Structural, magnetic, and electronic properties of a GdAsSe single crystal: Experimental and theoretical studies

We report high-quality single-crystal growth, x-ray diffraction, magnetic susceptibility [χ($T,H$)], magnetization [$M$($H$)], heat capacity $\left[C_{\mathrm{P}}(T,H)\right]$, electrical resistivity [ρ($T,H$)], and electron spin resonance (ESR) measurements of GdAsSe as functions of temperature and magnetic field. We identify an antiferromagnetic phase transition at $T_{\mathrm{N}}\sim 11.9\pm 0.2$ K and construct magnetic phase diagrams for $H||ab$ and $H||c$ axes based on the χ($T,H$) and $C_{\mathrm{P}}$($T,H$) data. Isothermal $M$($H$) curves along the $H||ab$ direction at 3 K exhibit a field-induced spin orientation at $H_{\mathrm{C}}\sim 3.78\mathrm{T}$. Both $M$($H$) and χ($T,H$) indicate an easy-plane-type anisotropy. The Curie-Weiss analysis of the high-temperature paramagnetic χ($T$) yields a negative Weiss temperature, suggesting dominant antiferromagnetic interactions between the Gd ions. Magnetic entropy reaches 83% of R ln8 at $T_{\mathrm{N}}$. The presence of residual entropy above $T_{\mathrm{N}}$ and the persistence of ESR critical broadening up to $\sim 3T_{\mathrm{N}}$ alludes to a degree of magnetic frustration in the studied material. The ρ($T$) data above $T_{\mathrm{N}}$ is well fitted to the Bloch-Grüneisen theory for metals. Further, density functional theory calculations reveal an antiferromagnetic ground state where the Gd atoms are coupled ferromagnetically in the $ab$ plane and antiferromagnetically along the $c$ axis.

Figure 1

(a) Crystal structure of GdAsSe. (b) Magnetic Gd atoms form a square-lattice layer in the $ab$ plane and As atoms constitute a zigzag chain along the $c$ axis. Different view perspectives of unequal triangular lattices (c)–(e) along the $a$ axis (c) and the $b$ axis (d).

Figure 2

(a) X-ray diffraction pattern of a single crystal of GdAsSe. (b) Rietveld refinement of x-ray diffraction data on a crushed single-crystals powder of GdAsSe.

Figure 3

STM images of GdAsSe. (a) Topographic image taken on the cleaved GdAsSe surface revealing the Se lattice (bias voltage, $V=-2$ V; current set point, $I=20\mathrm{pA}$ and $T=4.5$ K). The scale bar represents 3 nm. The dotted yellow circle, the yellow arrow, and the red arrow denote adatoms arising from the cleavage process, a Se vacancy, and a Gd impurity, respectively. (b) Corresponding Fourier-transformed image of (a). (c) Topographic image taken in the same field of view as in (a) with bias voltage, $V=1$ V. The red arrow denotes the same impurity in (a). (d) Corresponding Fourier-transformed image of (c). The red circles mark the Bragg peaks in (b) and (d). (e) and (f) Enlarged image centered at the Gd impurity marked by a red arrow in (a) and (b), respectively. The red crosses indicate the impurities location as a reference. The scale bar is 1 nm.

Figure 4

(a) Zero-field-cooled (ZFC) and field-cooled (FC) magnetic susceptibility of GdAsSe single crystal (left axis) and its reciprocal magnetic susceptibility for ZFC data (right axis) as a function of temperature at an applied magnetic field of 0.01 T for H||ab and $H\left|\right|c$. The green solid line is the Curie-Weiss law fit of the $T=20-300$ K data to χ($T$)∼$C$/($T-\theta$). (b) An enlarged view of the magnetic susceptibilities at the vicinity of $T_{\mathrm{N}}$ (left axis) and its derivatives for the ZFC data (right axis). The magnetic susceptibility versus temperature under various applied magnetic fields (c) for $H\left|\right|c$ and (d) H||ab.

Figure 5

Field dependence of the magnetizations measured at different selected temperatures along the H||ab plane and their derivatives (right axis). The inset shows the magnetization curve for $H\left|\right|c$ measured at $T=3$ K.

Figure 6

(a) Temperature dependence of $C_{\mathrm{P}}$($T,H$) along the $c$ axis for GdAsSe at ${\mu }_{0}H=0$ T. The inset depicts $C_{\mathrm{P}}$($T,H$) at various selected applied magnetic fields. The solid red line corresponds to the fitting as described in the text. (b) Magnetic specific heat $C_{\mathrm{mag}}$($T,H$) versus temperature in the left axis and the magnetic entropy $S_m$ versus temperature in the right axis.

Figure 7

The T-H magnetic phase diagrams drawn from the χ($T,H$) (open triangular symbols) and $C_{\mathrm{P}}$($T,H$) data (open circular symbols). The red solid curve is a fitting curve to the equation $H=H_0{\left[1-T_{\mathrm{N}}\left(H\right)/T_{\mathrm{N}}\left(H=0\right)\right]}^{0.5}$.

Figure 8

(a) Derivative of the ESR absorption spectra at selected temperatures for H||ab. The ESR spectra are fitted to a Dysonian profile (solid lines). (c) Semilogarithmic plot of the $g$ factor as a function of reduced temperature. (c) Log-log plot of the ESR linewidth Δ$H$ vs reduced temperature. The solid line represents a power-law fit.

Figure 9

Electrical resistivity ρ of GdAsSe as a function of temperature without an external magnetic field (a) and measured in selected magnetic fields (b). The inset of shows the field dependence of $T_{\mathrm{N}}$.

Figure 10

(a) Illustration of four possible magnetic states: A-AFM, AFM 1, AFM 2, and FM studied in this work. The purple arrows indicate the spin direction of Gd ions.

Figure 11

The exchange parameters $J_1, J_2, J_3, J_4$, and $J_5$ are the nearest neighbor, next-nearest neighbor, next-next-nearest neighbor, next-next-next-nearest neighbor, and next-next-next-next-nearest neighbor for Gd-Gd atoms, respectively. Magenta and green spheres indicate Gd and As ions, respectively. The Se ions between Gd layers are neglected for a clear view to $J_3$.

Figure 12

Atom-decomposed density of state (a) and orbital-decomposed Gd density of state of GdAsSe in the magnetic ground state A-AFM from $\mathrm{PBE}+U+\mathrm{SOC}$ (b).