Anisotropic antiferromagnetic order in EuPd$_3$Si$_2$

TL;DR

This work investigates the magnetic ground state of EuPd$_3$Si$_2$, a Eu-based intermetallic with localized 4$f$ moments, addressing discrepancies with earlier reports of ferromagnetism. Through EuPd-flux crystal growth, comprehensive structural analyses, and magnetization, transport, and heat-capacity measurements along the principal crystallographic axes, the study finds antiferromagnetic order below $T_{ m N1}=61\, \mathrm{K}$ and a spin reorientation at $T_{ m N2}=40\, \mathrm{K}$, with moments likely aligned along [100] between the two transitions and strong anisotropy in the phase diagrams. A key insight is that a modest Pd substitution on Si sites (~7%) and slight lattice parameter shifts yield notable changes in Eu–Eu distances, which can tune the RKKY exchange and switch the ground state away from the ferromagnetic order reported in prior work, underscoring the sensitivity of Eu-based magnetism to structural and compositional details. Overall, the results demonstrate that small growth-condition–induced changes in structure and composition can drastically alter magnetic interactions in Eu compounds, suggesting potential routes to strain-engineer magnetic order in these systems.

Abstract

Single crystals of EuPd$_3$Si$_2$ were grown using a high-temperature EuPd-flux method. The material was structurally and chemically characterized by single-crystal x-ray diffraction, powder x-ray diffraction, Laue method and energy-dispersive x-ray spectroscopy. The structural analysis confirmed the orthorhombic crystal structure (space group $Imma$) but revealed differences in the lattice parameters and bond distances in comparison to previous work by Sharma et al.. The composition is close to the ideal 1:3:2 stoichiometry with an occupation of 7 % of the Si sites by Pd. The heat capacity, electrical resistivity, and magnetic susceptibility show two magnetic transitions indicating antiferromagnetic ordering below $T_{\rm N1}= 61\,\rm K$ and a spin reorientation at $T_{\rm N2}= 40\,\rm K$. The orthorhombic material shows magnetic anisotropy with field applied along the three main symmetry axes, which is summarized in the temperature-field phase diagrams. The susceptibility data hint to an alignment of the magnetic moments along $[100]$ between $T_{\rm N1}$ and $T_{\rm N2}$. Below $T_{\rm N2}$ the magnetic structure changes to an arrangement with moments canted away from $[100]$. In contrast to published work by Sharma et al., the single crystals investigated in this study show AFM order below $T_{\rm N1}$ instead of ferromagnetism that sets in at higher $T_{\rm C1}=78\,\rm K$ which might originate from certain differences in the structure, composition or defects that have an impact on the dominant coupling constants of the RKKY interaction.

Figures (12)

• Figure 1: (a) Schematic drawing of the set up consisting of a graphite crucible with the elements in a sealed niobium crucible, that was welded under vacuum in a quartz ampoule. (b) A sample cut along the main symmetry directions with the corresponding Laue image. (c) Unit cell of EuPd$_3$Si$_2$ with Pd excess. The distance between the Eu-atoms along the $a$ axis is d$_{\rm 1}$ = 3.6258(1) Å. (d) Unit cell projected onto the $b-c$ plane. The distances between the six surrounding Eu-atoms d$_{\rm 2}$ = 5.7393(5) Å, d$_{\rm 3}$ = 6.0062(3) Å, and d$_{\rm 4}$ = 5.5800(3) Å are depicted.
• Figure 2: Heat capacity as function of temperature for different magnetic fields. The inset shows the measurement of the heat capacity as function of temperature up to 200 K. (b) The peak at $T_{\rm N1}$ shifts to lower temperatures with higher magnetic fields. (c) At high temperatures, the heat capacity approaches the Dulong-Petit limit of 150 J/(mol K).
• Figure 3: (a) Normalized electrical resistivity as function of temperature for the current applied along the $[100]$ and $[010]$ directions. Inset (b) shows the resistivity measured for different magnetic fields applied along the $[100]$ direction, while inset (c) presents the resistivity for fields applied along $[001]$.
• Figure 4: Magnetic moment per Eu as function of the magnetic field for field applied along the three main symmetry directions at 2 K. The inset shows exemplary the evaluation of the critical field $B_c^{001}$ (arrow) which is determined by the intersection points of two linear regressions. The data in gray are taken from sharma2023crystal.
• Figure 5: Comparison of the behavior of $M/H$ versus $\mu_0H$ at low fields along the three main directions at (a) $T = 5~\rm K$ and at (b) 50 K.