Magnetic behavior of Eu3Ni4Ga4: antiferromagnetic order and large magnetoresistance

The results of the magnetic susceptibility, isothermal magnetization, heat capacity, electrical resistivity and magnetoresistance measurements on polycrystalline Eu3Ni4Ga4 are presented. Eu3Ni4Ga4 forms in Na3Pt4Ge4-type cubic crystal structure (space group I 4-bar 3 m). The temperature dependence of the magnetic susceptibility of Eu3Ni4Ga4 confirms the divalent state (Eu2+) of Eu ions with an effective magnetic moment μeff = 7.98 μB. At low fields, e.g. at 0.01 T, a magnetic phase transition to an antiferromagnetically ordered state occurs at TN 10.9 K, which is further confirmed by the temperature dependence of the heat capacity and electrical resistivity. The field dependence of isothermal magnetization at 2 K reveals the presence of two field induced metamagnetic transitions at Hc1 and Hc2 = 0.55 and 1.2 T, respectively and a polarized phase above HPO = 1.7 T. The reduced jump in the heat capacity at the transition temperature, ΔC|TN = 13.48 J/mol-Eu K would indicate an amplitude modulated (AM) antiferromagnetic structure. An interesting feature is that a large negative magnetoresistance, MR = [ρ(H) - ρ(0)]/ρ(0), is observed in the vicinity of magnetic transition even up to 2TN. Similar large magnetoresistance has been observed in the paramagnetic state in some Gd and Eu based alloys and has been attributed to the magneto-polaronic effect. (paper)