First order magnetic phase transition in tetragonal NpCu2Si2

Abstract Magnetization and Np 237 Mossbauer studies of the tetragonal compounds Np M 2 Si 2 ( M = Cr, Mn, Fe, Co, Ni, Cu) were performed. NpMn 2 Si 2 is ferromagnetic. All other compounds order antiferromagnetically. Only in NpCu 2 Si 2 the Mossbauer studies reveal a first order magnetic phase transition at T N = 34 K. It is interpreted in terms of Blume's model, originally developed for cubic UO 2 .