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- a
nd 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$_{10}$.
A caged compound CeOs2Al10, crystallizing in the orthorhombic YbFe2Al10-type structure, undergoes a mysterious phase transition at T_0=29 K. We report the results of electron diffraction, magnetization, and magnetoresistance for single crystals. Supe
rlattice reflections characterized by a wave vector q = (0, -2/3, 2/3) observed at 15 K indicate a structural modification in the ordered state. Activation-type behavior of the electrical resistivity along the three principal axes below 50 K suggests gap opening in the conduction band. The magnetic susceptibility chi = M/B is highly anisotropic, chi_a>chi_c>chi_b, all of which sharply decrease on cooling below T_0. Furthermore, a metamagnetic anomaly in the magnetization and a step in the magnetoresistance occur at B=6-8 T only when the magnetic field is applied parallel to the orthorhombic c axis. However, T_0 hardly changes under magnetic fields up to 14 T, irrespective of the field direction. By using these data, we present a B-T phase diagram and discuss several scenarios for the mysterious transition.
We report on the electrical resistivity, magnetic susceptibility and heat-capacity measurements on a new intermetallic compound CePd5Al2, crystallizing in the ZrNi2Al5-type tetragonal structure, with lattice parameters a = 4.156 A and c = 14.883 A. T
he compound presents Kondo lattice behavior and an easy-plane antiferromagnetic ground state with two magnetic transitions at 2.9 K and 3.9 K. The Sommerfeld coefficient is estimated as 60 mJ/mol K^2.
