Anisotropic magnetic properties of antiferromagnetic ${\mathrm{DyCoGa}}_5$

We report a detailed study of the physical properties of single crystals of ${\mathrm{DyCoGa}}_5$ using magnetic susceptibility, specific heat, and resistivity measurements. ${\mathrm{DyCoGa}}_5$ crystallizes in the layered tetragonal ${\mathrm{HoCoGa}}_5$-type structure and undergoes two successive antiferromagnetic transitions at $T_{N1}$ = 24.7 K and $T_{N2}=22.9$ K, which are associated with ordering of the ${\mathrm{Dy}}^{3+}$ moments. We characterize the temperature-field phase diagrams of ${\mathrm{DyCoGa}}_5$ for fields both along the $c$ axis and within the $ab$ plane, where highly anisotropic magnetic behaviors are observed. When fields are applied along the easy $c$ axis, both $T_{N1}$ and $T_{N2}$ are suppressed with increasing field, and multiple metamagnetic transitions are observed, while these transitions exhibit only a weak field dependence for $H\parallel ab$. From our analysis we propose a crystalline-electric-field scheme that gives rise to the observed Ising anisotropy, and a simple model of the magnetic exchange interactions can account for the low-temperature antiferromagnetic phase, as well as the field-induced phase with a magnetization half the saturated value.

Figure 1

Crystal structure of ${\mathrm{DyCoGa}}_5$, where orange, green, and blue represent the Dy, Ga, and Co atoms, respectively.

Figure 2

(a) The low-temperature magnetic susceptibility $\chi \left(T\right)$ of ${\mathrm{DyCoGa}}_5$ measured in an applied field of 0.1 T both parallel to the $c$ axis and in the $ab$ plane. (b) Temperature dependence of 1/$\chi$ up to 300 K for the two field directions, where the solid lines show the results from fitting with the CEF model described in the text.

Figure 3

(a) Temperature dependence of the magnetic specific heat $C_m$ of ${\mathrm{DyCoGa}}_5$ at low temperatures, obtained from subtracting an estimate of the lattice contribution from ${\mathrm{LuCoGa}}_5$. The red solid line shows the results from fitting with Eq. (5). The inset displays the total specific heat $C/T$ of ${\mathrm{DyCoGa}}_5$ (black) and the nonmagnetic analog ${\mathrm{LuCoGa}}_5$ (blue). (b) Temperature dependence of $C_m/T$ and the magnetic entropy $S_m$ of ${\mathrm{DyCoGa}}_5$, where the magenta solid line shows the specific heat calculated from the CEF model described in the text.

Figure 4

Temperature dependence of the resistivity $\rho \left(T\right)$ of ${\mathrm{DyCoGa}}_5$ and ${\mathrm{LuCoGa}}_5$, measured with the current in the $ab$ plane. (b) Temperature dependence of the magnetic contribution to the resistivity ${\rho }_{\mathrm{mag}}$ and the corresponding derivative $d{\rho }_{\mathrm{mag}}/dT$ of ${\mathrm{DyCoGa}}_5$, where ${\rho }_{\mathrm{mag}}$ was obtained from subtracting the ${\mathrm{LuCoGa}}_5$ data, after scaling the ${\mathrm{LuCoGa}}_5$ data so that the slope of the high temperature $\rho \left(T\right)$ was the same as that of ${\mathrm{DyCoGa}}_5$. The inset shows the low-temperature $\rho \left(T\right)$ of ${\mathrm{DyCoGa}}_5$, where the arrows correspond to the antiferromagnetic transitions $T_{N1}$ and $T_{N2}$. The red line shows the result from fitting the data in the AFM state using Eq. (6).

Figure 5

Temperature dependence of $C/T$ of ${\mathrm{DyCoGa}}_5$ measured in (a) zero field and various fields applied along the $c$ axis below 5 T and (b) fields applied along the $c$ axis beyond 5 T. The black, red, and olive arrows correspond to the transitions at $T_{N1}, T_{N2}$, and $T^{*}$, respectively.

Figure 6

(a)–(c) $\chi \left(T\right)$ of ${\mathrm{DyCoGa}}_5$ measured with various fields applied along the $c$ axis and in the $ab$ plane. (d)–(f) $\rho \left(T\right)$ of ${\mathrm{DyCoGa}}_5$ in various fields applied parallel to the $c$ axis and $ab$ plane, with the current in the $ab$ plane. The black, red, and green arrows correspond to the transitions at $T_{N1}, T_{N2}$, and $T^{*}$, respectively.

Figure 7

Field dependence of the magnetization $M\left(H\right)$ with $H\parallel c$ at (a) 2 K and (b) 7 K, where the arrows indicate the metamagnetic transitions $B_1, B_2$, and $B_3$. The isothermal $M\left(H\right)$ at various temperatures for fields applied parallel to the (c) $c$ axis and (d) $ab$ plane. Field dependence of the resistivity $\rho \left(H\right)$ with $H\parallel c$ at (e) 2 K and (f) 7 K, measured with the current in the $ab$ plane. The arrows correspond to the metamagnetic transitions observed in $M\left(H\right)$. The isothermal $\rho \left(H\right)$ are displayed at various temperatures for (g) $H\parallel c$ and (h) $H\parallel ab$.

Figure 8

Temperature-field phase diagrams of ${\mathrm{DyCoGa}}_5$ for magnetic fields applied (a) along the $c$ axis and (b) within the $ab$ plane based on specific heat, susceptibility, resistivity, magnetoresistivity, and magnetization measurements. (c) Field dependence of the magnetization $M\left(H\right)$ of ${\mathrm{DyCoGa}}_5$ at 5 K for $H\parallel c$. $J_1$ and $J_2$ represent magnetic exchange interactions between nearest-neighbor and next-nearest-neighbor Dy atoms within the $ab$ plane, and $J_3$ is between nearest-neighboring layers. The red dotted line shows $M\left(H\right)$ calculated from the mean-field model described in the text. The insets shows the proposed magnetic structures A, B, and C corresponding to phases II, III, and forced ferromagnetic states of ${\mathrm{DyCoGa}}_5$. (d) Scaling of the antiferromagnetic ordering temperatures of the $R{\mathrm{CoGa}}_5, R{\mathrm{CoIn}}_5$, and $R{\mathrm{RhIn}}_5$ series [22, 30, 31, 32, 33, 34] with the de Gennes factor ${(g_J-1)}^{2}J(J+1)$, where the dashed lines are guidelines for de Gennes scaling normalized by $T_M$ of the corresponding Gd analogs. The solid circles, open triangles, and open squares display the transition temperatures of $R{\mathrm{CoGa}}_5, R{\mathrm{CoIn}}_5$, and $R{\mathrm{RhIn}}_5$, respectively.