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We herein describe our investigation of the superconducting and magnetic properties of the rare-earth ternary germanide intermetallic compounds La 2 Pt 3 Ge 5 and Pr 2 Pt 3 Ge 5 . Single crystals of La 2 Pt 3 Ge 5 and Pr 2 Pt 3 Ge 5 were synthesized using the high temperature metal flux method.Both types of crystal formed in a U 2 Co 3 Si 5 -type orthorhombic structure (space group Ibam). La 2 Pt 3 Ge 5 showed the onset of superconducting phase transition at T c = 8.1 K, which, to the best of our knowledge, is the highest T c of all the RE 2 T M 3 X 5 (RE = Rare Earth elements, T M = Transition metal, and X = s − p metal) superconductors, and from the specific heat data, it was found to have multi-gap superconductivity. Pr 2 Pt 3 Ge 5 showed both a superconducting phase transition at T c = 7.8 K and two antiferromagnetic transitions at T N 1 = 3.5 K and T N 2 = 4.2 K, which indicates the coexistence of superconductivity and magnetism. However, the correlation between the superconductivity and the magnetism was too weak to be observed. In its normal state, Pr 2 Pt 3 Ge 5 revealed strong magnetic anisotropy, probably due to the crystalline electric field effect.

We present the temperature dependent magnetization, M(T), and the resistivity, ρ(T), of EuCu2Ge2 and EuCu2Si2 in single crystalline form. The EuCu2Ge2, which is synthesized in single-crystalline form, shows two different magnetic transitions in M(T) at TMc=8.5 K and TMab=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 EuCu2Si2, M(T) shows a two step antiferromagnetic transition at TN1≈10 K and TN2≈4 K, which is smeared out under H⩾1 T, probably due to field induced spin orientation. The transition at TN2 is also manifested as a decrease in ρ(T) due to loss of magnetic scattering. Interestingly, another exotic transition is found at T=2 K in ρ(T) data. The ρ(T) values rapidly increase by two orders of magnitude from ρ=20 μΩ cm at T=2 K and reach ρ=5 mΩ cm at T=0.5 K, which is similar to a metal–insulator transition.

The temperature dependent magnetization M (T) and electrical resistivity (T) were measured to study the electron doping effect in Eu 1Ϫx La x B 6 (xϭ0, 0.005, 0.03, 0.05, and 0.1͒. At room temperature, (T) decreases systematically with an increasing amount of electron doping. For a small doping with xϭ0, 0.005, and 0.03, M (T) exhibits ferromagnetic transitions and (T) reduces drastically below the transition, which also reveals characteristics of double transition. It is clearly found from both M (T) and (T) that the doped carriers in the region of xϽ0.03 lower the transition temperature. For the doping level with xϭ0.05, and 0.01, the groundstate properties look quite different from the ones of EuB 6 . While M (T) shows a ferromagneticlike behavior at low temperature, an increase of (T) around the ferromagneticlike region, rather than a reduction, is observed. This (T) behavior looks similar to the one in SmB 6 , which shows the opening of a Kondo insulating gap.

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