Antiferromagnetic order in NpRhGa5

NpRhGa5 develops antiferromagnetic order below TN = 37 K. Contrary to its NpCoGa5 counterpart, NpRhGa5 does not show any phase transition in applied magnetic fields up to 9 T, but undergoes a second magnetic transition-attributed to a reorientation of the magnetic moments from the c-axis to the basal plane-at T∗ = 32 K, as evidenced by magnetization, resistivity, specific heat and 237Np Mössbauer data. The latter also indicates the occurrence of a Np3+ charge state and an ordered Np moment of 0.96 μB. The comparison of the magnetic properties of NpRhGa5 and AnTGa5 (An = U, Np, Pu; T = Co, Rh) compounds confirms that AnRhGa5 and AnCoGa5 are driven by common underlying physics and shows that magnetic interactions are enhanced in AnCoGa5 compounds, suggesting a possible link with the enhanced superconductivity in PuCoGa5 compared to PuRhGa5.