Long-range magnetic phase transitions and negative magnetoresistance of divalent Eu in Eu₂Cu₅Ni₅ phase

We report the synthesis and physical properties of a new ternary Eu₂Cu₅Ni₅ phase which crystallizes in the orthorhombic space group Pmmm, No. 47, Z = 1, with lattice parameters; a = 4.015(4), b = 4.921(2) and c = 8.621(3) Å. Analysis from magnetic susceptibility χ_dc(T) results reveal an effective magnetic moment μ_eff = 7.8 μ_B/Eu that is comparable to the theoretical value of 7.93 μ_B for a divalent Eu²⁺ ion. The Eu²⁺ electronic state of 4f⁷ is well localized in this phase and the results preclude both the Cu and Ni sub-lattices from bearing a magnetic moment. Two long-range phase transitions pertaining to the Eu²⁺ moments are observed at T_C1 = 72 K and T_C2 = 47.2 K, followed by another anomaly at T_SR = 22 K, attributed to a spin re-orientation of Eu moments. The Seebeck coefficient S(T) attains a value of − 16.7 μV/K at room temperature (RT) and indicates that the electrons are the dominant charge carriers. Evidence from the electrical transport reveals a metallic behavior with the magnetotransport showing a negative magnetoresistance below RT.