Magnetic properties and heavy electronic states in the antiferromagnet NpPtGa₅

We succeeded in growing a new neptunium compound NpPtGa₅ by the Ga-flux method, and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas-van Alphen (dHvA) effect. NpPtGa ₅ orders antiferromagnetically below T_N = 26 K. The magnetic moment is most likely directed along the [100] direction. A cylindrical Fermi surface was detected by the dHvA experiment in the antiferromagnetic state. The cyclotron masses are large, 17-21 m₀, indicating the heavy electronic state in NpPtGa₅. The large cyclotron masses are consistent with the large electronic specific heat coefficient, γ = 123 mJ/(K²·mol), which is the largest among NpTGa₅ (T = Fe, Co, Rh, Ni, and Pt).