Magnetic anisotropy and electronic transport properties in the single-crystalline compounds of EuCu_2Ge2 and EuCu_2Si_2

We present the temperature dependent magnetization, M(T), and the resistivity, ρ(T), of EuCu_2Ge₂ and EuCu_2Si₂ in a single crystalline form. The EuCu_2Ge_2, which is synthesized in a single crystalline form for the first time in our knowledge, shows two different magnetic transition in M(T) at T_M_c= 8.5 K and T_M_ab= 4 K depending upon the magnetic field orientation. On the other hand, the ρ(T) reveals only one transition at T= 4 K as a sudden drop of the ρ(T) without any noticeable change at T= 8.5 K. For the EuCu_2Si_2, M(T) shows two step AF transition at T_N1 10 K and T_N2 4 K, which is smeared out under H>= 1 T, probably due to field induced spin orientation. The transition at T_N2 is also manifested as a decrease in ρ(T) due to magnetic scattering loss. Interestingly, another exotic transition is found at T= 2 K in ρ(T) data for the first time. ρ(T) values rapidly increase by two orders of magnitude from ρ= 20 μΩ-cm at T= 2 K, reaching to ρ= 5 mΩ-cm at T= 0.5 K, which is similar to the metal-insulator transition.