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

Abstract

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 are approximately determined as 30, 52, and 100 mJ/K 2 ·mol for NpFeGa 5 , NpRhGa 5 , and NpNiGa 5 , respectively. The magnetic susceptibility approximately follows the Curie–Weiss law at high temperatures (250 < T < 300 K) with effective magnetic moments ranging from 2.4 to 2.6 µ B /Np for NpRhGa 5 and NpNiGa 5 , indicating that the localized 5 f 4 electronic states are most likely applicable to these compounds at high temperatures.