Antiferromagnetism with divalent Eu in ${\mathrm{EuNi}}_5{\mathrm{As}}_3$

We have successfully synthesized single crystals of ${\mathrm{EuNi}}_5{\mathrm{As}}_3$ using a flux method, and we present a comprehensive study of the physical properties using magnetic susceptibility, specific heat, electrical resistivity, thermoelectric power, and x-ray absorption spectroscopy (XAS) measurements. ${\mathrm{EuNi}}_5{\mathrm{As}}_3$ undergoes two close antiferromagnetic transitions at respective temperatures of $T_{N1}=7.2$ K and $T_{N2}=6.4$ K, which are associated with the ${\mathrm{Eu}}^{2+}$ moments. Both transitions are suppressed upon applying a field, and we map the temperature-field phase diagrams for fields applied parallel and perpendicular to the easy $a$ axis. XAS measurements reveal that the Eu is strongly divalent, with very little temperature dependence, indicating the localized ${\mathrm{Eu}}^{2+}$ nature of ${\mathrm{EuNi}}_5{\mathrm{As}}_3$, with a lack of evidence for heavy-fermion behavior.

Figure 1

(a) Crystal structure of ${\mathrm{EuNi}}_5{\mathrm{As}}_3$. (b) The powder x-ray diffraction pattern of polycrystalline ${\mathrm{EuNi}}_5{\mathrm{As}}_3$. The solid red line shows the calculated results of the Rietveld refinement, while the vertical bars show the theoretical Bragg peak positions and the green line shows the difference between the observed and calculated data.

Figure 2

(a) Magnetic susceptibility as a function of temperature of single crystals of ${\mathrm{EuNi}}_5{\mathrm{As}}_3$ with zero-field cooling. The inset shows $1/\chi$ against temperature and the corresponding Curie-Weiss fitting. (b) Low-temperature magnetic susceptibility for single crystals with zero field and field cooling, along with measurements of the polycrystalline sample.

Figure 3

(a) Temperature dependence of the specific heat $C\left(T\right)$ for single-crystalline ${\mathrm{EuNi}}_5{\mathrm{As}}_3$ and the isostructural compound ${\mathrm{SrNi}}_5{\mathrm{As}}_3$ in zero field. The inset shows the low-temperature region displaying two AFM transitions. (b) Magnetic specific heat $C_e\left(T\right)/T$ of ${\mathrm{EuNi}}_5{\mathrm{As}}_3$ after subtracting the lattice contribution. The magnetic entropy $\mathrm{\Delta }S\left(T\right)$ is also shown. The dashed line marks the position where the entropy is $Rln8$.

Figure 4

(a) Temperature dependence of the electrical resistivity $\rho \left(T\right)$ for single crystals of ${\mathrm{EuNi}}_5{\mathrm{As}}_3$. The inset shows $\rho \left(T\right)$ in the vicinity of the magnetic transitions. (b) Temperature dependence of the thermoelectric power for polycrystalline ${\mathrm{EuNi}}_5{\mathrm{As}}_3$ in zero applied field.

Figure 5

Temperature dependence of $\chi \left(T\right)$ under various applied magnetic fields with (a) $H\parallel a$ and (b) $H\perp a$.

Figure 6

(a) Field dependence of the magnetization $M\left(H\right)$ with $H\parallel a$ at 2 K. The inset shows the enlarged low field region measured upon both increasing and decreasing the field. The arrows indicate the metamagnetic transitions (b) $M\left(H\right)$ and the corresponding derivative $dM/dH$ with $H\perp a$ at 2 K. $M\left(H\right)$ at various temperatures is shown for (c) $H\parallel a$ and (d) $H\perp a$.

Figure 7

$C/T$ as a function of temperature down to 0.4 K under various magnetic fields, which are applied perpendicular to the $a$ axis.

Figure 8

Temperature dependence of electrical resistivity at various magnetic fields applied (a) parallel to the $a$ axis and (b) perpendicular to the $a$ axis. The curves are vertically shifted for clarity.

Figure 9

Magnetic field dependence of $\rho \left(H\right)$ at different temperatures for (a) $H\parallel \mathit{a}$ and (b) $H\perp \mathit{a}$.

Figure 10

Eu $L_{\text{III}}$ PFY-XAS spectra of ${\mathrm{EuNi}}_5{\mathrm{As}}_3$ at three different temperatures. The dotted line shows the Eu reference spectrum for ${\mathrm{EuCoO}}_3$(${\mathrm{Eu}}^{3+}$) for comparison.

Figure 11

The temperature-field phase diagram of ${\mathrm{EuNi}}_5{\mathrm{As}}_3$ for magnetic fields applied (a) parallel and (b) perpendicular to the $a$ axis. The transitions $T_{N1}$ and $T_{N2}$ are represented by red filled and blue open symbols respectively, while different symbols denote values obtained by different techniques. $T^{*}$ denotes the possible antiferromagnetic transition induced upon applying magnetic fields parallel to the $a$ axis.