Magnetic and Electrical Properties of NpTGa5 (T=Fe, Rh and Ni)

We grew high-quality single crystals of NpTGa 5 (T = Fe, Rh, and Ni) with a tetragonal structure by the Ga-flux method and measured their electrical resistivity, specific heat, magnetic susceptibility, and magnetization. All the investigated compounds undergo magnetic ordering. NpFeGa 5 orders antiferromagnetically at T N =118 K and shows another magnetic transition at T * =78 K. A relatively large electrical resistivity indicates that NpFeGa 5 might be a low-carrier compound. NpRhGa 5 also orders antiferromagnetically at T N1 =36 K. Below another magnetic transition at T N2 =32 K, the antiferromagnetic easy-axis is most likely changed from [001] to the (001) plane. On the other hand, NpNiGa 5 undergoes ferromagnetic ordering at T C =30 K, where the magnetic moment of Np is directed along the [001] direction. Furthermore, below another magnetic transition at T * =18 K, the ordered moment is discontinuously enlarged and a change of the magnetic structure occurs. The electronic specific heat coefficients ar...