Pressure studies on the antiferromagnetic Kondo semiconductor Ce( Ru1−xRhx ) 2Al10 ( x=0,0.1 )

We examined the electrical resistivity ($\ensuremath{\rho}$) of antiferromagnetic (AFM) Kondo semiconductors $\mathrm{Ce}({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}$)${}_{2}{\mathrm{Al}}_{10}$ ($x=0$ 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 $\mathrm{Ce}\text{\ensuremath{-}}4f$ 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; ${P}_{\mathrm{c}}\ensuremath{\sim}4.7$ and 4.5 GPa in $x=0$ and 0.1, respectively. In both samples, the Kondo semiconducting increase of $\ensuremath{\rho}$ is observed up to $P\ensuremath{\sim}3$ GPa, above which, however, the increase disappears and a broad maximum appears at high temperatures. Below the maximum, $\ensuremath{\rho}$ exhibits a metallic decrease with decreasing temperature down to the AFM transition temperature ${T}_{0}$, suggesting that the $c\text{\ensuremath{-}}f$ hybridization gap could be not necessary to form the unusual AFM order. We also examined pressure effects on the magnetic susceptibility $\ensuremath{\chi}$ of both samples up to $P\ensuremath{\sim}2$ GPa, and found that $\ensuremath{\chi}$ 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 $\ensuremath{\chi}$ could originate from the difference in the electronic state between $x=0$ and 0.1.