Antiferromagnetic order competing with topological state in Ce_xBi_2−xTe₃

The topological surface states in three-dimensional topological insulators are easily tuned by chemical doping, especially by magnetic impurities. We prepared single crystals of Ce_xBi_2−xTe₃ with various x (=0.04, 0.06, 0.08, 0.10, and 0.12). The obtained crystals were characterized by X-ray diffraction and scanning electron microscopy. The magnetic susceptibility data revealed that the Ce atoms are well substituted for Bi into Bi₂Te₃. From the Curie-Weiss fits, we observed that the effective magnetic moments μ_eff are close to 2.54 μ_B for free Ce ion, and the paramagnetic Curie-Weiss temperatures θ_p are negatively increased from 2.87 K to −59.3 K with increasing x. The magnetization data clearly showed antiferromagnetic orders around T_N = 4.1 K for x ≥ 0.08, where θ_p suddenly increases, and the electrical resistivity is simply metallic and the magnetoresistance is parabolic. Only for x = 0.06, exotic physical properties arising from the topological states were observed such as non-metallic behavior in the electrical resistivity and linear dependence of the magnetoresistance. Moreover, the carrier concentration of x = 0.06 is one order lower than that of x ≥ 0.08. These observations propose that the antiferromagnetic order is strongly competing with the topological state in Ce_xBi_2−xTe₃.