Magnetic correlations in infinite-layer nickelates: An experimental and theoretical multimethod study

We report a comprehensive study of magnetic correlations in ${\mathrm{LaNiO}}_2$, a parent compound of the recently discovered family of infinite-layer (IL) nickelate superconductors, using multiple experimental and theoretical methods. Our specific heat, muon-spin rotation ($\mu \mathrm{SR}$), and magnetic susceptibility measurements on polycrystalline ${\mathrm{LaNiO}}_2$ show that long-range magnetic order remains absent down to 2 K. Nevertheless, we detect residual entropy in the low-temperature specific heat, which is compatible with a model fit that includes paramagnon excitations. The $\mu \mathrm{SR}$ and low-field static and dynamic magnetic susceptibility measurements indicate the presence of short-range magnetic correlations and glassy spin dynamics, which we attribute to local oxygen nonstoichiometry in the average infinite-layer crystal structure. This glassy behavior can be suppressed in strong external fields, allowing us to extract the intrinsic paramagnetic susceptibility. Remarkably, we find that the intrinsic susceptibility shows non-Curie-Weiss behavior at high temperatures, in analogy to doped cuprates that possess robust nonlocal spin fluctuations. The distinct temperature dependence of the intrinsic susceptibility of ${\mathrm{LaNiO}}_2$ can be theoretically understood by a multimethod study of the single-band Hubbard model in which we apply complementary cutting-edge quantum many-body techniques (dynamical mean-field theory, cellular dynamical mean-field theory, and the dynamical vertex approximation) to investigate the influence of both short- and long-ranged correlations. Our results suggest a profound analogy between the magnetic correlations in parent (undoped) IL nickelates and doped cuprates.

Figure 1

(a) Specific heat $C_p$ of polycrystalline ${\mathrm{LaNiO}}_2$ (red) and ${\mathrm{LaNiO}}_3$ (blue). (b) $C_p/T$ as a function of $T^2$. Solid lines are standard model (SM) fits of ${\mathrm{LaNiO}}_2$ and ${\mathrm{LaNiO}}_3$ between $T=6$ and 25 K according to $C_p=\gamma T+\beta T^3$ (see text). The inset shows $C_p/T$ as a function of $1/T^2$. The black arrow centered at $T=6$ K indicates the onset of a deviation from the extrapolated SM fit (solid red line) for ${\mathrm{LaNiO}}_2$. The dashed black line is a model fit of ${\mathrm{LaNiO}}_2$ between $T=2$ and 6 K according to $C_p=\gamma T+\beta T^3+\alpha T^{3}ln\left(T\right)$, which accounts for an extra contribution due to paramagnon excitations (PE).

Figure 2

(a) Zero-field (ZF) $\mu \mathrm{SR}$ spectra of ${\mathrm{LaNiO}}_2$ at representative temperatures. Solid lines are fits of the polarization $P\left(t\right)$ (see text). (b) Temperature dependence of the parameter $\nu$, which is indicative of the internal magnetic field. (c) Temperature dependence of the parameters ${\lambda }_{\text{L}}$, ${\lambda }_{\text{T}}$, and ${\lambda }_{\text{Dyn}}$, extracted from fits to regimes below 75 K and above 100 K, respectively. The inset shows the evolution of the parameter $\beta$ for temperatures above 100 K obtained from a simple stretched exponential fit.

Figure 3

Magnetic susceptibility of ${\mathrm{LaNiO}}_2$ in small external fields. (a) Static susceptibility $\chi$ measured upon heating after zero-field cooling (ZFC, solid line) and field-cooling (FC, dashed line), respectively, in an external field of ${\mu }_{0}H=0.1$ T. The inset shows the evolution of $\chi$ (ZFC, ${\mu }_{0}H=0.01$ T) as a function of time for an intermittent stop at $T=15$ K. (b) Real part of the dynamic susceptibility ${\chi }^{\prime }$ for different ac drive frequencies $f$. The static external field is zero and the maximum field amplitude of the ac field is $4\times {10}^{-4}$ T. Vertical dashed lines indicate the positions of the maximum for $f=99$ Hz. The inset shows the relation between the temperature $T$ of the maximum of ${\chi }^{\prime }$ and the time period $\tau ={\left(2\pi f\right)}^{-1}$ of the ac field. The solid gray, red, and blue lines are fits with an Arrhenius (Arrh.), a Vogel-Fulcher (VF), and a critical dynamical scaling (crit.) law, respectively. (c) Imaginary part of the dynamic susceptibility ${\chi }^{″}$.

