${\mathrm{YbV}}_3{\mathrm{Sb}}_4$ and ${\mathrm{EuV}}_3{\mathrm{Sb}}_4$ vanadium-based kagome metals with ${\mathrm{Yb}}^{2+}$ and ${\mathrm{Eu}}^{2+}$ zigzag chains

Here we present $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ and $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$, two compounds exhibiting slightly distorted vanadium-based kagome nets interleaved with zigzag chains of divalent ${\mathrm{Yb}}^{2+}$ and ${\mathrm{Eu}}^{2+}$ ions. Single crystal growth methods are reported alongside magnetic, electronic, and heat capacity measurements. $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ is a nonmagnetic metal with no collective phase transitions observed between 60 mK and 300 K. Conversely, $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$ is a magnetic kagome metal exhibiting easy-plane ferromagneticlike order below $T_{\text{C}}=32$ K with hints of modulated spin texture under low field. With $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ and $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$ we demonstrate another direction for the discovery and development of vanadium-based kagome metals while incorporating the chemical and magnetic degrees of freedom offered by a rare-earth sublattice.

Figure 1

$\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ and $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$ (a) are orthorhombic (Fmmm) compounds that exhibit a zigzag sublattice of Ln ions (b) interwoven with staggered layers of V-based kagome networks (c). Consistent with the orthorhombic structure, the kagome networks are slightly distorted (d). The distortion is relatively minor, and all V atoms are within 0.1 Å of the idealized kagome lattice. Some interatomic distances of interest are highlighted on the graphic.

Figure 2

(a) The electronic structure of Fmmm $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ calculated over an abbreviated portion of the face-centered (type-1) orthorhombic high-symmetry points shows Diraclike and flatbandlike features consistent with the vanadium kagome network. Most cleavage surfaces exhibit Yb–Sb termination, resulting in the scanning tunneling microscopy (STM) topograph and quasiparticle interference (QPI) patterns shown in (b), (c). Several energy- and momentum-dependent line cuts through the QPI patterns (red, green, blue) are shown (d) with bands highlighted via colored arrows. Though less common, crystals occasionally cleave along the V–Sb layers, resulting in the STM topograph shown in (e) and the corresponding QPI (f).

Figure 3

Bulk electronic properties characterization on single crystals of $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$. Temperature-dependent magnetization data are plotted in (a) with both orientations ($H\parallel c$ and $H|c$) revealing largely temperature-independent Pauli paramagnetism with a weak Curie tail from impurity spins. Isothermal magnetization [inset of (a)] shows no clear saturation and a magnitude (${10}^{-2}{\mu }_{\text{B}}$ per Yb) consistent with a small fraction of impurity spins. Zero-field resistivity measurements plotted in (b) confirm the metallic nature of $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ crystals. A simple quadratic fit to the low-temperature data is shown. Heat capacity results are plotted in (c). A nuclear Schottky anomaly is noted below 0.1 K. A Sommerfeld fit (red) is shown over a limited temperature range (blue) that avoids the Schottky anomaly.

Figure 4

Here we demonstrate a suite of magnetization data collected on single crystals of $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$. Temperature-dependent susceptibility collected on a crystal oriented with $H\parallel c$ (a) and $H\perp c$ (b) both exhibit a sharp upturn in magnetization, consistent with ferromagneticlike ordering near $T_{\text{C}}=32$ K. Note that an additional cusp and brief downturn in the susceptibility is noted when $H\parallel c$. Field-cooled measurements over a range of applied fields are plotted over the transition for $H\parallel c$ (c) and $H\perp c$ (d). Isothermal ZFC magnetization data are plotted in (e) highlighting rapid moment saturation and a weak coercivity (inset). Curie-Weiss analysis of the low-field susceptibility for both field orientations are plotted in (f).

Figure 5

Consistent with magnetization results, heat capacity measurements on single crystals of $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$ clearly show a lambdalike anomaly at $T_{\text{C}}=32$ K. The transition is field-dependent [(inset of (a)], broadening and weakly shifting toward lower temperatures. The transition is more obvious in $C_{\text{p}}/T$ (b), where direct subtraction of the scaled $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ nonmagnetic lattice reference yields the magnetic contribution to the total heat capacity. Integration of the magnetic heat capacity results in the magnetic entropy (c), yielding 97% of $Rln8$, consistent with divalent ${\mathrm{Eu}}^{2+}$.