Anisotropy, frustration and saddle point in the twisted Kagome antiferromagnet ErPdPb

TL;DR

ErPdPb realizes a twisted kagome antiferromagnet in a noncentrosymmetric ZrNiAl-type lattice and orders antiferromagnetically below $T_{ ext{N}} = 2.2~ ext{K}$ with a pronounced easy-axis anisotropy. The study combines single-crystal growth, comprehensive magnetic/transport/thermodynamic measurements, and DFT+$U$ calculations with spin-orbit coupling, revealing a $ frac{1}{3}$ magnetization plateau along the $c$ axis, strong resistivity anisotropy, and a large magnetocrystalline anisotropy energy of about $8.3~ ext{meV}$ per formula unit. Band-structure analysis shows quasi-one-dimensional Fermi surfaces and a spin-split saddle point near the Fermi level, suggesting proximity to electronic instabilities. The results position ErPdPb as a platform to explore frustrated magnetism, low-dimensional spin dynamics, and potential quantum-critical phenomena under tuning, with implications for unconventional electronic states in twisted kagome lattices.

Abstract

The kagome lattice, with its inherent geometric frustration, provides a rich platform for exploring intriguing magnetic phenomena and topological electronic structures. In reduced-symmetry structures, such as twisted kagome systems involving rare earth elements, additional anisotropy can arise, enabling intriguing properties including spin-ice states, magnetocaloric effects, noncollinear magnetic ordering, and anomalous Hall effect. Here, we report the synthesis of single crystals of ErPdPb, which features a twisted kagome lattice net of Er atoms within the hexagonal ZrNiAl-type structure, and we investigate its magnetic, electronic, and thermal properties. The material exhibits antiferromagnetic ordering below 2.2 K, consistently observed in magnetic, transport, and heat capacity measurements. Magnetization measurements reveal 1/3 metamagnetic steps along the c-axis below the Néel temperature, suggesting an Ising-spin-like state on the twisted kagome lattice. A pronounced anisotropy between in-plane and out-of-plane resistivity is observed throughout the temperature range of 1.8-300 K, and the compound exhibits a significant frustration index of 13.6 (12.7) along the c-axis (ab-plane). Heat capacity measurements show a broad hump at 2.2 K, with an additional increase below 0.5 K. The anisotropic magnetic properties are further explored through density functional theory (DFT) calculations, which suggest strong easy-axis anisotropy, consistent with experimental magnetic measurements and crystal-field model expectations, and quasi-one-dimensional bands and a spin-split saddle point at the zone center.

Figures (8)

• Figure 1: Crystal structures of Kagome and Twisted Kagome system. (a) A planar prototypical kagome arrangement with corner sharing equilateral triangles forming a kagome structure in the ab-plane. In contrast, Figure (b) emphasizes a crucial structural variation, illustrating the twisted kagome net in the $ab$ plane (c) depicts the crystal structure of ErPdPb in 3D (d) $c$-axis view of the crystal structure emphasizing the twisted kagome net of Er atoms in the $ab$-plane.
• Figure 2: Optical image, single crystal precession image and FIB device of ErPdPb. (a) Optical image of a needle like crystal (b) Single crystal XRD precession image of (hk1) plane showing a hexagonal symmetry of ErPdPb (c) Laue pattern on single crystal of ErPdPb surface along a [210] direction (d) FIB fabricated Hall bar with [001] axis normal to the surface.
• Figure 3: Magnetic properties of ErPdPb. (a) Magnetic susceptibility measured in a magnetic field ($B=\mu_{0}H$) of 0.1 T applied along crystallographic $c$-axis ($\chi_c$) and within the $ab$-plane ($\chi_{ab}$) measured with a field-cooled (FC) protocol. Inset highlights a broad feature centered at 49 K for $\chi_{ab}$ (b). Inverse susceptibility of ErPdPb for $B$ along $c$-axis ($\chi^{-1}_{c}$) and along $ab$-plane ($\chi^{-1}_{ab}$). The dashed lines represent the Curie-Weiss (CW) fit to the data. (c) Magnetic moment for $B||c$-axis (red curve), and $ab$-plane (blue curve) measured at 1.8 K. (d) Magnetic moment for $B||c$-axis measured at 3, 15 and 50 K.
• Figure 4: Physical properties of ErPdPb. (a) Zero field Electrical resistivity as a function of temperature with $I$$||$$c$-axis ($\rho_{c}$) and I$||$ab-plane ($\rho_{ab}$). (b) Longitudinal Magnetoresistance for I$||$$ab$-plane with $B$$||$$c$-axis and (black curve) magnetization with field along same direction (red curve) overlayed on a single plot at 1.8 K. (c) Magnetoresistance measured with $B$$||$$ab$-plane and $I$$||$$c$-axis and magnetization with field along same direction overlayed on a same plot at 3 K. (d) Longitudinal magnetoresistance for I$||$$ab$-plane and B$||$$c$ at 40 K. (e) Longitudinal magnetoresistance for I$||$$c$-axis and $B$$||$$ab$ plane. (f) Heat Capacity as a function of temperature with inset showing low temperature range 0.5- 4 K. Inset clearly shows the broad anomaly at 2.2 K and sharp upturn below 0.5 K.
• Figure 5: Magnetocrystalline anisotropy energy (in meV/f.u.) in ErPdPb, represented by the variation of magnetic energy as a function of spin-axis rotation, calculated using DFT+$U$, with $U$=10 eV applied on Er-$4f$ orbitals.