The ${\text{NiO}}_4$ plaquettes in ${\text{La}}_2{\text{NiO}}_{4.17}$, a cousin of the hole-doped high-temperature superconductor ${\text{La}}_{2-x}{\text{Sr}}_x{\text{CuO}}_4$, have been studied by ${}^{61}\text{N}\text{i}$ NMR in 14 T in a single crystal enriched in ${}^{61}\text{N}\text{i}$. Doped and undoped plaquettes are discriminated by the shift of the NMR resonance, leading to a small line splitting, which hardly depends on temperature or susceptibility. The smallness of the effect is additional evidence for the location of the holes as deduced by Schüßler-Langenheine et al. [Phys. Rev. Lett. 95, 156402 (2005)]. The increase in linewidth with decreasing temperature shows a local-field redistribution, consistent with the formation of charge-density waves or stripes. For comparison, we studied, in particular, the grandmother of all planar antiferromagnets ${\text{K}}_2{\text{NiF}}_4$ in the paramagnetic state using natural abundant ${}^{61}\text{N}\text{i}$. The hyperfine fields in both two-dimensional compounds appear to be remarkably small, which is well explained by super(transferred) hyperfine interaction. In ${\text{K}}_2{\text{NiF}}_4$, the temperature dependence of the susceptibility and the Knight shift cannot be brought onto a simple scaling curve. This unique feature is ascribed to a different sensitivity for correlations of these two parameters.

• Received 16 September 2009

DOI:https://doi.org/10.1103/PhysRevB.81.094419