Growth, discovery and characterization of single crystalline Eu$_{0.8}$Pt$_6$Al$_{15.8}$

TL;DR

This work reports the discovery of a new Eu–Pt–Al ternary intermetallic, Eu$_{1-x}$Pt$_{6}$Al$_{16-y}$, grown as single crystals from a Eu-rich melt and linked to Eu$_{2}$Pt$_{6}$Al$_{15}$ growth attempts. Structural analysis shows a unique hexagonal lattice in space group $P\bar{6}2m$ with two Eu sites and partial Eu occupancy, yielding Eu$_{0.795(7)}$Pt$_{6}$Al$_{15.81(6)}$; EDS confirms the composition, while PXRD supports the refined model. Magnetic and electronic measurements reveal Eu$^{2+}$ moments ordering antiferromagnetically below $T_N = 2.8(2)$ K, with a Curie-Weiss moment of about $8.0$ and a Weiss temperature around $-5$ K, and metamagnetic features near 12 kOe along some directions, alongside defect-dominated metallic transport (RRR$<1.5$) and no resistive anomaly at $T_N$. The study demonstrates a new Eu-containing intermetallic with a distinct crystal structure and elucidates its low-temperature magnetism and structural chemistry, supported by comprehensive crystallography, magnetization, and transport data.

Abstract

We report the discovery of a ternary compound, Eu$_{0.8}$Pt$_6$Al$_{15.8}$. We determine its chemical and structural characteristics based on energy-dispersive X-ray spectroscopy as well as both powder and single-crystal X-ray diffraction, demonstrating that it crystallizes in a hexagonal structure type EuPt$_6$Al$_{16}$ with no reported structural analog. The electronic and magnetic properties are characterized by temperature- and field-dependent magnetization, and temperature-dependent resistance measurements, revealing that the Eu$^{2+}$ magnetic moments order antiferromagnetically below 2.8 K.

Figures (7)

• Figure 1: Crystal structure of Eu$_{0.8}$Pt$_6$Al$_{15.8}$, with the Eu atoms in blue, the Pt atoms in dark gray and the Al atoms in light gray: (a) including polyhedra around the Eu atoms in the $2c$ sites without vacancies (blue) and around the Eu atoms in the $2e$ sites with vacancies (cyan). (b) Photograph of one of the obtained single crystals. (c) Unit cell viewed down the $c$-axis; (d) unit cell viewed down the $a$-axis.
• Figure 2: Powder X-ray diffraction pattern measured for Eu$_{0.8}$Pt$_6$Al$_{15.8}$ (black symbols), the best fit obtained by Rietveld refinement (red line) and the residues (green line).
• Figure 3: Main panel: temperature-dependent magnetization of Eu$_{0.8}$Pt$_6$Al$_{15.8}$ normalized by the applied field of 50 Oe, oriented along $a$ (blue symbols), $b^*$ (red symbols) and $c$ (green symbols). All the shown results were done following both ZFC and FC protocls, which cannot be appreciated in the plot because they coincide with each other. A schematic diagram indicating the different directions with respect to the unit cell was also included. Inset: enlarged view of the low temperature range in order to visualize the feature in greater detail.
• Figure 4: Main panel: Magnetization of Eu$_{0.8}$Pt$_6$Al$_{15.8}$ as a function of the applied field, oriented along $a$ (blue), $b^*$ (red) and $c$ (green), measured at 2 K. The horizontal dashed line indicates the expected saturation magnetization for Eu$^{2+}$ ions. Inset: Enlarged view of the low-field results. The vertical dashed line indicates the field at which the $M(T)$ measurements were performed, and the overlapping black squares show the corresponding ZFC and FC magnetization at 2 K obtained from the $M(T)$ measurements done with a field of 50 Oe applied parallel to $c$.
• Figure 5: Low temperature polycrystalline average of the magnetic susceptibility of Eu$_{0.8}$Pt$_6$Al$_{15.8}$$\chi_{\text{ave}}$ (black, left axis), and $d(\chi_{\text{ave}}T)/dT$ (magenta, right axis) as a function of temperature.