nd), which exhibit unconventional superconductivity upon hole doping. Despite their structural and Fermi surface similarities to cuprates, infinite-layer nickelates possess a larger charge transfer gap, which influences their magnetic exchange interactions via oxygen. In this work, we performed 17O nuclear magnetic resonance (NMR) measurements on LaNiO2 and Sr-doped LaNiO2, revealing glassy spin dynamics originating from Ni-O planes. This indicates that infinite-layer nickelates are in proximity to magnetic ordering and that magnetic correlations play a crucial role in their physics. More importantly, our analysis of the Knight shift and hyperfine coupling of 17O nuclei revealed that the Ni-Ni superexchange interaction, mediated by the {\sigma} bond between the Ni-dx2-y2 and O-p orbitals, is one order of magnitude weaker than that in cuprates. This alone cannot account for the total magnetic exchange interaction observed in nickelates. First-principles many-body calculations indicate that an interstitial s orbital near the Fermi level, coupled with the Ni-d3z2-r2 orbital, significantly enhances the superexchange interaction. This contrasts with cuprates, where magnetic interactions are predominantly governed by Cu-dx2-y2 superexchange via oxygen. Our findings provide new insights into the distinct magnetic interactions in infinite-layer nickelates and their potential role in unconventional superconductivity.