Magnetic and transport properties of EuNi(Si_1-xGe_x)₃ compounds

The magnetization M, electrical resistivity ρ, thermopower S and specific heat C of EuNi(Si_1-xGe_x)₃ compounds have been measured at temperatures from 2 to 300 K. For the compounds of EuNi(Si_1-xGe_x)₃, we obtained an effective magnetic moment of μ_eff ~ 7.7 μ_B, which is close to the divalent Eu value of μ_eff =7.94 μ_B. All compounds of EuNi(Si_1-xGe_x)₃ order antiferromagnetically. The Néel temperature T_N decreases monotonously with increasing the Ge concentration x from T_N=49 K for EuNiSi₃ to T_N=14 K for EuNiGe₃. In the low temperature region below T_N, anomalies corresponding to an additional magnetic phase transition into ferromagnetic state for compounds with x < 0.3, and into another antiferromagnetic for x > 0.3 were observed. The Curie temperature T_C rapidly decreases with increasing x and vanishes at x ≈ 0.3. It is found that the magnetic phase transition temperatures of T_N and T_C in EuNi(Si_1-xGe_x)₃ are strongly connected with the change of volume induced by the atomic substitution of Si by Ge.