Relation Between C-F Hybridization And Magnetic Ordering In Ceru2al10: An Optical Conductivity Study Of Ce(Ru1-Xrhx)(2)Al-10 (X <= 0.05)

A Kondo semiconductor CeRu2Al10 with an orthorhombic crystal structure shows unusual antiferromagnetic ordering at a rather high temperature T-0 of 27.3 K, which is lower than the Kondo temperature T-K similar to 60 K. In optical conductivity [rho(omega)] spectra that directly reflect the electronic structure, a c-f hybridization gap between the conduction and 4f states is observed at around 40 meV along the three principal axes. However, an additional peak at around 20 meV appears only along the b axis. By increasing x to 0.05 in Ce(Ru1-xRhx)(2)Al-10, the T-0 decreases slightly from 27.3 to 24 K, but the direction of the magnetic moment changes from the c axis to the a axis. Thereby, the c-f hybridization gap in the sigma(omega) spectra is strongly suppressed, but the intensity of the 20 meV peak remains as strong as for x = 0. These results suggest that the change in the magnetic moment direction originates from a decrease in the c-f hybridization intensity. The magnetic ordering temperature T-0 is not directly related to c-f hybridization but is related to the charge excitation at 20 meV observed along the b axis.