Spin Stripe Order in a Square Planar Trilayer Nickelate

Trilayer nickelates, which exhibit a high degree of orbital polarization combined with an electron count ($d^{8.67}$) corresponding to overdoped cuprates, have been identified as a promising candidate platform for achieving high-$T_c$ superconductivity. One such material, ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$, undergoes a semiconductor-insulator transition at $\sim 105\mathrm{K}$, which was recently shown to arise from the formation of charge stripes. However, an outstanding issue has been the origin of an anomaly in the magnetic susceptibility at the transition and whether it signifies the formation of spin stripes akin to single layer nickelates. Here we report single crystal neutron diffraction measurements (both polarized and unpolarized) that establish that the ground state is indeed magnetic. The ordering is modeled as antiferromagnetic spin stripes that are commensurate with the charge stripes, the magnetic ordering occurring in individual trilayers that are essentially uncorrelated along the crystallographic $c$ axis. A comparison of the charge and spin stripe order parameters reveals that, in contrast to single-layer nickelates such as ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_4$ as well as related quasi-2D oxides including manganites, cobaltates, and cuprates, these orders uniquely appear simultaneously, thus demonstrating a stronger coupling between spin and charge than in these related low-dimensional correlated oxides.

Figure 1

(a) Unpolarized neutron scattering intensity in the ($hk0$) plane measured for ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$ at $T=1.8\mathrm{K}$ with 120 K data subtracted. (b) Scan along ($4/3,0,l$) at $T=2.0\mathrm{K}$ with 120 K data subtracted. Uncertainties represent one standard deviation, derived from the square roots of the numbers of counts. The simulated intensities in the ($hk0$) plane as well as along ($4/3,0,l$) for the uncorrelated trilayer model described in the text and shown in Fig. 3 are shown in (c) and (d), respectively.

Figure 2

Spin polarized neutron diffraction from ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$ as measured on MACS in the ($h0l$) plane with neutron spin polarization perpendicular to the plane. (a) Scans along ($h$, 0, 0) through ($4/3$,0,4) in the spin-flip channel at 1.5 (blue) and 120 K (red). (b) The same scans in the non-spin-flip channel. Uncertainties represent one standard deviation, derived from the square roots of the number of counts. Data have been corrected for polarization efficiency.

Figure 3

(a) Uncorrelated trilayer model for the spin ordering, displayed layer by layer. ${\mathrm{Ni}}^{1+}$ sites are shown in blue, and nonmagnetic ${\mathrm{Ni}}^{2+}$ sites are shown in red. Moments pointing into the plot are shown by $\otimes$, while moments pointing out of the plot are shown as $\odot$. The intra-trilayer coupling as well as the coupling across stripes is labeled. (b) Three-dimensional perspective of the structure shown in (a).

Figure 4

Temperature dependence of the charge superlattice peak ($13/3$, 3, 0) measured with x rays (a), spin superlattice peak ($4/3$, 0, 4) measured with neutrons (b), magnetic susceptibility (c), and first derivative of the magnetic susceptibility (d). Uncertainties in (b) represent one standard deviation, derived from the square root of the number of counts. The fit in (b) corresponds to a power law as described in the text.