Magnetic and electrical properties of the ternary compound ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ with one-dimensional uranium zigzag chains

The physical properties of the single-crystalline ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$, a new ternary uranium compound with ${\mathrm{U}}_2{\mathrm{Co}}_3{\mathrm{Si}}_5$-type orthorhombic structure, are investigated by means of magnetic susceptibility $\chi \left(T\right)$, specific heat $C\left(T\right)$, electrical resistivity $\rho \left(T\right)$, and high-field magnetization $M(H,T)$ measurements. ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ undergoes an antiferromagnetic transition at $T_N=36$ K followed by a first-order phase transition at $T_0=25.5$ K. The sharp peak in $C\left(T\right)$ at $T_0$ and the obvious hysteresis behavior in $\chi \left(T\right),\rho \left(T\right)$, and $M(H,T)$ around $T_0$ provide strong evidence for the first-order phase transition. The $\rho \left(T\right)$ measurements along the $a$ and $b$ axes reveal the negative temperature coefficients of resistance over a wide temperature range, which can be understood based on the semiconductorlike narrow band gap model or the Kondo effect. The $M\left(H\right)$ curve measured at 4.2 K along the $b$ axis shows three-step metamagnetic transitions within a narrow field region around 200 kOe and a large hysteresis near the first transition field, while the $M_{H\parallel a}\left(H\right)$ and $M_{H\parallel c}\left(H\right)$ curves show no transitions up to 560 kOe suggesting the strong magnetic anisotropy. A possible mechanism of the first-order phase transition at $T_0$ is the occurrence of a magnetic quadrupolar order, resulting from the quasi-one-dimensional uranium zigzag chain.

Figure 1

The crystal structure of ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$.

Figure 2

(a) Experimental and calculated results of powder x-ray diffraction of the pulverized ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ single crystal at room temperature. (b) The Laue pattern of ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ for the (001) plane.

Figure 3

Temperature dependences of ZFC susceptibility $\left(\chi =M/H\right)$ (a), and inverse susceptibility (b) of single crystalline ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ in a magnetic field of 500 Oe for $H\parallel a,H\parallel b$, and $H\parallel c$. The inset of panel (a) shows the expanded plot of ${\chi }_{H\parallel c}\left(T\right)$ curve. The solid lines in panel (b) display the fitting results of ${\chi }_{H\parallel b}\left(T\right)$ and ${\chi }_{H\parallel a}\left(T\right)$ using the modified Curie-Weiss law (see the text).

Figure 4

(a)–(c) Low temperature ZFC susceptibility of single crystalline ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ measured in magnetic fields of 55, 50, 40, 30, 20, 10, 2, and 0.5 kOe (curve from top to bottom) for $H\parallel a,H\parallel b$, and $H\parallel c$, respectively. (d)–(f) The expanded plot of the susceptibility around the transition temperature $T_0$ measured in magnetic fields of 55, 50, 40, 30, 20, 10, 2, and 0.5 kOe (curve from top to bottom) for $H\parallel a,H\parallel b$, and $H\parallel c$, respectively. The dotted lines in (b) and (e) are drawn to guide the eye.

Figure 5

Temperature dependence of specific heat $C\left(T\right)$ of single crystalline ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ plotted as $C/T$ vs $T$ down to 0.4 K. The inset shows the plot of $C/T$ vs $T^2$ at low temperatures.

Figure 6

(a) Temperature dependences of electrical resistivity of single crystalline ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ for measuring current parallel $a,b$, and $c$ axes $(I\parallel a,I\parallel b$, and $I\parallel c)$. The open triangle symbols represent the results of the least-square fits of the experimental data between 38 and 300 K to Eq. (1) for $I\parallel a$ (up triangle) and $I\parallel b$ (down triangle). Inset of (a): Expanded plot of the electrical resistivity in the high temperature region for $I\parallel c$. (b) Expanded plot of the electrical resistivity around the transition temperature $T_0=25.5$ K for $I\parallel a$ and $I\parallel b$. Inset of (b): Expanded plot of the electrical resistivity around transition temperature $T_0=25.5$ K for $I\parallel c$.

Figure 7

(a)–(c) Magnetization of single crystalline ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ measured between 0 and 55 kOe at temperatures of 40, 34, 32, 30, 27.5, 26, 25, 24, 22.5, 20, 15, 10, 5, and 2 K (curve from top to bottom) for $H\parallel a,H\parallel b$, and $H\parallel c$, respectively. The two dotted straight lines in (b) are drawn to guide the eye.

Figure 8

(a) High-field magnetization $M\left(H\right)$ of single crystalline ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$ measured at various temperatures for $H\parallel b$ and at 4.2 K for $H\parallel a$ and $H\parallel c$ (field sweep up). Inset of (a): Expanded plot of the $M_{H\parallel b}\left(H\right)$ curve near $H\sim 200$ kOe measured at $T=4.2\mathrm{K}$, which shows clear metamagnetic transition and hysteresis behavior. (b) The field derivative, $dM/dH$, in the field range 100–350 kOe for $H\parallel b$.

Figure 9

The magnetic phase diagram of ${\mathrm{U}}_2{\mathrm{Ir}}_3{\mathrm{Si}}_5$. The data were obtained by high-field magnetization (solid square: $H\parallel b)$ and dc-SQUID susceptibility (solid circle: $H\parallel b$; open triangle: $H\parallel a$ and $H\parallel c)$ measurements.