Rapid growth of localized nature of carriers in the Kondo semiconductorCeFe2Al10with nonmagnetic ground state due to small Rh doping

Abstract

We examined the chemical doping effect on the Kondo semiconductor ${\mathrm{CeFe}}_{2}{\mathrm{Al}}_{10}$ with a nonmagnetic ground state by means of the magnetic susceptibility, specific heat, electrical resistivity, and thermopower. The effect of Ru doping on the ground state is small. On the other hand, by a small amount of Rh doping, the magnetic susceptibility is strongly enhanced along the orthorhombic $a$ axis, and a Curie-Weiss behavior is observed in a wide temperature range. The low-temperature specific heat is also strongly enhanced by the doping, and a metallic ground state is realized at low temperatures. These results suggest the collapse of the spin and charge gap due to the suppression of the $c\text{\ensuremath{-}}f$ hybridization effect. From the results of a crystalline electric field analysis on the magnetic susceptibility of $\mathrm{Ce}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}){}_{2}{\mathrm{Al}}_{10}$, it was revealed that the Rh-doping effect on the $c\text{\ensuremath{-}}f$ hybridization effect is anisotropic, especially for the $a$ axis. Similar doping effects are seen in the Rh-doped ${\mathrm{CeRu}}_{2}{\mathrm{Al}}_{10}$, Ir-doped ${\mathrm{CeOs}}_{2}{\mathrm{Al}}_{10}$, and Si-doped ${\mathrm{CeRu}}_{2}{\mathrm{Al}}_{10}$. From these results, we conclude that the collapse of the spin and charge gap by such an excess electron doping is one of the universal features of the Kondo semiconductor $\mathrm{Ce}{T}_{2}{\mathrm{Al}}_{10}$ ($T$ = Fe, Ru, and Os).