Collinear spin density wave state in distorted square-lattice GdNiSn$_4$

Abstract

We characterize the magnetic ground state of the newly synthesized lanthanide intermetallic GdNiSn$_4$ via resonant elastic x-ray scattering measurements. This compound forms distorted square nets of Gd that initially order magnetically below 23 K followed by a lower temperature transition at 16 K. Our scattering data identify the ground state order as a single-$q$ incommensurate, collinear order that slides towards a commensurate wave vector above the 16 K transition. Magnetic symmetry analysis combined with azimuthal dependence resolves the ground state magnetic structure as a moment-modulated spin density wave state with Gd moments oriented parallel to the in-plane a-axis. We discuss connections between the observed magnetic order and electronic properties in this square-net compound.

Figures (4)

• Figure 1: Physical properties of distorted square-lattice GdNiSn$_4$. (a) Crystal lattice of GdNiSn$_4$ where differing structural motifs are labeled. The structure has been simplified for clarity; more detailed structural information is given in Ref. Zhang2025. Temperature dependent magnetic susceptibility with the applied field of $\mu_0 H = 0.1\;$T is shown applied (b) parallel to the $a$-axis, (c) and parallel to the $c$-axis. (d) Zero field $\rho_{yy}$. Note the transition at $\approx 4\;$K (denoted by $*$), is a a superconducting transition of residual Sn flux. (e) Specific heat capacity divided by temperature $C_p/T$ collected at zero field.
• Figure 2: Incommensurate magnetic order in GdNiSn$_4$. (a) Scattering geometry and linear polarization analysis schematic. (b) Energy dependence of the (0.56, 1, 10.22) peak, and fluorescence on the secondary axis. (c) $H$ dependence of magnetic peak with $\sigma \sigma'$ and $\sigma \pi'$ incoming and outgoing polarization. (d)-(f) High symmetry cuts of the magnetic peak along $H$, $K$ and $L$. All measurement were taken at 7.5 K.
• Figure 3: Temperature dependence of magnetic order of GdNiSn$_4$.$L$ scans taken at different temperatures across the (0.56, 1, 10.22) peak. The background has been subtracted and higher temperature scans have been offset for clarity. Solid lines are fits. Peak centers are marked. (b) Temperature dependence of the two fitted peak intensities. The solid green line as an order parameter fit to the $Q_1$ intensity, and the solid orange line is a Gaussian fit to the $Q_2$ intensity. (c) Temperature dependence of the two fitted peak centers. Hollow markers in (b) and (c) are the fitted values of the peak when intensity is too low compared to the other peak to be reliable.
• Figure 4: Determination of zero-field magnetic structure of GdNiSn$_4$. (a) Scattering geometry schematic for azimuthal dependent scans with varying incident polarization and without polarization analysis. (b), (c) Integrated intensities of rocking curves on $Q_1 = (0.56, 1, 10.22)$ at 7.5 K and $Q_2 = (0.56, 1, 10.24)$ at 20 K, with circularly polarized incident light. (d) ,(e) Integrated intensities of rocking curves on $Q_1$ at 7.5 K and $Q_2$ at 20 K with linearly polarized light. Solid lines are fits to the proposed magnetic structure, with a best fit value ofhe cant angle $\phi_1 = 99.9^\circ\pm1.5^\circ$ at 7.5 K, and $\phi_2 = 103.5^\circ\pm2.1^\circ$ at 20 K. $\phi$ is the angle of the moments from the $c$ axis. (f) Visualization of moment-modulated spin density wave structure, where $m \parallel a$. The $c$ axis has been shrunk for clarity.