Pressure studies on the antiferromagnetic Kondo semiconductor Ce(${\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x$)${}_2{\mathrm{Al}}_{10}$ ($x=0,0.1$)

We examined the electrical resistivity ($\rho$) of antiferromagnetic (AFM) Kondo semiconductors $\mathrm{Ce}({\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x$)${}_2{\mathrm{Al}}_{10}$ ($x=0$ and 0.1) under pressure in order to obtain information on the electronic states under pressure, especially near the critical pressure ($P_{\mathrm{c}}$) from the AFM ordered state to the paramagnetic one, where the $\mathrm{Ce}\text{−}4f$ electron character is a more localized state in $x=0.1$ than in $x=0$. From the results, nearly the same $P_{\mathrm{c}}$ was obtained; $P_{\mathrm{c}}\sim 4.7$ and 4.5 GPa in $x=0$ and 0.1, respectively. In both samples, the Kondo semiconducting increase of $\rho$ is observed up to $P\sim 3$ GPa, above which, however, the increase disappears and a broad maximum appears at high temperatures. Below the maximum, $\rho$ exhibits a metallic decrease with decreasing temperature down to the AFM transition temperature $T_0$, suggesting that the $c\text{−}f$ hybridization gap could be not necessary to form the unusual AFM order. We also examined pressure effects on the magnetic susceptibility $\chi$ of both samples up to $P\sim 2$ GPa, and found that $\chi$ along the easy axis is strongly suppressed by pressure in both samples. In $x=0$, the broad maximum just above $T_0$ shifts to high temperatures with increasing pressure. On the other hand, for $x=0.1$, a clear cusp at $T_0$ remains sharp and no broad peak appears at least up to 2 GPa. Such a difference in the pressure response of $\chi$ could originate from the difference in the electronic state between $x=0$ and 0.1.

Figure 1

Temperature dependence of the electrical resistivity ($\rho$) of $\mathrm{Ce}({\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x$)${}_2{\mathrm{Al}}_{10}$ ($x=0$ and 0.1) for $I\parallel a$ at ambient pressure, where the vertical scale is normalized by $\rho$ at $T=300$ K. The inset represents that plotted in a logarithmic temperature scale up to 300 K. The dotted line is a guide for eyes.

Figure 2

Temperature dependence of the electrical resistivity of ${\mathrm{CeRu}}_2{\mathrm{Al}}_{10}$ for $I\parallel a$ under pressures, where (a) $P<2$ GPa and (b) $P>2.5$ GPa. The insets of (a) and (b) are those at low temperatures.

Figure 3

Temperature dependence of the electrical resistivity of $\mathrm{Ce}({\mathrm{Ru}}_{0.9}{\mathrm{Rh}}_{0.1}$)${}_2{\mathrm{Al}}_{10}$ for $I\parallel a$ at various pressures, where (a) $P<3$ GPa and (b) $P>3$ GPa. The insets of (a) and (b) are those at low temperatures.

Figure 4

Temperature dependencies of the magnetic susceptibility of $\mathrm{Ce}({\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x$)${}_2{\mathrm{Al}}_{10}$ [(a) $x=0$ and (b) 0.1] under pressures, where $H\parallel a$.

Figure 5

(a) Pressure dependencies of the AFM transition temperature of $T_0$ in $\mathrm{Ce}({\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x$)${}_2{\mathrm{Al}}_{10}$ ($x=0$ and 0.1). That of $x=0$ reported in Ref. [6] is also shown for comparison. In (a), the temperature where the magnetic susceptibility along the $a$ axis shows a maximum ($T_{\chi }^{\max }$) of the sample with $x=0$ is also shown. (b) The maximum value of the magnetic susceptibility along the $a$ axis (${\chi }_a^{\max }$) plotted as a function of pressure for $x=0$ and 0.1.