Suppression of antiferromagnetic order and hybridization gap by electron- and hole-doping in the Kondo semiconductor CeOs$_{2}$Al$_{10}$

Abstract

The Kondo semiconductor CeOs$_{2}$Al$_{10}$ exhibits an antiferromagnetic (AFM) order at $T_\mathrm{N}= 28.5$ K, whose temperature is unexpectedly high for the small ordered moment of $0.3$ $\mu_\mathrm{B}/$Ce. We have studied the effects of electron- and hole-doping on the hybridization gap and AFM order by measuring the magnetization $M$, magnetic susceptibility $\chi$, electrical resistivity $\rho$, and specific heat $C$ on single crystals of Ce(Os$_{1-x}$Ir$_{x}$)$_{2}$Al$_{10}$($x \le 0.15$) and Ce(Os$_{1-y}$Re$_{y}$)$_{2}$Al$_{10}$($y \le 0.1$). The results of $M (B)$ indicates that the AFM ordered moment $\mu_\mathrm{AF}$ changes the direction from the $c$-axis for $x = 0$ to the $a$-axis for $x = 0.03$. With increasing $x$ up to 0.15, $T_\mathrm{N}$ gradually decreases although the $4f$ electron state becomes localized and the magnitude of $\mu_\mathrm{AF}$ is increased to $1$ $\mu_\mathrm{B}/$Ce. With increasing $y$, the $4f$ electron state is more delocalized and the AFM order disappears at a small doping level $y = 0.05$. In both electron- and hole-doped systems, the suppression of $T_\mathrm{N}$ is well correlated with the increase of the Sommerfeld coefficient $\gamma$ in $C(T)$. Furthermore, the simultaneous suppression of $T_\mathrm{N}$ and the semiconducting gap in $\rho (T)$ at $T > T_\mathrm{N}$ indicates that the presence of the hybridization gap is indispensable for the unusual AFM order in CeOs$_{2}$Al$_{10}$.