Figure 4

Magnetic susceptibility of ${\mathrm{LaNiO}}_2$ in strong external fields. (a) ZFC and FC susceptibility $\chi$ in an external field ${\mu }_{0}H=7$ T. The inset shows the evolution of $\chi$ (ZFC) as a function of time for an intermittent stop at $T=2$ K. (b) Isothermal magnetization between 0 and 7 T at representative temperatures. (c) Saturation magnetization $M_{\text{sat}}$ extracted from linear fits of the isothermal magnetization curves between 5 and 7 T for temperatures between 2 and 305 K (see Appendix pp3). The inset shows $M_{\text{sat}}$ extracted from isotherms measured at higher temperatures.

Figure 5

Corrected paramagnetic susceptibility ${\chi }_{\text{corr}}$ extracted from isothermal magnetization curves by the Honda-Owen method (see Appendix pp3).

Figure 6

(a) dc susceptibility ${\chi }_{\text{theory}}$ and (b) its inverse calculated for a two-dimensional single-band Hubbard model of ${\mathrm{LaNiO}}_2$ by various many-body techniques. CDMFT (filled orange circles) and $\mathrm{D}\mathrm{\Gamma }\mathrm{A}$ (filled red squares) exhibit a deviation from Curie-Weiss behavior at low $T$ when significant nonlocal correlations set in [the dotted black line in (b) shows a respective Curie-Weiss fit from the high-$T$ regime of all three techniques]. This regime is already signaled in DMFT as an (antiferromagnetically) ordered phase for $T<T_{\text{Néel}}^{\text{DMFT}}$ (blue shaded region). For comparison to finite-size systems also the atomic values (solid green line, Curie law) and the ones of an isolated $2\times 2$ cluster (open green circles) are shown.

Figure 7

Powder x-ray diffraction pattern of ${\mathrm{LaNiO}}_3$ (a) and ${\mathrm{LaNiO}}_2$ (b) at $T=300$ K measured with $\mathrm{Cu}{K}_{\alpha }$ radiation. Solid black lines correspond to the calculated intensities from the Rietveld refinements. The calculated Bragg peak positions are indicated by vertical bars and the differences between the experimental and calculated intensities are shown as solid gray lines at the bottom.

Figure 8

Energy dispersive x-ray spectra (EDS) of a pellet of ${\mathrm{LaNiO}}_2$. The red line corresponds to an area scan, while the blue line is from a local point. The insets show the EDS maps of different elements, with Ni in green, La in magenta, and O in blue. No sudden jumps in Ni compared to La were observed.

Figure 9

ZF $\mu \mathrm{SR}$ spectra measured at various temperatures. Solid lines are fits to the data (see text).

Figure 10

$\mu \mathrm{SR}$ spectra at 290 K in different longitudinal fields (LF). Solid black lines are dynamical fits (see text).

Figure 11

(a) Static (dc) magnetic susceptibility $\chi$ of ${\mathrm{LaNiO}}_2$ in different external magnetic fields measured upon heating after zero-field cooling (ZFC, solid lines) and field cooling (FC, dashed lines), respectively. The arrows indicate the positions of the cusps in the ZFC curves. (b) Isothermal magnetic hysteresis loops of ${\mathrm{LaNiO}}_2$ measured up to ${\mu }_{0}H=0.75$ T at different temperatures. Black arrows indicate the directions of the field sweep.

Figure 12

Isothermal magnetization of ${\mathrm{LaNiO}}_2$ measured between 5 and 7 T at 2, 4, 6, 8, 10, 15, 20, 35, 50, 65, 80, 95, 110, 125, 140, 155, 170, 185, 200, 215, 230, 245, 260, 275, 290, and 305 K, respectively (filled symbols from dark blue to light blue). The data ($M/H$) are plotted as a function of $1/H$, according to the Honda-Owen method. Solid lines (from dark to light gray) are linear fits for each temperature. The $y$-intercept of each linear fit corresponds to the corrected paramagnetic susceptibility ${\chi }_{\text{corr}}$ displayed in Fig. 5 in the main text.

Figure 13

Corrected paramagnetic susceptibility ${\chi }_{\text{corr}}$ of ${\mathrm{LaNiO}}_2$ across a wide temperature range. Red data points are reproduced from Fig. 5 in the main text. Dark gray data points were extracted from isotherms (Fig. 14) measured in a high-temperature setup (see Methods).

Figure 14

Isothermal magnetization measured between 5 and 7 T at 300, 500, 600, 650, and 700 K, respectively (filled symbols from dark blue to light blue). Solid lines (from dark to light gray) are linear fits for each temperature to extract ${\chi }_{\text{corr}}$ (see Fig. 13). The data ($M/H$) are plotted as a function of $1/{\mu }_{0}H$, according to the Honda-Owen method.