Local metallic and structural properties of the strongly correlated metal $\mathrm{LaNiO}{}_3$ using ${}^8\mathrm{Li}$ $\beta \text{–}\mathrm{NMR}$

We report $\beta$-detected NMR of ion-implanted ${}^8\mathrm{Li}$ in a single crystal and thin film of the strongly correlated metal ${\mathrm{LaNiO}}_3$. Spin-lattice relaxation measurements reveal two distinct local environments, both metallic as evident from $T$-linear Korringa $1/T_1$ below $200\mathrm{K}$ with slopes comparable to other metals. A small approximately temperature-independent Knight shift of $\sim 74\mathrm{ppm}$ is observed, yielding a normalized Korringa product characteristic of substantial antiferromagnetic correlations. We find no evidence for a magnetic transition from 4 to $310\mathrm{K}$. The similarity of these features in the two very different samples indicates that they are intrinsic and unrelated to dilute oxygen vacancies. We attribute the two environments to two distinct but similar crystallographic ${}^8\mathrm{Li}$ sites and not to any form of phase inhomogeneity, but this is inconsistent with the conventional rhombohedral structure of ${\mathrm{LaNiO}}_3$, and also cannot be simply explained by the common alternative orthorhombic or monoclinic distortions.

Figure 1

Examples of SLR data for ${}^8\mathrm{Li}^{+}$ in ${\mathrm{LaNiO}}_3$ with $B_0=6.55\mathrm{T}$ with fits (lines) using the triexponential of Eq. (1) convoluted with the $4\mathrm{s}$ beam pulse indicated by the shaded area. The data are normalized by their apparent $t=0$ asymmetry; see Appendix pp2.

Figure 2

The slow (a) and fast (b) SLR rates as a function of temperature for ${}^8\mathrm{Li}$ in the ${\mathrm{LaNiO}}_3$ crystal (red circles) and $38\mathrm{nm}$ film (blue squares). Both rates exhibit a linear Korringa behavior below $200\mathrm{K}$ that agrees quantitatively between the two samples. The thick gray lines are the best-fit slopes, with the values shown. The shading shows the region bounded by a $1\sigma$ change to the slope. The vertical shaded region marks the onset of the high-temperature decrease in the single-crystal ${\chi }_0\left(T\right)$ [15] (see text).

Figure 3

Temperature dependence of the ${}^8\mathrm{Li}$ resonance in the ${\mathrm{LaNiO}}_3$ crystal at $6.55\mathrm{T}$. At low temperature, the resonance is broadest and weakest, with the amplitude growing monotonically and the width narrowing by a factor of $\sim 2$ as the temperature is raised. A small, nearly temperature-independent positive shift relative to MgO is evident. The spectra are normalized by the off-resonance baseline asymmetry and offset to clearly display the temperature dependence. The ${}^8\mathrm{Li}$ resonance in the LNO film at $300\mathrm{K}$ is also shown (open squares); it is remarkably similar to the crystal both in shift $K$ and width.

Figure 4

Temperature dependence of the ${}^8\mathrm{Li}^{+}$ resonance in the ${\mathrm{LaNiO}}_3$ crystal: (a) Knight shift $\mathcal{K}$, (b) full width at half maximum (FWHM), and (c) amplitude. The amplitude is normalized by the off-resonance baseline asymmetry. In (a), the solid gray curve and right scale show the magnetic susceptibility of the crystal [15]. Horizontal lines show estimates of the Knight shift for the slow (blue) and fast (green) relaxing components at $300\mathrm{K}$. The vertical arrows emphasize that the values are lower limits (see text). The black solid curves in panels (b) and (c) are guides. The values for the $38\mathrm{nm}$ film at $300\mathrm{K}$ are also shown (open squares).

Figure 5

Schematic of the interstitial ${}^8\mathrm{Li}^{+}$ site $P$ in perovskite oxides. For simplicity, the illustrated structure is cubic; however, the site retains the same coordination when the symmetry is lowered. (a) Side view illustrating that the Li site is halfway between two neighboring La. (b) Top view of the ${\mathrm{NiO}}_2$ plane showing that the Li site is coordinated with 4 oxygen anions.

Figure 6

Stopping distribution of ${}^8\mathrm{Li}$ in a ${\mathrm{LaNiO}}_3$ crystal (top), and a $38\mathrm{nm}$ film deposited on LSAT (bottom). Obtained using SRIM [48] calculations for implantation energies $E$ of $27.9\mathrm{keV}$ and $2.9\mathrm{keV}$. Each simulation used ${10}^5$ Li ions.

Figure 7

An example decomposition of the SLR fit to Eq. (1) for the crystal at $300\mathrm{K}$ and $6.55\mathrm{T}$, showing the individual components: Background (green), fast (red), and slow (blue). Also shown: The sum of slow and fast (purple) and the total fit (gray).

Figure 8

Comparison of the raw and (demagnetization) corrected shift of the ${}^8\mathrm{Li}$ NMR in the ${\mathrm{LaNiO}}_3$ crystal. The raw shift is obtained by using Eq. (2), while the corrected shift is obtained by applying the demagnetization correction in Eq. (C1). The results at $300\mathrm{K}$ for the film are shown as open squares. Overlaid on the corrected shifts is the molar susceptibility of the crystal [15], right scale.