Anisotropic Chemical Pressure Effect on the Antiferromagnetic Kondo Semiconductor Ce(Ru_1-xFe_x)₂Al₁₀

We have studied the Fe substitution effect on the anomalous antiferromagnetic (AFM) order in CeRu₂Al₁₀ by using both single- and poly-crystalline samples. Electron probe microanalysis revealed that the single crystals of Ce(Ru_1-xFe_x)₂Al₁₀ with 0.5 ≤ x ≤ 0.8, grown by an Al self flux method, separate into Ru-rich central part and Fe-rich surface part. On the other hand, the composition in the polycrystalline samples is homogeneous. The magnetic susceptibility, electrical resistivity and specific heat measurements on the polycrystals indicate that T_N gradually decreases and disappears at x = 0.7. This is contrasting to the pressure induced peaking of T_N at 2.5 GPa. We should remind that application of hydrostatic pressure and Fe substitution result in different lattice contractions. The rate of contraction by the hydrostatic pressure is almost isotropic up to P_c = 4 GPa, while that by Fe substitution is strongly anisotropic; Δa/a ≈ Δc/c ≈ 2Δb/b. Therefore, the contrasting changes of T_N by Fe substitution and by hydrostatic pressure suggest that the degree of c-f hybridization along the b-axis controls the anomalous AFM order in CeRu₂Al₁₀.