Magnetic behavior of Eu(3)Ni(4)Ga(4): antiferromagnetic order and large magnetoresistance.
The results of the magnetic susceptibility, isothermal magnetization,  heat capacity, electrical resistivity and magnetoresistance measurements on polycrystalline Eu(3)Ni(4)Ga(4) are presented. Eu(3)Ni(4)Ga(4) forms in Na(3)Pt(4)Ge(4)-type cubic crystal structure (space group [Formula: see text]). The temperature dependence of the magnetic susceptibility of Eu(3)Ni(4)Ga(4) confirms the divalent state (Eu(2+)) of Eu ions with an effective magnetic moment μ(eff) = 7.98 μ(B). At low fields, e.g. at 0.01 T, a magnetic phase transition to an antiferromagnetically ordered state occurs at T(N) = 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 H(c1) and H(c2) = 0.55 and 1.2 T, respectively and a polarized phase above H(PO) = 1.7 T. The reduced jump in the heat capacity at the transition temperature, ΔC|(T(N)) = 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 2T(N). 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.
Department of Physics, Indian Institute of Technology Kanpur, Kanpur-208016, India. anupam@iitk.ac.in
Anupam
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Geibel
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Hossain