Magnetism of the alternating monolayer-trilayer phase of La$_3$Ni$_2$O$_7$

Abstract

Understanding the magnetic ground state of Ruddlesden-Popper nickelates is crucial, as these materials exhibit superconductivity under high pressure and host competing electronic orders that may play a key role in the pairing mechanism. In this work, we investigate the magnetic properties of the alternating monolayer-trilayer phase of La$_3$Ni$_2$O$_7$ (1313-La$_3$Ni$_2$O$_7$) using muon-spin rotation/relaxation ($μ$SR) under both ambient and hydrostatic pressure conditions. The monolayer-trilayer phase develops incommensurate magnetic order below approximately 150 K, with a mean ordering temperature of $T_{SDW} \simeq 123$ K and a transition width of $ΔT_{SDW} \simeq 15$ K. The abrupt onset of the internal magnetic field indicates a first-order-like transition. Hydrostatic pressure ($p$) suppresses the magnetic ordering temperature at a rate of $dT_{SDW}/d p \simeq -3.9$ K/GPa, demonstrating a progressive destabilization of the ordered state. By comparison with the bilayer 2222-La$_3$Ni$_2$O$_7$ and the trilayer 3333-La$_4$Ni$_3$O$_{10}$ systems, and within a unified phenomenological framework, systematic trends are identified linking the pressure dependence of $T_{SDW}$, the (in)commensurability of the magnetic order, and the character of the magnetic transition. These trends consistently indicate a gradual reduction of electronic correlation strength from the bilayer to the monolayer-trilayer and trilayer nickelates. This hierarchy suggests that the higher superconducting transition temperature observed in the 2222 phase may be closely connected to its more strongly correlated electronic nature. These results position the alternating monolayer-trilayer 1313-La$_3$Ni$_2$O$_7$ as an intermediate member linking the magnetic behavior of the bilayer 2222-La$_3$Ni$_2$O$_7$ and the trilayer 3333-La$_4$Ni$_3$O$_{10}$ Ruddlesden-Popper compounds.

Figures (12)

• Figure 1: (a) Raman spectra from selected positions on a La$_3$Ni$_2$O$_7$ single crystal. The green and blue curves correspond to responses obtained from regions enriched in the 2222 and 1313 structural phases of La$_3$Ni$_2$O$_7$, respectively. The inset shows a polarized optical microscopy image of the same crystal; the green and blue markers indicate the locations where the corresponding Raman spectra were collected. (b) Powder x-ray diffraction pattern of a crushed single crystal together with a Rietveld refinement. The solid black line represents the calculated intensity from the refinement, the solid gray line shows the difference between the measured and calculated intensities, and the vertical blue/green bars mark the calculated Bragg peak positions. (c) Magnetic susceptibility of the La$_3$Ni$_2$O$_7$ single crystal shown in panel (a), measured in an applied field of 0.1 T along the $c$ axis (red) and within the $ab$ plane (black). Filled spheres denote zero-field-cooled (ZFC) data, while open triangles represent field-cooled (FC) measurements. (d) Temperature derivative of the susceptibility curve measured with the field applied along the $c$ axis [red symbols in panel (c)]. Arrows mark the anomalies associated with magnetic transitions.
• Figure 2: (a) Magnetic susceptibility of another La$_3$Ni$_2$O$_7$ single crystal measured in an applied field of 0.1 T along the $c$ axis (red) and within the $ab$ plane (black). Filled spheres denote zero-field-cooled (ZFC) data, while open triangles represent field-cooled (FC) measurements. The inset shows a polarized optical microscopy image of this crystal. (b) Temperature derivative of the susceptibility curve measured with the field applied along the $c$ axis [red symbols in panel (a)].
• Figure 3: Weak transverse field (WTF) $\mu$SR time spectra collected at $T = 5$ K and 300 K. Solid lines represent fits using Eq. \ref{['eq:WTF']}.
• Figure 4: Temperature dependence of the nonmagnetic volume fraction $1 - f_{\rm m}$ extracted from WTF $\mu$SR measurements. The solid line represents a fit using Eq. \ref{['eq:frac4']}, assuming three magnetic and one nonmagnetic component. The individual contributions to $1 - f_{\rm m}(T)$, as well as their total sum, are represented by the solid and dashed lines. See text for details.
• Figure 5: (a) Temperature dependence of the nonmagnetic volume fraction $1 - f_{\rm m}$ at $p = 0.0$ GPa. Open symbols correspond to data from the low-background GPS instrument, see Fig. \ref{['fig:WTF_nonmagnetic-fraction']}. (b) and (c) Temperature dependence of $1 - f_{\rm m}$ measured at $p = 1.2$ and 2.3 GPa. Solid lines are fits to Eq. \ref{['eq:frac4']} with parameters shown in each panel.