NMR evidence for spin fluctuations in the bilayer nickelate La${}_3$Ni${}_2$O${}_6$

We report nuclear magnetic resonance data in the bilayer nickelate La${}_3$Ni${}_2$O${}_6$. This material belongs to a family of low valence nickel oxides with square planar coordination of the Ni ions and is isoelectronic to the high temperature superconducting cuprates. Although the three layer nickelate compound exhibits a spin-state transition accompanied by antiferromagnetic order, the bilayer material shows no phase transition. The NMR data in the bilayer La${}_3$Ni${}_2$O${}_6$ reveal the presence of antiferromagnetic spin fluctuations down to 5 K that are surprisingly similar to those present in the magnetically ordered trilayer La${}_4$Ni${}_3$O${}_8$, suggesting a similar electronic structure in the paramagnetic phase of both compounds.

Figure 1

(Left) The structure of La${}_3$Ni${}_2$O${}_6$, with Ni (cyan), oxygen (red), La(1) (green), and La(2) (yellow). (Right) X-ray diffraction pattern for the La${}_3$Ni${}_2$O${}_6$ for the random powder and the aligned sample for the orientation direction aligned parallel and perpendicular to the scattering plane. The data for the perpendicular direction have been inverted for ease of comparison.

Figure 2

NMR spectra of the ${}^{139}$La in a powder aligned of La${}_3$Ni${}_2$O${}_6$ measured at several different temperatures at 11.7 T using a repetition rate on the order of $5T_1$. The solid lines are fits to two Lorentzians as described in the text.

Figure 3

The full-width-half-maximum (a) and magnetic shift (b) of the La resonance as a function of temperature. The solid line in (a) is the magnetic susceptibility measured on a random powder at 1 T.

Figure 4

(a) ${\left(T_{1}T\right)}^{-1}$ versus temperature measured at the central peak of the La spectrum for the two-layer La${}_3$Ni${}_2$O${}_6$ ($•$) and the three layer La${}_3$Ni${}_4$O${}_8$ ($\circ$) materials. The solid (dotted) line is a fit to the two(three)-layer data. Data for the La${}_3$Ni${}_4$O${}_8$ is reproduced from Ref. 4.

Figure 5

(a) ${\left(T_{1}T\right)}^{-1}$ versus temperature as in Fig. 4 plotted on a semilog scale. The solid and dotted lines are fits as described in the text.